JP2024102584A - Adhesive sheet - Google Patents

Abstract

To provide an adhesive sheet that can be suitably adhered to an adherend and has good removability from the adherend.SOLUTION: An adhesive sheet includes: a base material; a first adhesive layer disposed on one side of the base material; and a second adhesive layer disposed on a side opposite to the first adhesive layer of the base material. At least a surface of the second adhesive layer is composed of an adhesive containing heat-expandable microspheres. A thickness of the first adhesive layer is 20-70 μm.SELECTED DRAWING: Figure 1

Description

The present invention relates to an adhesive sheet.

In general, adhesives (also called pressure-sensitive adhesives; the same applies below) have the property of being in a soft solid (viscoelastic) state at temperatures near room temperature and adhering to an adherend under pressure. Taking advantage of such properties, adhesives are widely used in various industrial fields, typically in the form of an adhesive sheet having an adhesive layer. One example of the use of an adhesive sheet is as a so-called processing material, which is temporarily attached to an adherend during the manufacture, processing, transportation, etc. of various articles that are adherends, and is removed from the adherend after the purpose is achieved. For example, in the manufacture of semiconductor parts including semiconductor chips, in a resin sealing process in which the semiconductor chips are resin-sealed to prevent the semiconductor chips from being scratched and to expand the metal wiring, etc., the resin sealing of the semiconductor chips may be performed on an adhesive sheet from the viewpoint of workability, etc. For example, multiple semiconductor chips are placed on the adhesive layer of an adhesive sheet as a temporary fixing material, and the semiconductor chips are collectively sealed on the adhesive layer. Thereafter, in a specified post-process, the adhesive sheet is peeled off from the structure including the sealing resin and the semiconductor chips.

JP 2001-308116 A JP 2001-313350 A

For example, adhesive sheets used as processing materials are required to adhere well to the adherend during a specified process and to be easily removable from the adherend when removed from the adherend. With regard to adhesion to the adherend, for example, adhesive sheets used in the resin sealing process of the semiconductor chips described above are required to fix the adherend, that is, the semiconductor chip, without misalignment. With regard to removability from the adherend, it is desirable for the adhesive sheet to have light releasability suitable for preventing damage to the adherend due to the load when peeling the adhesive sheet, and to have the property of not leaving any adhesive residue (glue residue) on the adherend after peeling the adhesive sheet. For example, an adhesive sheet that is expected to be used in a manner in which the adherend is subjected to processing involving heating while attached to the adherend, such as the resin sealing process of the semiconductor chips described above, is required to exhibit the light releasability and anti-glue residue properties even after heating.

One method for making the adhesive sheet easy to peel off is to make the adhesive moderately hard. Hardening the adhesive is also advantageous from the viewpoint of preventing adhesive residue due to cohesive failure of the adhesive. However, when the adhesive is hardened, the adhesive tends to have a lower adhesion to the adherend, and it tends to be difficult to fix the adherend without shifting. For example, in the above-mentioned semiconductor chip resin encapsulation process application, if the adhesive does not have sufficient adhesion to the adherend, the semiconductor chip may shift in position by about several tens of microns during the resin encapsulation process, which may cause a decrease in yield and defects. In addition, in an adhesive sheet having an adhesive layer on a substrate, when the adhesive is hardened, the adhesion between the substrate and the adhesive layer decreases, and adhesive residue is more likely to occur due to anchor failure (peeling at the interface between the substrate and the adhesive layer).

Although the adhesion to the adherend can generally be improved by increasing the thickness of the adhesive layer, depending on the use form and application location of the adhesive sheet, it is expected that there will be disadvantages to increasing the thickness of the adhesive layer. For example, in an adhesive sheet that is peeled off from an adherend after achieving the purpose of fixing the adherend, if the adhesive layer is thick, adhesive residue is likely to occur due to cohesive failure when the adhesive sheet is peeled off. In addition, in the above-mentioned semiconductor chip resin sealing process application, if the adhesive layer is thick, the semiconductor chip fixed on the adhesive layer is likely to sink into the surface of the adhesive layer due to pressure during resin sealing, and there is a concern that a step (standoff) is likely to occur between the semiconductor chip and the sealing resin after the adhesive sheet is peeled off. The above-mentioned step may reduce the wiring formability from the semiconductor chip to the surrounding sealing resin and the protection of the semiconductor chip, so it is desirable to reduce it. For such reasons, the thickness of the adhesive layer used in the above-mentioned semiconductor chip resin sealing process has traditionally been limited to about 10 μm.

The inventors of the present invention have conducted intensive research into the above-mentioned problems, and have found that in adhesive sheets used in the resin encapsulation process of semiconductor chips, the components in the epoxy resin used as the encapsulating resin migrate to the adhesive layer, increasing the adhesion between the encapsulating resin and the adhesive, making it easier for heavy peeling and adhesive residue to occur. Based on this knowledge, it is believed that light peeling and adhesive residue prevention can be improved by reducing the amount of components that migrate from the encapsulating resin on the surface of the adhesive layer. In addition, the inventors have found that the level of the step between the semiconductor chip and the encapsulating resin can depend on the concentration of the components that migrate from the encapsulating resin to the adhesive layer in the resin encapsulation process. Specifically, the thicker the adhesive layer is, the lower the concentration of the components that migrate from the encapsulating resin is as a whole, resulting in improved adhesive residue prevention and reduced step between the semiconductor chip and the encapsulating resin, a result that differs from conventional technical common sense. The present invention has been created based on the above-mentioned findings, and aims to provide an adhesive sheet that can adhere well to an adherend even when used in the resin encapsulation process of semiconductor chips, and that is easily removable from the adherend.

The pressure-sensitive adhesive sheet provided by this specification comprises a substrate, a first pressure-sensitive adhesive layer disposed on one side of the substrate, and a second pressure-sensitive adhesive layer disposed on the opposite side of the substrate to the first pressure-sensitive adhesive layer. At least the surface of the second pressure-sensitive adhesive layer is made of a pressure-sensitive adhesive containing heat-expandable microspheres. The thickness of the first pressure-sensitive adhesive layer is 20 μm or more and 70 μm or less.
According to the configuration including the first adhesive layer having a thickness of 20 μm or more, for example, in an embodiment in which an adhesive sheet is used in a resin sealing process of a semiconductor chip, the components that migrate from the sealing resin to the first adhesive layer diffuse into the first adhesive layer and become low in concentration overall, the concentration of the migration components on the surface of the first adhesive layer decreases, and adhesive residue caused by the migration components from the adherend side is unlikely to occur on the surface of the first adhesive layer. In addition, since the thickness of the first adhesive layer is 70 μm or less, adhesive residue due to cohesive failure of the first adhesive layer is unlikely to occur. Furthermore, the first adhesive layer can be well adhered to the adherend. In short, according to the above configuration, an adhesive sheet that can be well adhered to the adherend and has good removability from the adherend is realized. In addition, when the adhesive sheet of the above configuration is used in a resin sealing process of a semiconductor chip, the step between the semiconductor chip and the sealing resin can be reduced by having the thickness of the first adhesive layer be 20 μm or more.
In addition, the pressure-sensitive adhesive sheet having the above-mentioned configuration has a second pressure-sensitive adhesive layer, and at least the surface of the second pressure-sensitive adhesive layer is composed of a pressure-sensitive adhesive containing heat-expandable microspheres, so that, for example, the second pressure-sensitive adhesive layer can be used to fix the sheet on a suitable object to be fixed (second adherend), and in that state, processing of the first adherend that is in close contact with the surface of the first pressure-sensitive adhesive layer (for example, a resin sealing step on the first pressure-sensitive adhesive layer) can be performed, making the sheet easy to use. In addition, the pressure-sensitive adhesive sheet can be heated at an appropriate timing as necessary to expand the heat-expandable microspheres, so that the bonding between the second pressure-sensitive adhesive layer and the second adherend can be easily released.

In some embodiments, the first pressure-sensitive adhesive layer has an increase in peak intensity derived from the epoxy resin before and after the epoxy resin treatment of the surface of the first pressure-sensitive adhesive layer, which is determined based on the peak intensity present in the range of 1725 cm ^-1 to 1750 cm ^-1 in the FT-IR spectrum at a measurement position located at a depth of 5 μm from the substrate side of the first pressure-sensitive adhesive layer, within a range of 0.000 to 0.030. Here, as the peak intensity derived from the epoxy resin, a peak intensity present in the range of 1505 cm ^-1 to 1515 cm ^-1 is used. By limiting the increase in peak intensity derived from the epoxy resin to 0.030 or less, for example, in an embodiment in which the pressure-sensitive adhesive sheet is used in a resin sealing process of a semiconductor chip, the migration component from the epoxy sealing resin is suppressed to a predetermined amount or less in the first pressure-sensitive adhesive layer, and adhesive residue caused by the migration component from the adherend side is less likely to occur on the surface of the first pressure-sensitive adhesive layer.

In some embodiments, the first adhesive layer has an adhesion to epoxy resin (adhesion to epoxy resin) of 0.01 N/10 mm or more and 3.00 N/10 mm or less, measured at 100° C. after treating the surface of the first adhesive layer with an epoxy resin, and an adhesion to polyethylene terephthalate film (adhesion to PET) of 1.00 N/20 mm or more and 10.0 N/20 mm or less, measured in an environment of 23° C. and 50% RH. According to an adhesive sheet in which the adhesion to epoxy resin of the first adhesive layer is within the above range, for example, in an embodiment in which the adhesive sheet is used in a resin sealing process for semiconductor chips, the first adhesive layer adheres well to the sealing resin, while being less likely to leave adhesive residue when peeled off from the sealing resin. In addition, with an adhesive sheet in which the adhesive strength to PET of the first adhesive layer is within the above range, the first adhesive layer can preferably fix an adherend (e.g., a semiconductor chip), and adhesive residue is less likely to be left on the adherend when the first adhesive layer side of the adhesive sheet is peeled off from the adherend. In applications in resin sealing processes for semiconductor chips, the chip retention is good and chip shift can be preferably prevented.

In some embodiments, the first adhesive layer has a storage modulus at 23°C of 0.10 MPa or more and 0.50 MPa or less. An adhesive having a storage modulus at 23°C within the above range has appropriate flexibility and elasticity, and is likely to achieve both adhesion to the adherend and prevention of adhesive residue.

In some embodiments, the first pressure-sensitive adhesive layer has a ratio of a peak intensity present in the range of 1700 cm ^-1 to 1710 cm ^-1 to a peak intensity present in the range of 1725 cm ^-1 to 1750 cm ^-1 in an FT-IR spectrum of 0.325 or less. By having the peak intensity ratio of 0.325 or less, for example, in an embodiment in which the pressure-sensitive adhesive sheet is used in a resin sealing process of a semiconductor chip, the components that have migrated from the sealing resin to the first pressure-sensitive adhesive layer are easily dispersed throughout the first pressure-sensitive adhesive layer and are not easily unevenly distributed on the surface of the first pressure-sensitive adhesive layer. This tends to make it more difficult for adhesive residue to occur on the surface of the first pressure-sensitive adhesive layer due to the components that migrate from the adherend side.

In some embodiments, the first adhesive layer includes an acrylic polymer. The monomer components constituting the acrylic polymer contain 10 to 70% by weight of (meth)acrylic acid alkyl ester having a linear or branched alkyl group with 6 or less carbon atoms. By using an acrylic polymer having the above monomer composition, the glass transition temperature of the acrylic polymer can be set to an appropriate range that can preferably achieve both adherend adhesion and adhesive residue prevention. In addition, since the number of relatively short side chains of the acrylic polymer is within a predetermined range, the polarity is appropriately controlled. For example, in an embodiment in which the adhesive sheet is used in the resin sealing process of semiconductor chips, component migration from the sealing resin to the first adhesive layer is suppressed, and adhesive residue caused by components migrating from the adherend side tends to be less likely to occur on the surface of the first adhesive layer.

When the adhesive sheet disclosed herein is used in a resin encapsulation process for semiconductor chips, it can adhere well to the semiconductor chip as an adherend, and therefore has good chip retention and good removability of the encapsulation resin. Therefore, it is particularly suitable for the resin encapsulation process for semiconductor chips. The use of the adhesive sheet disclosed herein is not limited to the use in the resin encapsulation process for semiconductor chips, and it can be applied to various uses. For example, the adhesive sheet disclosed herein is relatively low elastic and thicker than conventional adhesive sheets, and can exhibit good removability from the adherend, such as preventing adhesive residue, so that it is also suitable as a processing adhesive sheet used for processing various devices such as small devices and devices with surface irregularities, taking advantage of its flexibility and adherend adhesion.

1 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to an embodiment. 2(i) to 2(iv) are explanatory views showing an example of a semiconductor chip resin sealing process carried out using the adhesive sheet shown in FIG. 1. 3(i) to 3(iv) are explanatory views showing an example of the case where a conventional adhesive sheet is used in the semiconductor chip resin sealing step shown in FIG. 2.

Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field.
In the following drawings, the same reference numerals may be used to denote components or parts having the same function, and duplicated descriptions may be omitted or simplified. In addition, the embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the product actually provided.

In this specification, the "base polymer" of a pressure-sensitive adhesive refers to the main component of the rubber-like polymer contained in the pressure-sensitive adhesive, and is not to be construed in any other limiting sense. The rubber-like polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In addition, in this specification, the "main component" refers to a component that is contained in an amount of more than 50% by weight, unless otherwise specified.
In addition, in this specification, the term "acrylic polymer" refers to a polymer containing a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule as a monomer unit constituting the polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer". Therefore, the acrylic polymer in this specification is defined as a polymer containing a monomer unit derived from an acrylic monomer. A typical example of an acrylic polymer is a polymer in which the proportion of the acrylic monomer in the total monomers used in the synthesis of the acrylic polymer is more than 50% by weight (preferably more than 70% by weight, for example more than 90% by weight). Hereinafter, the monomer used in the synthesis of the polymer is also referred to as a monomer component constituting the polymer.
In this specification, "(meth)acryloyl" refers collectively to acryloyl and methacryloyl. Similarly, "(meth)acrylate" refers collectively to acrylate and methacrylate, and "(meth)acrylic" refers collectively to acrylic and methacrylic. Therefore, the concept of an acrylic monomer here can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer).

<Summary of adhesive sheet>
The adhesive sheet disclosed herein can be suitably used as a processing material that is temporarily attached to an adherend during the manufacture, processing, transport, etc. of various articles that are adherends, and is removed from the adherend after the purpose is achieved. One example of such an application is as a temporary fixing material when resin-encapsulating a semiconductor chip. More specifically, the adhesive sheet disclosed herein can be used as a temporary fixing material for a semiconductor chip when the semiconductor chip is arranged on the first adhesive layer of the adhesive sheet, the semiconductor chip is covered with an encapsulation resin (usually an epoxy resin), and the encapsulation resin is cured to encapsulate the semiconductor chip. After the semiconductor chip is encapsulated, the adhesive sheet can be peeled off from the structure including the encapsulation resin and the semiconductor chip during a predetermined post-process (for example, back grinding of the encapsulation resin, pattern formation, bump formation, chipping (cutting)). The epoxy equivalent of the encapsulation resin is, for example, 50 g/eq to 500 g/eq.

Figure 1 is a schematic cross-sectional view showing one embodiment of the adhesive sheet disclosed herein. The adhesive sheet 100 comprises a substrate 10 and a first adhesive layer 20 disposed on one side of the substrate 10. The adhesive sheet 100 further comprises a second adhesive layer 30 on the back side of the substrate 10 (the side opposite to the first adhesive layer 20). That is, the adhesive sheet 100 comprises the first adhesive layer 20, the substrate 10, and the second adhesive layer 30, in this order.

The adhesive sheet 100 can be used for resin sealing of semiconductor chips, for example, as shown in FIG. 2. First, a plurality of semiconductor chips 1 are attached onto the first adhesive layer of the adhesive sheet 100 (step (i)). Next, the semiconductor chips 1 are covered with a semi-cured product 2' of the sealing resin (step (ii)), and the semi-cured product 2' is cured to seal the semiconductor chips 1 with the sealing resin 2 (step (iii)). The semi-cured product 2' can be formed, for example, using a composition containing a naphthalene-type bifunctional epoxy resin (epoxy equivalent: 144). Then, during a specified post-process, the adhesive sheet 100 is peeled off from the structure 50 containing the semiconductor chips 1 and the sealing resin 2 (step (iv)).

In this resin sealing process, if a conventional adhesive sheet 900 is used as shown in FIG. 3, component migration occurs between the first adhesive layer and the sealing resin in steps (ii) and (iii), and a mixed phase of the adhesive component and the sealing resin component is formed. The formation of the mixed phase can be understood as, for example, swelling of the adhesive layer due to migration of the sealing resin component. When the adhesive sheet 900 is peeled off, if such a mixed phase is peeled off together with the adhesive sheet 900 (step (iv)), a structure 50 with a step (standoff) between the semiconductor chip 1 and the sealing resin 2 is formed.

In the adhesive sheet 100 disclosed herein, the thickness of the first adhesive layer 20 is 20 μm or more, so that the components that migrate from the sealing resin 2 to the first adhesive layer 20 diffuse into the first adhesive layer 20 and become low in concentration overall. Therefore, the concentration of the migration components on the surface of the first adhesive layer 20 decreases, and adhesive residue caused by the migration components from the adherend side is unlikely to occur on the surface of the first adhesive layer 20. In addition, since the thickness of the first adhesive layer 20 is 70 μm or less, adhesive residue due to cohesive failure of the first adhesive layer 20 is unlikely to occur. The first adhesive layer 20 can be well adhered to the semiconductor chip 1, which is the adherend. Furthermore, in the first adhesive layer 20, the thickness of the mixed phase of the adhesive component and the sealing resin component formed on the surface of the first adhesive layer 20 is reduced due to the low concentration of the migration components, and the step between the semiconductor chip 1 and the sealing resin 2, which depends on the thickness of the mixed phase, can be suppressed. Furthermore, since the thickness of the first adhesive layer 20 is 20 μm or more, the first adhesive layer 20 can conform well to the surface shape of the adherend (for example, steps due to metal wiring that may exist on the adhesive layer side surface of the semiconductor chip 1), and the occurrence of a defect (mold flash) in which the sealing resin 2 penetrates into the interface between the adhesive sheet 100 and the semiconductor chip 1 can be prevented. Therefore, the adhesive sheet 100 is particularly suitable for the resin sealing process of semiconductor chips.

In addition, by providing the second adhesive layer 30, when resin sealing is performed on the carrier, the adhesive sheet 100 can be easily fixed to the carrier by attaching the second adhesive layer 30 side to the carrier. Furthermore, at least the surface of the second adhesive layer 30 is composed of an adhesive containing heat-expandable microspheres. When such an adhesive containing heat-expandable microspheres is heated to a predetermined temperature or higher, the heat-expandable microspheres are expanded to generate unevenness on the surface of the adhesive layer, and the adhesive force can be reduced or eliminated. By constituting at least the surface of the second adhesive layer 30 with an adhesive containing heat-expandable microspheres, the necessary adhesiveness is expressed when the adhesive sheet 100 is fixed (for example, fixed to a carrier) via the second adhesive layer 30, and when the adhesive sheet 100 is peeled off (for example, when peeled off from the carrier), the adhesive force is reduced or eliminated by heating, thereby exhibiting good peelability. An elastic intermediate layer (which may be an adhesive layer) that does not contain heat-expandable microspheres or contains a small amount of heat-expandable microspheres may be disposed between the adhesive layer containing heat-expandable microspheres and the substrate 10.

<First Pressure-Sensitive Adhesive Layer>
In the pressure-sensitive adhesive sheet disclosed herein, any suitable pressure-sensitive adhesive may be used as the pressure-sensitive adhesive constituting the first pressure-sensitive adhesive layer disposed on one side of the substrate, as long as the effects of the present invention can be obtained. The pressure-sensitive adhesive layer may contain one or more types of pressure-sensitive adhesive selected from various known pressure-sensitive adhesives, such as acrylic pressure-sensitive adhesives, rubber pressure-sensitive adhesives (natural rubber, synthetic rubber, a mixture of these, etc.), silicone pressure-sensitive adhesives, polyester pressure-sensitive adhesives, urethane pressure-sensitive adhesives, polyether pressure-sensitive adhesives, polyamide pressure-sensitive adhesives, and fluorine pressure-sensitive adhesives.

Although not particularly limited, the effects of the present invention are preferably realized when the first adhesive layer has a single-layer structure containing one type of adhesive. Since such a first adhesive layer is made of a homogeneous single layer of adhesive, the components that migrate from the adherend are well, preferably evenly, dispersed within the layer, and the concentration of the migrating components on the surface of the first adhesive layer is likely to decrease, making it possible to preferably suppress the occurrence of adhesive residue on the surface of the first adhesive layer caused by the components that migrate from the adherend.

(thickness)
The thickness of the first adhesive layer is 20 μm or more and 70 μm or less. By setting the thickness of the first adhesive layer within the range of 20 μm or more and 70 μm or less, it is possible to adhere well to the adherend, and to exhibit good adhesive residue prevention when peeled off from the adherend. For example, when the adhesive sheet is used in a resin sealing process of a semiconductor chip, it is possible to achieve both good chip retention and prevention of adhesive residue caused by the sealing resin. In addition, in such an application, the above-mentioned configuration can reduce the step between the semiconductor chip and the sealing resin. That is, it is possible to achieve both semiconductor chip retention and step reduction, more specifically, to achieve both chip shift prevention and standoff reduction. Furthermore, since the first adhesive layer has a sufficient thickness, it is easy to exhibit good conformability to the surface shape of the adherend. In some embodiments, from the viewpoints of preventing glue residue caused by migrating components, reducing steps, conforming to surface shape, etc., the thickness of the first pressure-sensitive adhesive layer may be 25 μm or more, 35 μm or more, 45 μm or more, 55 μm or more, or 65 μm or more. Also, in some embodiments, from the viewpoints of preventing glue residue due to cohesive failure of the first pressure-sensitive adhesive layer, etc., the thickness of the first pressure-sensitive adhesive layer may be 60 μm or less, 50 μm or less, 40 μm or less, or 30 μm or less.

(FT-IR Spectral Characteristics)
In some embodiments, the first pressure-sensitive adhesive layer has an increase in peak intensity derived from the epoxy resin before and after the epoxy resin treatment of the surface of the first pressure-sensitive adhesive layer, which is determined based on the peak intensity present in the range of 1725 cm ^-1 to 1750 cm ^-1 in the FT-IR spectrum at a measurement position (hereinafter also simply referred to as "measurement position A") located at a depth of 5 μm from the substrate side of the first pressure-sensitive adhesive layer, of 0.030 or less. By limiting the increase in peak intensity derived from the epoxy resin to 0.030 or less, for example, in an embodiment in which the pressure-sensitive adhesive sheet is used in a resin sealing process of a semiconductor chip, the migration component from the epoxy sealing resin in the first pressure-sensitive adhesive layer is suppressed to a predetermined amount or less, and adhesive residue due to the migration component from the adherend side is unlikely to occur on the surface of the first pressure-sensitive adhesive layer. In addition, when the pressure-sensitive adhesive sheet is used in a resin sealing process of a semiconductor chip, the step between the semiconductor chip and the sealing resin tends to be further reduced.

More specifically, the above-mentioned peak intensity increase amount A is calculated by determining the ratio A0 of the peak intensity attributable to the epoxy resin to the peak intensity in the range of 1725 cm ^-1 to 1750 cm ^-1 in the FT-IR spectrum of the first pressure-sensitive adhesive layer at measurement position A before the specified epoxy-based resin treatment, and the ratio A1 of the peak intensity attributable to the epoxy resin to the peak intensity in the range of 1725 cm ^-1 to 1750 cm ^-1 in the FT-IR spectrum of the first pressure-sensitive adhesive layer at measurement position A after the specified epoxy-based resin treatment, and calculating the difference between them (A1-A0).

As the peak intensity derived from the epoxy resin, a peak intensity present in the range of 1505 cm ^-1 to 1515 cm ^-1 is used because the epoxy resin used in the epoxy resin treatment contains an aromatic ring. In the FT-IR spectrum, the range of 1505 cm ^-1 to 1515 cm ^-1 is an absorption band based on the stretching vibration within the aromatic ring plane. In the FT-IR spectrum, the range of 1725 cm ^-1 to 1750 cm ^-1 , which is the absorption band of the peak intensity serving as the basis for calculating the amount of increase in peak intensity, is an absorption band based on the stretching vibration of ester C=O.

In addition, when the first pressure-sensitive adhesive layer does not contain an aromatic ring or contains only a small amount of an aromatic ring, no peak is observed in the range of 1505 cm ^-1 to 1515 cm ^-1 in the FT-IR spectrum at measurement position A before the epoxy-based resin treatment, or the height of the peak may be negligible without substantially affecting the peak intensity increase amount A. In that case, the peak intensity present in the range of 1505 cm ^-1 to 1515 cm ^-1 in the FT-IR spectrum at measurement position A before the epoxy-based resin treatment (the above-mentioned peak intensity ratio A0) may be regarded as zero, and the peak intensity derived from the epoxy-based resin at measurement position A after the epoxy-based resin treatment (the above-mentioned peak intensity ratio A1) may be regarded as the peak intensity increase amount A.

The epoxy resin treatment on the surface of the first adhesive layer is a process in which a standard epoxy resin containing an aromatic ring is used, and the surface is molded at a temperature of 145°C, pressure conditions of 0.2 MPa, and heating and pressure time of 400 seconds, followed by heating at 150°C for 4 hours to harden the sealing resin. More specifically, the process is carried out as described in the Examples below.

In some preferred embodiments, from the viewpoint of obtaining better adhesive transfer prevention, the peak strength increase amount A is 0.025 or less, may be 0.020 or less, may be 0.015 or less, or may be 0.010 or less. By limiting the peak strength increase amount A to a predetermined value or less, the adhesion (anchoring property) between the first adhesive layer and the substrate tends to be maintained well, and anchor failure tends to be less likely to occur. In addition, when the adhesive sheet is used in a resin sealing process for a semiconductor chip, the step between the semiconductor chip and the sealing resin tends to be further reduced. The lower limit value of the peak strength increase amount A is 0.000 or more, may be greater than 0.000, may be 0.001 or more, and may be approximately 0.003 or more (e.g., 0.005 or more) in practical use.

Although not particularly limited, in some embodiments, the first pressure-sensitive adhesive layer has a ratio of a peak intensity present in the range of 1700 cm ^-1 to 1710 cm ^-1 to a peak intensity present in the range of 1725 cm ^-1 to 1750 cm ^-1 in an FT-IR spectrum (hereinafter, also simply referred to as "peak intensity ratio B") of about 0.050 or less, suitably 0.40 or less, preferably 0.325 or less, and more preferably 0.300 or less. In the above FT-IR spectrum, the range of 1700 cm ^-1 to 1710 cm ^-1 is an absorption band based on the carboxylic acid C=O stretching vibration, and the peak intensity present in the above range is a peak intensity derived from carboxylic acid. By having the peak intensity ratio B be a predetermined value or less, for example, in an embodiment in which a pressure-sensitive adhesive sheet is used in a resin sealing process of a semiconductor chip, the amount of a component that has migrated from the sealing resin to the first pressure-sensitive adhesive layer that is attracted to a carboxylic acid (which may be in the form of a carboxyl group in a polymer) is limited in the surface layer portion of the first pressure-sensitive adhesive layer. As a result, the adhesive is well dispersed throughout the first pressure-sensitive adhesive layer and is not easily unevenly distributed on the surface of the first pressure-sensitive adhesive layer. This tends to make it more difficult for adhesive residue to occur on the surface of the first pressure-sensitive adhesive layer due to the migration component from the adherend side. In addition, the step between the semiconductor chip and the sealing resin tends to be further reduced. By having the peak intensity ratio B be equal to or less than a predetermined value, the adhesion (anchor property) between the first pressure-sensitive adhesive layer and the substrate is well maintained, and anchor failure tends to be more unlikely to occur. In addition, in some embodiments, the peak intensity ratio B may be 0.010 or more, 0.050 or more, 0.100 or more, 0.150 or more, 0.200 or more, or 0.250 or more from the viewpoint of obtaining properties based on the inclusion of carboxylic acid (specifically, adhesive properties).

Although not particularly limited, in some embodiments, the first pressure-sensitive adhesive layer may have a ratio of a peak intensity present in the range of 2955 cm ^-1 to 2965 cm ^-1 to a peak intensity present in the range of 1725 cm ^-1 to 1750 cm ^-1 in an FT-IR spectrum (hereinafter, also simply referred to as "peak intensity ratio C") of 0.100 or more, 0.120 or more, or 0.130 or more. In the FT-IR spectrum, the range of 2955 cm ^-1 to 2965 cm ^-1 is an absorption band based on C-H stretching vibration. The larger the peak intensity ratio C, the longer the side chain of the polymer present in the first pressure-sensitive adhesive layer tends to be. For example, in an embodiment in which a pressure-sensitive adhesive sheet is used in a resin sealing process of a semiconductor chip, the amount of components transferred from the sealing resin to the first pressure-sensitive adhesive layer is easily suppressed, and adhesive residue caused by the transferred components on the surface of the first pressure-sensitive adhesive layer tends to be less likely to occur. In some embodiments, the peak intensity ratio C may be 0.300 or less, 0.200 or less, or 0.150 or less. When the peak intensity ratio C is a predetermined value or less, the components that have migrated from the sealing resin to the surface of the first adhesive layer are likely to diffuse from the surface of the first adhesive layer to the entire surface. When the peak intensity ratio C is within the above range, the polarity of the first adhesive layer is appropriately maintained, so that adhesion between the first adhesive layer and the substrate is easily obtained and anchor failure is less likely to occur. In addition, when the adhesive sheet is used in a resin sealing process of a semiconductor chip, the step between the semiconductor chip and the sealing resin tends to be further reduced.

The above peak intensity increase amount A and peak intensity ratios B and C are specifically measured by the method described in the Examples below.

The above peak intensity increase amount A and peak intensity ratios B and C can be adjusted and set by setting the thickness of the first adhesive layer within the range of 20 to 70 μm, and by adjusting the monomer composition of the polymer contained in the first adhesive layer (e.g., selection of the main monomer type, selection of the carboxyl group-containing monomer type, their polymerization ratio, etc.) and the contained components (crosslinking agent type, etc.).

(Adhesive properties)
Although not particularly limited, in some embodiments, the first pressure-sensitive adhesive layer has an adhesion to epoxy resin (adhesion to epoxy resin) measured at 100° C. after the surface of the first pressure-sensitive adhesive layer is treated with an epoxy resin, and the adhesion to epoxy resin is in the range of 0.01 N/10 mm or more and 3.00 N/10 mm or less. According to a pressure-sensitive adhesive sheet in which the adhesion to epoxy resin of the first pressure-sensitive adhesive layer is in the above range, for example, in an embodiment in which the pressure-sensitive adhesive sheet is used in a resin sealing process of a semiconductor chip, the first pressure-sensitive adhesive layer adheres well to the sealing resin while being less likely to leave adhesive residue when peeled off from the sealing resin. The adhesion to epoxy resin is suitably 0.10 N/10 mm or more, preferably 0.30 N/10 mm or more, and may be 0.50 N/10 mm or more. From the viewpoint of preventing adhesive residue, the adhesion to the epoxy resin is preferably 2.00 N/10 mm or less, more preferably 1.50 N/10 mm or less, may be 1.00 N/10 mm or less, may be 0.80 N/10 mm or less, or may be 0.60 N/10 mm or less. The adhesion to the epoxy resin is measured based on the description of the adhesion to the sealing resin in the examples described later.

Although not particularly limited, in some embodiments, the first adhesive layer has an adhesive strength (adhesive strength against PET) against a polyethylene terephthalate film measured under an environment of 23°C and 50% RH of 1.00 N/20 mm or more and 10.0 N/20 mm or less. According to an adhesive sheet in which the adhesive strength against PET of the first adhesive layer is within the above range, the first adhesive layer can preferably fix an adherend (e.g., a semiconductor chip), and adhesive residue is unlikely to be left on the adherend when the first adhesive layer side of the adhesive sheet is peeled off from the adherend. In applications for resin sealing processes of semiconductor chips, chip shift can be preferably prevented. In some preferred embodiments, the adhesive strength against PET may be 2.00 N/20 mm or more, suitably 3.00 N/20 mm or more, preferably 4.00 N/20 mm or more, and more preferably 5.00 N/20 mm or more (e.g., more than 5.00 N/20 mm) from the viewpoint of preferably fixing an adherend (e.g., a semiconductor chip). In some embodiments, from the viewpoint of preventing damage to the adherend due to the load when peeling off the pressure-sensitive adhesive sheet, the adhesive strength to PET may be 9.00 N/20 mm or less, 7.00 N/20 mm or less, 5.00 N/20 mm or less, or 3.00 N/20 mm or less. The adhesive strength to PET is measured by the method described in the Examples below.

(Storage Modulus)
Although not particularly limited, in some embodiments, the first pressure-sensitive adhesive layer may have a storage modulus at 23 ° C. in the range of, for example, 0.05 MPa or more and 1.00 MPa or less, preferably 0.10 MPa or more and 0.50 MPa or less. A pressure-sensitive adhesive having a storage modulus at 23 ° C. in the above range has moderate flexibility and elasticity, and is easy to achieve both adhesion to the adherend and prevention of adhesive residue. The above-mentioned 23 ° C. storage modulus may be 0.15 MPa or more from the viewpoint of improving the prevention of adhesive residue. In some preferred embodiments, the above-mentioned 23 ° C. storage modulus may be 0.40 MPa or less, 0.30 MPa or less, or 0.20 MPa or less from the viewpoint of conformity to the surface shape of the adherend. The storage modulus at 23 ° C. of the first pressure-sensitive adhesive layer is measured by the method described in the Examples below.

(Acrylic polymer)
The first pressure-sensitive adhesive layer preferably contains an acrylic pressure-sensitive adhesive having an acrylic polymer as a base polymer. The acrylic polymer, which is the base polymer of the acrylic pressure-sensitive adhesive, is preferably a polymer of monomer components that contain an alkyl (meth)acrylate as a main monomer and may further contain a sub-monomer copolymerizable with the main monomer as necessary. Here, the main monomer refers to the main component in the monomer components that constitute the acrylic polymer, i.e., a component that is contained in the monomer components in an amount of more than 50% by weight.

As the alkyl (meth)acrylate, for example, a compound represented by the following formula (A) can be suitably used.
_CH2 =C( ^R1 ) ^COOR2 (A)
Here, R ¹ in the above formula (A) is a hydrogen atom or a methyl group. R ² is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, such a range of the number of carbon atoms may be expressed as "C _1-20 "). From the viewpoint of ease of adjusting the adhesive properties, etc., alkyl (meth)acrylates in which R ² is a chain alkyl group of _1-18 are preferred, and alkyl (meth)acrylates in which R ² is a chain alkyl group of _1-12 are more preferred. The above alkyl (meth)acrylates can be used alone or in combination of two or more.

Specific examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isopropyl (meth)acrylate. Examples of the (meth)acrylic acid C 1-20 alkyl ester include octyl, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. In some embodiments, it is preferable to use _{a (meth)acrylic acid alkyl ester having a C 1-6 (} preferably C _1-5 , more preferably C _1-4 ) linear or branched alkyl group (e.g., butyl (meth)acrylate). In some embodiments, it is more preferable to use a (meth)acrylic acid alkyl ester having a C _1-3 (more preferably C _1-2 ) linear or branched alkyl group (e.g., methyl (meth)acrylate or ethyl (meth)acrylate). In some embodiments, it is more preferable to use a (meth)acrylic acid alkyl ester having a C _7-20 (more preferably C _7-18 , even more preferably C _8-12 ) linear or branched alkyl group (e.g., 2-ethylhexyl (meth)acrylate). In some preferred embodiments, a (meth)acrylic acid alkyl ester having a C _1-6 (preferably C _1-5 , more preferably C _1-4 ) linear or branched alkyl group and a (meth)acrylic acid alkyl ester having a C _7-20 (more preferably C _7-18 , even more preferably C _8-12 ) linear or branched alkyl group are used in combination.

In some embodiments, 30% by weight or more of the monomer components constituting the acrylic polymer is an alkyl (meth)acrylate having a structure in which R ² in the above formula (A) is a chain alkyl group having 1 to 20 carbon atoms (i.e., an alkyl (meth)acrylate having a chain alkyl group of _1-20 carbon atoms). By using a predetermined amount or more of the above alkyl (meth)acrylate, it is easy to realize the desired adhesive properties (adhesive strength, etc.). From this viewpoint, the content of the above alkyl (meth)acrylate in the monomer components used in the synthesis of the acrylic polymer is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and may be 90% by weight or more. In addition, the content of the above alkyl (meth)acrylate in the monomer components is suitably 99% by weight or less, and preferably 95% by weight or less, from the viewpoint of effectively obtaining the effect (e.g., cohesive strength) due to copolymerization of the sub-monomer.

In some embodiments, 10% by weight or more of the monomer components constituting the acrylic polymer are alkyl (meth)acrylates (i.e., (meth)acrylic acid alkyl esters having a C _1-6 linear or branched alkyl group) in which R ² in the above formula (A) is a linear or branched alkyl group having 6 or less carbon atoms (preferably 1 to 5, more preferably 1 to 4). By using an acrylic polymer having the above monomer composition, the polarity of the first adhesive layer is appropriately maintained, and an adhesive having good adhesion to an adherend or a substrate is easily obtained. In addition, since an acrylic polymer having the above monomer composition has a predetermined number or more of relatively short side chains, by using such an acrylic polymer in the first adhesive layer, for example, in an embodiment in which an adhesive sheet is used in a resin sealing process of a semiconductor chip, the components that have migrated from the sealing resin to the first adhesive layer are likely to diffuse from the surface layer of the first adhesive layer to the entirety. In addition, when an adhesive sheet is used in a resin sealing process of a semiconductor chip, the step between the semiconductor chip and the sealing resin tends to be further reduced. In some preferred embodiments, from the viewpoint of improving adhesion to an adherend, the content of the (meth)acrylic acid alkyl ester having the above-mentioned C _1-6 (preferably C _1-5 , more preferably C _1-4 ) linear or branched alkyl group in the monomer component used in the synthesis of the acrylic polymer is suitably 30% by weight or more, may be 40% by weight or more, may be 50% by weight or more, or may be 60% by weight or more. In addition, the upper limit of the content of the (meth)acrylic acid alkyl ester having the above-mentioned C _1-6 (preferably C _1-5 , more preferably C _1-4 ) linear or branched alkyl group in the monomer component is not particularly limited, but may be, for example, 90% by weight or less, suitably 80% by weight or less, preferably 70% by weight or less, and in some embodiments, may be 50% by weight or less, 30% by weight or less, or may be 20% by weight or less. By using an appropriate amount of the (meth)acrylic acid alkyl ester, the glass transition temperature of the acrylic polymer can be set to an appropriate range that can favorably achieve both adherend adhesion and adhesive residue prevention. In addition, the acrylic polymer having the above monomer composition has a relatively short side chain limited to a predetermined number or less, so that the polarity is appropriately controlled, and for example, in an embodiment in which an adhesive sheet is used in a resin sealing process of a semiconductor chip, component migration from the sealing resin to the first adhesive layer is suppressed, and adhesive residue caused by components migrating from the adherend side tends to be less likely to occur on the surface of the first adhesive layer. The (meth)acrylic acid alkyl ester having a _{C 1-6} linear or branched alkyl group can be used alone or in combination of two or more.

In some embodiments, 10% by weight or more of the monomer components constituting the acrylic polymer is an alkyl (meth)acrylate (i.e., a (meth)acrylic acid alkyl ester having a C _1-3 linear or branched alkyl group) having a structure in which R ² in the above formula (A) is a linear or branched alkyl group having 3 or less carbon atoms (preferably 1 or 2). By using such an alkyl (meth)acrylate, the polarity of the first pressure-sensitive adhesive layer is appropriately maintained, and good adhesion to the adherend is easily obtained. In addition, by using an acrylic polymer having the above monomer composition for the first pressure-sensitive adhesive layer, for example, in an embodiment in which a pressure-sensitive adhesive sheet is used in a resin sealing process of a semiconductor chip, the components that have migrated from the sealing resin to the first pressure-sensitive adhesive layer are likely to diffuse from the surface layer of the first pressure-sensitive adhesive layer to the entirety. In addition, in such applications, the step between the semiconductor chip and the sealing resin tends to be further reduced. In some preferred embodiments, from the viewpoint of improving adhesion to an adherend, the content of the (meth)acrylic acid alkyl ester having the above-mentioned C _1-3 (preferably C _1-2 ) linear or branched alkyl group in the monomer component used in the synthesis of the acrylic polymer is suitably 30% by weight or more, preferably 40% by weight or more, and in some embodiments may be 50% by weight or more or may be 60% by weight or more. The upper limit of the content of the (meth)acrylic acid alkyl ester having the above-mentioned C _1-3 (preferably C _1-2 ) linear or branched alkyl group in the monomer component is not particularly limited, but is suitably, for example, 99% by weight or less, preferably 90% by weight or less, more preferably 80% by weight or less, and even more preferably 70% by weight or less, and in some embodiments may be 50% by weight or less, 30% by weight or less, or 20% by weight or less. By using an appropriate amount of the above (meth)acrylic acid alkyl ester, the glass transition temperature of the acrylic polymer can be set within an appropriate range that satisfies both the adhesion to the adherend and the resistance to adhesive transfer. The (meth)acrylic acid alkyl ester having a _C1-3 linear or branched alkyl group can be used alone or in combination of two or more.

In some embodiments, 10% by weight or more of the monomer components constituting the acrylic polymer is an alkyl (meth)acrylate (i.e., a (meth)acrylic acid alkyl ester having a C 7 or more linear or branched alkyl group) having a structure in which R ² in the above formula (A) is a linear or branched alkyl group having _{7 or more} carbon atoms (e.g., 8 or more; also preferably 18 or less, e.g., 12 or less, more preferably 8 or less). By using such an alkyl (meth)acrylate, component migration between the pressure-sensitive adhesive layer and the sealing resin can be preferably suppressed. The content of the (meth)acrylic acid alkyl ester having a C _{7 or more} linear or branched alkyl group (more preferably C _7-18 , even more preferably C _8-12 ) in the monomer components used in the synthesis of the acrylic polymer is preferably 20% by weight or more, and in some embodiments, may be 30% by weight or more, 50% by weight or more, or 70% by weight or more. The content of the (meth)acrylic acid alkyl ester having a linear or branched alkyl group of C7 _{or more} (more preferably _C7-18 , even more preferably _C8-12 ) in the monomer component is suitably 90% by weight or less, preferably 70% by weight or less, may be 50% by weight or less, or may be 30% by weight or less, from the viewpoint of obtaining good adhesion to adherends and prevention of adhesive transfer. The (meth)acrylic acid alkyl ester having a linear or branched alkyl group of _{C7 or more} may be used alone or in combination of two or more.

The secondary monomer that is copolymerizable with the main monomer, alkyl (meth)acrylate, can be useful for introducing crosslinking points into the acrylic polymer and for increasing the cohesive strength and heat resistance of the acrylic polymer. It can also be useful for satisfying the FT-IR spectrum characteristics of the first adhesive layer (e.g., peak intensity increase amount A, peak intensity ratio B). As the secondary monomer, for example, the following functional group-containing monomers can be used alone or in combination of two or more. For example, the following functional group-containing monomers can be used alone or in combination of two or more.

Carboxy group-containing monomers, such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid;
Acid anhydride monomers such as maleic anhydride and isotonic anhydride;
Hydroxy group-containing monomers, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl methacrylate;
(N-substituted) amide monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, and N-methylolpropane(meth)acrylamide;
Monomers having a nitrogen atom-containing ring, such as N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-(meth)acryloylmorpholine;
Amino group-containing monomers, such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate;
Epoxy group-containing acrylic monomers, such as glycidyl (meth)acrylate;
Cyano group-containing monomers such as acrylonitrile and methacrylonitrile;
Sulfonic acid group-containing monomers, such as styrenesulfonic acid, allylsulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid;
Maleimide monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide;
Itaconimide monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, and N-laurylitaconimide;
Succinimide monomers such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, and N-(meth)acryloyl-8-oxyoctamethylene succinimide;
Alkoxysilyl group-containing monomers, such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane.

The monomer component may contain, as a secondary monomer, one or more copolymerizable monomers other than the functional group-containing monomers exemplified above, for the purpose of improving cohesive strength, etc. Examples of such other copolymerizable monomers include vinyl ester monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrenes (α-methylstyrene, etc.), and vinyl toluene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate). acrylates; olefin-based monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether-based monomers such as methyl vinyl ether and ethyl vinyl ether; glycol-based monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate;
Other examples include heterocycle-containing monomers such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylates, silicone (meth)acrylates, and the like.

The monomer component may contain a polyfunctional monomer for the purpose of crosslinking or the like as the other copolymerizable monomer. Non-limiting examples of such polyfunctional monomers include hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, polyfunctional epoxy acrylate, polyfunctional polyester acrylate, polyfunctional urethane acrylate, and the like. The polyfunctional monomers may be used alone or in combination of two or more.

In some preferred embodiments, the acrylic polymer preferably contains a structural unit a derived from a monomer having a homopolymer glass transition temperature (Tg) of -5°C to 150°C (preferably 50°C to 150°C, more preferably 80°C to 120°C). The content of the structural unit a is preferably 0.1% by weight to 20% by weight, more preferably 1% by weight to 15% by weight, particularly preferably 1.5% by weight to 10% by weight, and most preferably 3% by weight to 10% by weight, based on the total structural units constituting the acrylic polymer.

Examples of monomers having a homopolymer Tg of -5°C to 150°C include 2-hydroxyethyl acrylate (Tg: -3°C), 2-hydroxyethyl methacrylate (Tg: 77°C), acrylic acid (Tg: 102°C), cyclohexyl methacrylate (Tg: 83°C), dicyclopentanyl acrylate (Tg: 120°C), dicyclopentanyl methacrylate (Tg: 175°C), isobornyl acrylate (Tg: 94°C), isobornyl methacrylate (Tg: 150°C), t-butyl methacrylate (Tg: 118°C), methyl methacrylate (Tg: 105°C), styrene (Tg: 80°C), acrylonitrile (Tg: 97°C), and N-acryloylmorpholine (Tg: 145°C). For the glass transition temperature of homopolymers of monomers other than those mentioned above, values described in publicly available documents such as "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989) are used. For monomers for which multiple values are described in the Polymer Handbook, the highest value is adopted. If the Tg of the homopolymer is not described in publicly available documents, the value obtained by the measurement method described in JP-A-2007-51271 is used.
These monomers may be used alone or in combination of two or more. Among them, methyl methacrylate is preferred in the case of improving the visibility of the adherend during processing, since it enhances the transparency of the pressure-sensitive adhesive layer.

In some embodiments, the acrylic polymer may contain a structural unit derived from a carboxyl group-containing monomer, but the content is preferably limited. The content of the structural unit derived from the carboxyl group-containing monomer is suitably 10% by weight or less, preferably 7% by weight or less, more preferably 5% by weight or less, even more preferably 3% by weight or less, and particularly preferably 1% by weight or less, based on the total structural units constituting the acrylic polymer. By limiting the structural unit derived from the carboxyl group-containing monomer in the acrylic polymer, the FT-IR spectrum characteristics (e.g., peak intensity increase amount A, peak intensity ratio B) of the first adhesive layer can be preferably satisfied, and good adhesive transfer prevention properties and step reduction properties are easily obtained. From such a viewpoint, in some preferred embodiments, the content of the structural unit derived from the carboxyl group-containing monomer is less than 1% by weight, and may be less than 0.1% by weight, based on the total structural units constituting the acrylic polymer, and the acrylic polymer may not contain a structural unit derived from a carboxyl group-containing monomer. In an embodiment in which the acrylic polymer contains a structural unit derived from a carboxyl group-containing monomer, from the viewpoint of obtaining the effects of containing the structural unit derived from the carboxyl group-containing monomer (cohesive strength, adhesive strength, etc.), the content of the structural unit derived from the carboxyl group-containing monomer may be 0.1% by weight or more, 1% by weight or more, or 3% by weight or more.

In some preferred embodiments, the acrylic polymer contains a constituent unit derived from a hydroxyl group-containing monomer. The content of the constituent unit derived from a hydroxyl group-containing monomer is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and even more preferably 1% by weight or more, for example 3% by weight or more, and is preferably 20% by weight or less, more preferably 10% by weight or less, for example 7% by weight or less, based on the total constituent units constituting the acrylic polymer.

The weight average molecular weight (Mw) of the acrylic polymer is, for example, a standard polystyrene-equivalent weight average molecular weight (Mw) obtained by GPC (gel permeation chromatography) of about 10 × 10 ⁴ or more, preferably about 30 × 10 ⁴ or more, may be about 45 × 10 ⁴ or more, or may be 50 × 10 ⁴ or more. The upper limit of the Mw is not particularly limited, and is, for example, about 300 × 10 ⁴ or less, and from the viewpoint of adhesive strength, coatability when forming the adhesive layer, etc., it is preferably about 100 × 10 ⁴ or less, and may be about 70 × 10 ⁴ or less.

Specifically, the Mw of the acrylic polymer can be determined by measuring under the following conditions using a GPC measuring device (trade name: "HLC-8220GPC" manufactured by Tosoh Corporation). The same applies to the examples described later.
[GPC measurement conditions]
Sample concentration: 1.0 g/L (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: tetrahydrofuran (THF)
Flow rate (flow rate): 0.5 mL/min Column temperature (measurement temperature): 40° C.
Column: Tosoh Corporation, product name "TSKgel GMH-H(S)" x 2
Column size: 7.8 mm ID x 300 mm
Detector: differential refractometer (RI)
Standard sample: polystyrene After preparation, the sample is left to stand overnight and filtered through a 0.45 μm membrane filter before use.

(Crosslinking Agent)
In some embodiments, the adhesive composition for forming the first adhesive layer preferably contains a crosslinking agent in addition to the base polymer. By including a crosslinking agent, the cohesive strength of the first adhesive layer can be improved. For example, the base polymer contained in the first adhesive layer is preferably crosslinked by a crosslinking agent in the adhesive constituting the first adhesive layer. For example, by using an adhesive composition containing a base polymer and a suitable crosslinking agent, a first adhesive layer can be obtained that is composed of an adhesive in which the base polymer is crosslinked by the crosslinking agent.

The type of crosslinking agent is not particularly limited, and may be appropriately selected from, for example, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, amine-based crosslinking agents, etc. The crosslinking agents may be used alone or in combination of two or more. Among them, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred.

Specific examples of isocyanate-based crosslinking agents include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; tolylene diisocyanate (for example, Mitsui Chemicals, product name "Takenate D-101E"), 4,4'-diphenylmethane diisocyanate, xylitol, Examples of the isocyanate adduct include aromatic isocyanates such as diisocyanate; trimethylolpropane/tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, product name "Coronate L"), trimethylolpropane/hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, product name "Coronate HL"), and isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, product name "Coronate HX"); and the like. The amount of the isocyanate-based crosslinking agent used can be set to any appropriate amount depending on the desired adhesive strength. In some embodiments, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the base polymer is typically 0.1 parts by weight or more and 20 parts by weight or less, and preferably 1 part by weight or more and 10 parts by weight or less.

Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "Tetrad C"), 1,6-hexanediol diglycidyl ether (manufactured by Kyoeisha Chemical Company, Inc., product name "Epolight 1600"), neopentyl glycol diglycidyl ether (manufactured by Kyoeisha Chemical Company, Inc., product name "Epolight 1500NP"), ethylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Company, Inc., product name "Epolight 40E"), propylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Company, Inc., product name "Epolight 70P"), polyethylene glycol diglycidyl ether (manufactured by Nippon Oil & Fats Co., Ltd., product name "Epiol E-400"), polypropylene ... Yushi Co., Ltd., trade name "Epiol P-200"), sorbitol polyglycidyl ether (Nagase ChemteX Corporation, trade name "Denacol EX-611"), glycerol polyglycidyl ether (Nagase ChemteX Corporation, trade name "Denacol EX-314"), pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether (Nagase ChemteX Corporation, trade name "Denacol EX-512"), sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, epoxy resins having two or more epoxy groups in the molecule, etc. The amount of epoxy crosslinking agent used can be set to any appropriate amount depending on the desired properties. In some embodiments, the amount of epoxy crosslinking agent used relative to 100 parts by weight of the base polymer may be, for example, 0.01 parts by weight or more and 50 parts by weight or less, preferably 0.6 parts by weight or more and 15 parts by weight or less, more preferably 2 parts by weight or more and 13 parts by weight or less, and even more preferably 3 parts by weight or more and 10 parts by weight or less.

In some embodiments, an isocyanate-based crosslinking agent may be preferably used as the crosslinking agent used in the first adhesive layer. By using an isocyanate-based crosslinking agent, an adhesive layer having good cohesive strength can be formed, and while having the desired adhesion and adhesive strength, it is possible to effectively prevent adhesive residue caused by cohesive failure. For example, in an embodiment in which an acrylic polymer having a hydroxy group is used as the base polymer of the first adhesive layer, an isocyanate-based crosslinking agent may be preferably used.

In some other embodiments, an epoxy-based crosslinking agent may be used as the crosslinking agent for the first adhesive layer. For example, in an embodiment in which an acrylic polymer having a carboxy group is used as the base polymer of the first adhesive layer, an epoxy-based crosslinking agent can be used to form a desired crosslinked structure in the first adhesive layer while reducing the amount of carboxylic acid in the first adhesive layer. This allows the FT-IR spectrum characteristics (e.g., peak intensity increase amount A, peak intensity ratio B) of the first adhesive layer to be preferably satisfied. A first adhesive layer having a crosslinked structure in which the base polymer is crosslinked with an epoxy-based crosslinking agent can form an adhesive layer with high cohesive strength, and can effectively prevent glue residue due to cohesive failure.

In some embodiments, a crosslinking agent containing a nitrogen (N) atom may be preferably used as the crosslinking agent. Crosslinking agents containing N atoms are advantageous in that the crosslinking reaction (e.g., reaction with a carboxy group in the base polymer) is promoted by the catalytic action of the N atom, making it easier to increase the gel fraction of the adhesive. Specific examples of crosslinking agents containing N atoms include the above-mentioned isocyanate crosslinking agents, as well as epoxy crosslinking agents containing N atoms (e.g., epoxy crosslinking agents having a glycidylamino group, such as N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-glycidylaminomethyl)cyclohexane). By appropriately setting the amount of the crosslinking agent containing N atoms to be used, it is easy to obtain an adhesive sheet that is suitable for both light peelability and surface shape conformability (preferably, furthermore, adhesive residue prevention and reduction of the step between the semiconductor chip and the encapsulating resin).

In some embodiments, the amount of crosslinking agent (preferably a crosslinking agent that forms a crosslinked structure by reacting with the carboxy groups, such as an epoxy-based crosslinking agent or an isocyanate-based crosslinking agent) used relative to the amount of carboxy groups in the base polymer (e.g., an acrylic polymer) is preferably 0.08 molar equivalents or more and 2 molar equivalents or less, more preferably 0.1 molar equivalents or more and 1 molar equivalent or less. By crosslinking the above amount of crosslinking agent with the carboxy groups in the base polymer, a pressure-sensitive adhesive sheet having fewer residual carboxy groups in the first pressure-sensitive adhesive layer can be obtained.

A crosslinking catalyst may be used to promote the crosslinking reaction more effectively. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, and dioctyltin dilaurate. The amount of the crosslinking catalyst used is not particularly limited. In some embodiments, the amount of the crosslinking catalyst used per 100 parts by weight of the base polymer can be, for example, 0.0001 parts by weight or more and 1 part by weight or less (preferably 0.001 parts by weight or more and 0.5 parts by weight or less), taking into consideration the balance between the speed of the crosslinking reaction and the length of the pot life of the adhesive composition.

(Other additives)
The first pressure-sensitive adhesive layer may contain other suitable additives as optional components, if necessary, such as tackifiers, plasticizers (e.g., trimellitic acid ester plasticizers, pyromellitic acid ester plasticizers, etc.), pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, UV absorbers, light stabilizers, release regulators, softeners, surfactants, flame retardants, antioxidants, etc.

Any suitable tackifier can be used as the tackifier. For example, a tackifier resin can be used as the tackifier. Specific examples of the tackifier resin include rosin-based tackifier resins (e.g., unmodified rosin, modified rosin, rosin phenolic resins, rosin ester resins, etc.), terpene-based tackifier resins (e.g., terpene resins, terpene phenolic resins, styrene-modified terpene resins, aromatic modified terpene resins, hydrogenated terpene resins), hydrocarbon-based tackifier resins (e.g., aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aromatic hydrocarbon resins (e.g., styrene-based resins, xylene-based resins, etc.), aliphatic/aromatic petroleum resins, aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone indene resins, etc.), phenol-based tackifier resins (e.g., alkylphenol resins, xylene formaldehyde resins, resols, novolacs, etc.), ketone-based tackifier resins, polyamide-based tackifier resins, epoxy-based tackifier resins, and elastomer-based tackifier resins. Among these, rosin-based tackifier resins, terpene-based tackifier resins, and hydrocarbon-based tackifier resins (such as styrene-based resins) are preferred. Tackifiers can be used alone or in combination of two or more.

In some embodiments, a resin with a high softening point or glass transition temperature (Tg) is used as the tackifier resin. By using a resin with a high softening point or glass transition temperature (Tg), it is possible to form an adhesive layer that can exhibit high adhesion even in a high-temperature environment (for example, a high-temperature environment during processing such as semiconductor chip encapsulation). The softening point of the tackifier is preferably 100°C to 180°C, more preferably 110°C to 180°C, and even more preferably 120°C to 180°C. The glass transition temperature (Tg) of the tackifier is preferably 100°C to 180°C, more preferably 110°C to 180°C, and even more preferably 120°C to 180°C.

In some embodiments, a low-polarity tackifier resin is used as the tackifier resin. Using a low-polarity tackifier resin is advantageous from the viewpoint of forming an adhesive layer with low affinity to the sealing material. Examples of low-polarity tackifier resins include aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aromatic hydrocarbon resins (e.g., styrene-based resins, xylene-based resins, etc.), aliphatic/aromatic petroleum resins (sometimes referred to as C5/C9 petroleum resins), aliphatic/alicyclic petroleum resins, and hydrocarbon tackifier resins such as hydrogenated hydrocarbon resins. Among these, aliphatic/aromatic petroleum resins are preferred. Such tackifier resins are low polar, have excellent compatibility with acrylic polymers, do not undergo phase separation over a wide temperature range, and can form an adhesive layer with excellent stability.

Although not particularly limited, in some embodiments, the acid value of the tackifier resin is preferably 40 or less, more preferably 20 or less, and even more preferably 10 or less. Within such a range, a pressure-sensitive adhesive layer having low affinity with the sealing material can be formed. The hydroxyl value of the tackifier resin is preferably 60 or less, more preferably 40 or less, and even more preferably 20 or less. Within such a range, a pressure-sensitive adhesive layer having low affinity with the sealing material and suitable for suppressing component migration between the pressure-sensitive adhesive layer and the sealing resin can be formed.

The amount of tackifier used may be, for example, 5 parts by weight or more and 100 parts by weight or less, and preferably 8 parts by weight or more and 50 parts by weight or less, per 100 parts by weight of the base polymer. By using an appropriate amount of tackifier, it is possible to preferably obtain a pressure-sensitive adhesive that adheres well to the adherend.

<Substrate>
The substrate of the pressure-sensitive adhesive sheet disclosed herein may be, for example, a resin sheet, a nonwoven fabric, paper, a metal foil, a woven fabric, a rubber sheet, a foam sheet, a laminate thereof (particularly, a laminate including a resin sheet), etc. Examples of the resin constituting the resin sheet include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, ethylene-vinyl acetate copolymer (EVA), polyamide (nylon), wholly aromatic polyamide (aramid), polyimide (PI), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), fluorine-based resin, polyether ether ketone (PEEK), etc. Examples of the nonwoven fabric include nonwoven fabrics made of natural fibers having heat resistance, such as nonwoven fabrics containing Manila hemp; synthetic resin nonwoven fabrics such as polypropylene resin nonwoven fabrics, polyethylene resin nonwoven fabrics, and ester resin nonwoven fabrics, etc. Examples of the metal foil include copper foil, stainless steel foil, aluminum foil, etc. Examples of the paper include Japanese paper and craft paper.

In some embodiments, a resin sheet made of a resin having a glass transition temperature (Tg) of 25°C or higher (preferably 40°C or higher, more preferably 50°C or higher) is preferably used as the substrate. By using such a resin sheet, the shape of the substrate is maintained even when heated during the sealing process, and the semiconductor chip is prevented from being embedded in the adhesive sheet. The resin constituting such a resin sheet is preferably a polymer having an aromatic ring, and specific examples include, but are not limited to, polyethylene terephthalate (PET), polyimide, polyethylene naphthalate, etc.

The thickness of the substrate can be set to any appropriate thickness depending on the desired strength or flexibility, the purpose of use, etc. The thickness of the substrate is preferably 1000 μm or less, more preferably 25 μm or more and 1000 μm or less, and may be 40 μm or more and 500 μm or less, 60 μm or more and 300 μm or less, or 80 μm or more and 250 μm or less. In one embodiment, a substrate having a thickness of 25 μm or more is used. A substrate of such a thickness is likely to maintain the shape of the substrate even when pressure is applied during the sealing process, and is suitable for preventing the semiconductor chip from being embedded in the adhesive sheet. From the viewpoint of handleability, etc., the thickness of the substrate may be 150 μm or less, 100 μm or less, or 50 μm or less.

In one embodiment, the thickness of the substrate is 20% or more and 90% or less (preferably 20% or more and 89% or less, more preferably 20% or more and 88% or less) of the total thickness of the adhesive sheet. In this range, embedding of the semiconductor chip in the adhesive sheet can be suitably prevented.

The substrate may be surface-treated. Examples of surface treatments include corona treatment, chromate treatment, ozone exposure, flame exposure, high-voltage shock exposure, ionizing radiation treatment, and coating with a primer.

As the undercoat agent, an organic coating material may be used. Examples of the organic coating material include those described in "Plastic Hard Coat Materials II" (published in 2004) by CMC Publishing. A urethane-based polymer is preferably used, and more preferably polyacrylic urethane, polyester urethane, or a precursor thereof. This is because they are easy to apply to the substrate, can be selected from a wide variety of materials industrially, and are inexpensively available. The urethane-based polymer is, for example, a polymer made of a reaction mixture of an isocyanate monomer and an alcoholic hydroxyl group-containing monomer (for example, a hydroxyl group-containing acrylic compound or a hydroxyl group-containing ester compound). The organic coating material may contain, as an optional additive, a chain extender such as polyamine, an antiaging agent, an oxidation stabilizer, and the like. The thickness of the organic coating layer is not particularly limited, but is, for example, suitable to be about 0.1 μm to 10 μm, preferably about 0.1 μm to 5 μm, and more preferably about 0.5 μm to 5 μm.

<Second Pressure-Sensitive Adhesive Layer>
The adhesive sheet disclosed herein comprises the substrate, the first adhesive layer disposed on one side of the substrate, and a second adhesive layer disposed on the substrate opposite to the first adhesive layer. An adhesive sheet (substrate-attached double-sided adhesive sheet) having such a configuration is easy to use because, for example, the second adhesive layer can be used to fix the sheet on a suitable carrier (e.g., SUS plate, glass plate, etc.) and a resin sealing step can be performed on the first adhesive layer. The second adhesive layer can be an adhesive layer composed of any suitable adhesive.

At least the surface of the second adhesive layer is composed of an adhesive containing heat-expandable microspheres. This type of adhesive sheet is preferable because it can be heated at an appropriate timing as necessary to expand the heat-expandable microspheres, thereby easily releasing the bond between the second adhesive layer and the adherend (e.g., the carrier).

The adhesive containing the heat-expandable microspheres may be a curable adhesive (e.g., an active energy ray curable adhesive) or a pressure-sensitive adhesive. Examples of pressure-sensitive adhesives include acrylic adhesives and rubber adhesives. For details of the adhesive contained in the second adhesive layer, see, for example, JP 2018-009050 A. The entire disclosure of this publication is incorporated herein by reference.

As the heat-expandable microspheres, any suitable heat-expandable microspheres can be used as long as they are microspheres that can expand or foam when heated. For example, the heat-expandable microspheres can be microspheres in which a substance that easily expands when heated is encapsulated in an elastic shell. Such heat-expandable microspheres can be produced by any suitable method, such as a coacervation method or an interfacial polymerization method.

Examples of substances that expand easily when heated include low-boiling liquids such as propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, normal hexane, isohexane, heptane, octane, petroleum ether, methane halides, and tetraalkylsilanes; azodicarbonamide, which gasifies by thermal decomposition; etc.

Examples of materials constituting the shell include polymers composed of nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, and chlorostyrene; and amide monomers such as acrylamide, substituted acrylamide, methacrylamide, and substituted methacrylamide. Polymers composed of these monomers may be homopolymers or copolymers. Examples of such copolymers include vinylidene chloride-methyl methacrylate-acrylonitrile copolymer, methyl methacrylate-acrylonitrile-methacrylonitrile copolymer, methyl methacrylate-acrylonitrile copolymer, acrylonitrile-methacrylonitrile-itaconic acid copolymer, etc.

The thermally expandable microspheres may be inorganic or organic foaming agents. Examples of inorganic foaming agents include ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and various azides. Examples of organic blowing agents include fluorinated alkane compounds such as trichloromonofluoromethane and dichloromonofluoromethane; azo compounds such as azobisisobutyronitrile, azodicarbonamide, and barium azodicarboxylate; hydrazine compounds such as paratoluenesulfonylhydrazide, diphenylsulfone-3,3'-disulfonylhydrazide, 4,4'-oxybis(benzenesulfonylhydrazide), and allylbis(sulfonylhydrazide); semicarbazide compounds such as p-toluylenesulfonylsemicarbazide and 4,4'-oxybis(benzenesulfonylsemicarbazide); triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitroso compounds such as N,N'-dinitrosopentamethylenetetramine and N,N'-dimethyl-N,N'-dinitrosoterephthalamide.

The heat-expandable microspheres may be commercially available products. Specific examples of commercially available heat-expandable microspheres include "Matsumoto Microsphere" (grades: F-30, F-30D, F-36D, F-36LV, F-50, F-50D, F-65, F-65D, FN-100SS, FN-100SSD, FN-180SS, FN-180SSD, F-190D, F-260D, F-2800D) manufactured by Matsumoto Yushi Seiyaku Co., Ltd., and "Expancel" (grades: 053- 40, 031-40, 920-40, 909-80, 930-120), Kureha Chemical Industry's "Dieform" (grades: H750, H850, H1100, S2320D, S2640D, M330, M430, M520), Sekisui Chemical's "Advancell" (grades: EML101, EMH204, EHM301, EHM302, EHM303, EM304, EHM401, EM403, EM501), etc.

The particle size of the heat-expandable microspheres before heating is preferably 0.5 μm to 80 μm, more preferably 5 μm to 45 μm, even more preferably 10 μm to 20 μm, and particularly preferably 10 μm to 15 μm. Thus, the particle size of the heat-expandable microspheres before heating, expressed in terms of average particle size, is preferably 6 μm to 45 μm, more preferably 15 μm to 35 μm. The particle size and average particle size mentioned above are values determined by a particle size distribution measurement method using a laser scattering method.

The thickness of the adhesive layer (for example, the thickness of the second adhesive layer; the same applies hereinafter unless otherwise specified) made of an adhesive containing heat-expandable microspheres is not particularly limited, and can be, for example, 3 μm or more. From the viewpoint of suppressing the decrease in smoothness of the adhesive surface due to the inclusion of heat-expandable microspheres, the thickness of the adhesive layer is usually appropriate to be 7 μm or more, preferably more than 10 μm, may be more than 15 μm, may be more than 25 μm, or may be more than 35 μm. The upper limit of the thickness of the adhesive layer is not particularly limited, but is usually appropriate to be 300 μm or less, may be 200 μm or less, may be 150 μm or less, may be 100 μm or less, or may be 70 μm or less. It may be advantageous for the thickness of the adhesive layer not to be too large in terms of avoiding the adhesive layer from cohesive failure due to the expansion of the heat-expandable microspheres. In some embodiments, the thickness of the adhesive layer may be 60 μm or less, may be 50 μm or less, or may be 45 μm or less.

The thickness Ta of the pressure-sensitive adhesive layer is preferably larger than the average particle diameter D of the heat-expandable microspheres before heating. In other words, Ta/D is preferably larger than 1.0. From the viewpoint of smoothness of the adhesive surface, in some embodiments, Ta/D is preferably 2.0 or more, may be 3.0 or more, or may be 4.0 or more. From the viewpoint of easily exerting the peeling effect due to the expansion of the heat-expandable microspheres, Ta/D is usually appropriately 50 or less, preferably 20 or less, may be 15 or less, or may be 10 or less.

The heat-expandable microspheres preferably have a suitable strength so that they do not burst until the volume expansion rate reaches 5 times or more, more preferably 7 times or more, and even more preferably 10 times or more. When using such heat-expandable microspheres, the adhesive strength can be efficiently reduced by heat treatment.

The content of heat-expandable microspheres in an adhesive containing heat-expandable microspheres can be appropriately set according to the desired degree of adhesive strength reduction, etc. The content of heat-expandable microspheres is, for example, 1 to 150 parts by weight, preferably 10 to 130 parts by weight, and more preferably 20 to 100 parts by weight, per 100 parts by weight of the base polymer of the adhesive containing heat-expandable microspheres.

When the adhesive constituting the surface of the second adhesive layer contains heat-expandable microspheres, the arithmetic mean roughness Ra of the surface of the second adhesive layer before the heat-expandable microspheres expand (i.e., before heating) is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. Within such a range, an adhesive sheet having excellent adhesion to an adherend on the second adhesive layer side can be obtained. The second adhesive layer having such excellent surface smoothness can be obtained, for example, by setting the thickness of the adhesive layer within the above range, applying an adhesive composition containing heat-expandable microspheres to a release liner and drying the adhesive layer to form an adhesive layer, and transferring the adhesive layer directly to a substrate or onto an intermediate layer (e.g., an elastic intermediate layer) provided on the substrate.

When the second adhesive layer contains heat-expandable microspheres, the adhesive layer preferably contains an adhesive composed of a base polymer whose dynamic storage modulus at 80°C is in the range of 5 kPa to 1 MPa (more preferably 10 kPa to 0.8 MPa). Such an adhesive layer can form an adhesive sheet that has appropriate adhesion before heating and whose adhesive strength is easily reduced by heating. The dynamic storage modulus can be measured using a dynamic viscoelasticity measuring device (for example, "ARES" manufactured by Rheometrics) under measurement conditions of a frequency of 1 Hz and a heating rate of 10°C/min.

<Other layers>
In some embodiments, the first adhesive layer is disposed directly on the substrate, although the adhesive sheets disclosed herein may have an intermediate layer (e.g., a non-adhesive viscoelastic layer, etc.) between the first adhesive layer and the substrate.

<Method of manufacturing pressure-sensitive adhesive sheet>
The pressure-sensitive adhesive sheet of the present invention can be produced by any suitable method. The pressure-sensitive adhesive sheet of the present invention can be produced, for example, by a method of forming a pressure-sensitive adhesive layer (which may be a first pressure-sensitive adhesive layer or a second pressure-sensitive adhesive layer) by directly applying a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive layer (which may be a first pressure-sensitive adhesive layer or a second pressure-sensitive adhesive layer) to a substrate or an intermediate layer (e.g., an elastic intermediate layer, etc.) provided on the substrate to form a pressure-sensitive adhesive layer, a method of applying a pressure-sensitive adhesive composition to any suitable peelable processing material (e.g., a release liner) to form a pressure-sensitive adhesive layer on the peelable processing material, and transferring the pressure-sensitive adhesive layer to a substrate or an intermediate layer on the substrate, or a combination thereof. The pressure-sensitive adhesive composition can be a solvent-based pressure-sensitive adhesive composition containing any suitable solvent.

When forming an adhesive layer containing heat-expandable microspheres, the adhesive layer can be formed by coating a substrate with a composition containing heat-expandable microspheres, an adhesive, and any suitable solvent. Alternatively, the adhesive layer containing heat-expandable microspheres can be formed by sprinkling heat-expandable microspheres on the adhesive coating layer and then embedding the heat-expandable microspheres in the adhesive using a laminator or the like.

Any appropriate coating method can be used for coating the above adhesive and each composition. For example, each layer can be formed by coating and then drying. Examples of the coating method include coating methods using a multi-coater, die coater, gravure coater, applicator, etc. Examples of the drying method include natural drying and heat drying. The heating temperature when heat drying is performed can be set to any appropriate temperature depending on the characteristics of the material to be dried.

Several examples of the present invention are described below, but it is not intended that the present invention be limited to these specific examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

<Evaluation method>
1. FT-IR measurement The adhesive sheet was cut into a size of about 1 cm square, and the evaluation sample was etched from the surface side of the first adhesive layer with Ar gas cluster ions, and a position 5 μm deep from the surface of the substrate side of the first adhesive layer was exposed on the surface, and then a predetermined Ge prism was pressed against it to perform microscopic FT-IR measurement. The measurement position corresponds to a position 15 μm deep from the surface of the first adhesive layer when the thickness of the first adhesive layer is 20 μm, for example, so the first adhesive layer surface was etched from the surface to a position 15 μm deep from the surface of the first adhesive layer with Ar gas cluster ions, and the exposed surface was measured. The measurement conditions for the FT-IR were as follows.
Apparatus: Nicolet 6700/Thunderdome, manufactured by Thermo Fisher Scientific
Measurement mode: ATR (single reflection) method Incident angle: 45°
Resolution: 4 ^cm
Measurement range: 4000 cm ^-1 to 675 cm ^-1
Number of integrations: 128 times Detector: MCT
Prism: Ge prism for IR microscope. The ratio of each peak intensity determined based on the peak intensity present in the range of 1725 cm ^-1 to 1750 cm ^-1 was calculated using analysis software "OMNIC ver.9" (manufactured by Thermo Fisher Scientific).
In addition, the FT-IR spectrum after the epoxy-based resin treatment on the surface of the first adhesive layer to measure the increase in peak intensity derived from the epoxy-based resin was obtained by peeling off the epoxy-based resin from an adhesive sheet that had been subjected to the epoxy-based resin treatment described below, obtaining an evaluation sample in the same manner as above, etching it with Ar gas cluster ions, and performing FT-IR measurement at a position 5 μm deep from the surface of the first adhesive layer facing the substrate.
The peak intensity in the range of 1700 cm ^-1 to 1710 cm ^-1 and the peak intensity ratio in the range of 2955 cm ^-1 to 2965 cm ^-1 are determined by FT-IR measurement of the first pressure-sensitive adhesive layer before the epoxy resin treatment.

2. Epoxy resin treatment on the surface of the first adhesive layer The adhesive sheet was cut to a size of 40 mm wide and 200 mm long, and a mold (opening size: rectangular with a width of 20 mm and a length of 180 mm, thickness: 188 μm, material: polyethylene terephthalate) was attached to the surface of the first adhesive layer. Granular epoxy resin-based sealing material (Sumitomo Bakelite Co., Ltd., G770) was sprayed into the mold so that the resin thickness after curing was 0.188 mm, and then a silicone-treated release liner was placed on top. Using a heat press machine (Tester Sangyo Co., Ltd., model number: TP-701-B HEAT SEAL TESTER), the sealing resin was heated and molded on the first adhesive layer under conditions of a temperature of 145° C., pressure conditions of 0.2 MPa (stage size of 300 mm square), and a heating and pressing time of 400 seconds. This was heated at 150° C. for 4 hours to harden the sealing resin, and then left to stand for 24 hours in an environment of 23° C. and 50% RH The epoxy resin-based sealing material is an epoxy resin containing an aromatic ring.

3. Adhesion to sealing resin The adhesive sheet after the epoxy resin treatment on the surface of the first adhesive layer was cut into a size of 10 mm wide and 88 mm long at the contact portion between the sealing resin and the first adhesive layer to prepare an evaluation sample. After leaving this evaluation sample in an environment of 100°C for 30 minutes, the load when peeling the adhesive sheet (first adhesive layer side) from the sealing resin under the conditions of a peel angle of 180 degrees and a tensile speed of 300 mm/min was measured using a tensile tester in the same environment, and the average load at that time was taken as the adhesion of the adhesive sheet (first adhesive layer) to the sealing resin. As the tensile tester, a product name "Autograph AG-120kN" manufactured by Shimadzu Corporation was used.

4. Adhesion to PET The adhesive sheet was cut to a size of 20 mm wide and 140 mm long, and the entire back side (opposite the side on which the first adhesive layer was provided) was attached to a SUS304 plate using a 2 kg hand roller via a double-sided adhesive tape (manufactured by Nitto Denko Corporation, product name "No. 531"). Note that for an adhesive sheet having a second adhesive layer on the back side of the substrate, if the second adhesive layer has a stronger adhesive strength than the first adhesive layer, instead of using the No. 531 double-sided adhesive tape, the back side of the adhesive sheet may be attached to a SUS304 plate via the second adhesive layer.
Under an environment of 23°C and 50% RH, a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., product name "Lumirror S-10", thickness 25 μm, width 30 mm) was attached as an adherend to the adhesive surface (first adhesive layer surface) of the adhesive sheet whose back side was fixed to a SUS304 plate as described above, by rolling a 2 kg roller back and forth once. After leaving this in the above environment for 30 minutes, a tensile tester was used to measure the load when the PET film was peeled from the adhesive sheet (first adhesive layer side) under conditions of a peel angle of 180 degrees and a tensile speed of 300 mm/min, and the average load at that time was taken as the adhesive strength of the adhesive sheet (first adhesive layer) to PET. As the tensile tester, a product name "Autograph AG-120kN" manufactured by Shimadzu Corporation was used.

5. Storage modulus at 23°C The storage modulus at 23°C of the first adhesive layer was measured using an apparatus named "ARES" (a viscoelasticity measuring apparatus manufactured by Rheometrics Corporation) using a film jig under measurement conditions of a heating rate of 5°C/min, a frequency of 1 Hz, and a strain of 0.1%.

6. Residual Adhesive Properties The adhesive sheet after the epoxy resin treatment on the surface of the first adhesive layer was cut into a size of 10 mm wide and 90 mm long at the contact portion between the sealing resin and the first adhesive layer to prepare an evaluation sample. The evaluation sample was heated on a hot plate heated to 190° C. for 1 minute, and then the adhesive sheet of the evaluation sample was peeled off from the sealing resin while being heated on the hot plate, and the presence or absence of adhesive residue on the sealing resin was confirmed. The peeling conditions were a pulling speed of about 1000 mm/min and a pulling angle of 120° to 180°. The presence or absence of adhesive residue was confirmed by rubbing the surface with tweezers while the sealing resin surface at the peeled-off location was heated on a hot plate, and the state thereafter was visually observed. Based on the results, if adhesive residue was observed, the adhesive residue prevention was judged to be “P” (Poor: poor adhesive residue prevention), and if no adhesive residue was observed, the adhesive residue prevention was judged to be “G” (Good: good adhesive residue prevention).

7. Standoff Evaluation A resin sealing process for a semiconductor chip (Si chip) was carried out on the surface of the first adhesive layer of the adhesive sheet under the following conditions to obtain a structure consisting of the sealing resin and the Si mirror chip.
The surface of this structure that had been in contact with the first adhesive layer surface was observed with a laser confocal microscope (OLS-5000, manufactured by OLYMPUS), and the step height (standoff height) of the interface between the Si chip and the encapsulating resin on the surface was measured for the Si chip placed at the center. If adhesive residue (glue residue) or the like was found on the surface, the residue was removed using toluene before measurement. If the standoff height was 3.5 μm or less, it was judged as "G" (Good: standoff is well suppressed), and if it was more than 3.5 μm, it was judged as "P" (Poor: standoff is insufficiently suppressed).

(conditions)
Carrier: SUS carrier (220mmΦ)
Chip: Stepped dummy chip (a dummy chip having a copper pad (pad target height 5.5 μm, mask: GNC-300 mm-G03-A-300S) on one side of a 7 mm x 7 mm x 400 μm thick silicon substrate, manufactured by Global Net Co., Ltd.)
Bonding device: Toray Engineering FC3000W
Bonding conditions: compression time 6 seconds, compression pressure 10 N, compression temperature: 23°C
Sealing equipment: Apic Yamada MS-150HP
Sealing resin: Sumitomo Bakelite G730
Preheating conditions: 130°C x 30 seconds Time from preheating to start of sealing: 1 hour Sealing temperature: 145°C
Vacuum time: 5 seconds Sealing time: 600 seconds Clamping force: 3.6 MPa
Sealing thickness: 600 μm

The sealing operation was carried out in the following manner.
1) The surface of the second adhesive layer of the double-sided adhesive sheet was attached to a SUS carrier (attaching conditions: 23° C. atmosphere, attachment cylinder pressure of 0.1 MPa, and attachment speed of 0.5 m/min).
2) Using the bonding device, a total of 25 of the stepped dummy chips were arranged on the first adhesive layer of the adhesive sheet fixed to the SUS carrier along eight radial lines with a central angle of 45 degrees, with the spacing gradually increasing from the center to the periphery. The chips were oriented so that the stepped surface (pad forming surface) of the chip faced the first adhesive layer.
3) The SUS carrier with the stepped dummy chip placed on the first adhesive layer of the adhesive sheet was preheated under specified conditions.
4) After preheating, the dummy chip was left to stand for 1 hour in an environment of 23° C. and 50% RH, and then a predetermined sealing resin was sprayed evenly over the dummy chip by hand, and the chip was sealed using predetermined sealing equipment and under predetermined sealing conditions.
5) The resulting laminate was heated at 150° C. for 4 hours to cure the sealing resin.
6) The heat-cured laminate was left to stand for 5 days in an environment of 23°C and 50% RH, and then heated on a hot plate to expand the heat-expandable microspheres in the second adhesive layer fixing the adhesive sheet to the SUS carrier, and the SUS carrier was separated from the laminate.
7) After the SUS carrier was separated, the adhesive sheet was peeled off from the laminate to obtain a structure consisting of the sealing resin and the stepped dummy chip.

Of the above evaluations, the FT-IR measurement, adhesion to sealing resin, adhesion to PET, storage modulus at 23°C, and adhesive transfer prevention were performed using a single-sided adhesive sheet with a substrate in which a first adhesive layer was placed on one side of the substrate in each of the examples described below. The stand-off evaluation was performed using a double-sided adhesive sheet (a double-sided adhesive sheet having a configuration of first adhesive layer/substrate/second adhesive layer).

<Example 1>
A first pressure-sensitive adhesive composition was prepared by adding and mixing 10 parts of a terpene phenol-based tackifier resin (manufactured by Sumitomo Bakelite Co., Ltd., product name "SUMILITE RESIN PR-12603"), 1.5 parts of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L"), and toluene for dilution to a toluene solution containing 100 parts of polymer P1 (an acrylic polymer constituted of monomer components of ethyl acrylate (EA)/2-ethylhexyl acrylate (2EHA)/methyl methacrylate (MMA)/2-hydroxyethyl acrylate (HEA) = 70/30/5/5 (weight ratio); Mw 470,000). This first adhesive composition was applied to one side of a PET film (manufactured by Toray Industries, product name "Lumirror S10", thickness 38 μm) as a substrate and dried to form a first adhesive layer (thickness 25 μm) on the substrate, thereby obtaining an adhesive sheet in which the first adhesive layer was disposed on one side of the substrate (adhesive sheet having a substrate/first adhesive layer configuration).

<Examples 2-3, 5-6>
A pressure-sensitive adhesive sheet having a substrate/first pressure-sensitive adhesive layer structure was obtained in the same manner as in Example 1, except that the thickness of the first pressure-sensitive adhesive layer was as shown in Table 1.

<Example 4>
A first pressure-sensitive adhesive composition was prepared in the same manner as in Example 2, except that a toluene solution containing polymer P2 (an acrylic polymer composed of monomer components of EA/2EHA/MMA/HEA=10/90/5/5 (weight ratio); Mw 500,000) was used instead of the toluene solution of polymer P1. A first pressure-sensitive adhesive composition was prepared using the resulting first pressure-sensitive adhesive composition to form a first pressure-sensitive adhesive layer (thickness 20 μm), thereby obtaining a pressure-sensitive adhesive sheet in which the first pressure-sensitive adhesive layer was disposed on one side of a substrate (pressure-sensitive adhesive sheet having a substrate/first pressure-sensitive adhesive layer configuration).

<Preparation of double-sided adhesive sheet>
A second adhesive composition was prepared by adding and mixing 30 parts of thermally expandable microspheres (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., product name "Matsumoto Microsphere F-190D"), 1.4 parts of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L"), 10 parts of a tackifier (manufactured by Yasuhara Chemical Co., Ltd., product name "Mighty Ace G125"), and toluene for dilution (amount totaling 100 parts) to a toluene solution containing 100 parts of polymer P3 (an acrylic polymer composed of monomer components of EA/2EHA/MMA/HEA=30/70/5/4 (weight ratio)). The obtained second adhesive composition was applied to the release-treated surface of a release film R1 (manufactured by Toray Advanced Film Co., Ltd., product name "Therapeel MDAR", thickness 38 μm) and dried to form a second adhesive layer (thickness 45 μm) on the release film R1.
The adhesive surface of the second adhesive layer formed on the release film R1 was bonded to the back surface of the substrate of each of the adhesive sheets of Examples 1 to 6, thereby obtaining a double-sided adhesive sheet having a structure of second adhesive layer/substrate/first adhesive layer.

An overview of the adhesive sheets for each example and the evaluation results are shown in Table 1.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

1: Semiconductor chip 2: Sealing resin 10: Substrate 20: First adhesive layer 30: Second adhesive layer 100, 900: Adhesive sheet

Claims (7)

A pressure-sensitive adhesive sheet comprising a substrate, a first pressure-sensitive adhesive layer disposed on one side of the substrate, and a second pressure-sensitive adhesive layer disposed on the opposite side of the substrate to the first pressure-sensitive adhesive layer,
at least a surface of the second pressure-sensitive adhesive layer is made of a pressure-sensitive adhesive containing heat-expandable microspheres;
The pressure-sensitive adhesive sheet, wherein the thickness of the first pressure-sensitive adhesive layer is 20 μm or more and 70 μm or less. The pressure-sensitive adhesive sheet according to claim 1, wherein an increase in peak intensity derived from an epoxy-based resin before and after treatment of a surface of the first pressure-sensitive adhesive layer with an epoxy-based resin is within a range of 0.000 or more and 0.030 or less, as determined based on a peak intensity in the range of 1725 cm ^-1 to 1750 ^cm -1 in an FT-IR spectrum at a measurement position located at a depth of 5 μm from the substrate side of the first pressure-sensitive adhesive layer, and wherein a peak intensity in the range of 1505 cm ^-1 to 1515 cm ^-1 is used as the peak intensity derived from the epoxy-based resin. The first pressure-sensitive adhesive layer is
the adhesion strength to an epoxy resin measured at 100° C. after treating the surface of the first pressure-sensitive adhesive layer with an epoxy resin is 0.01 N/20 mm or more and 3.00 N/10 mm or less; and
3. The pressure-sensitive adhesive sheet according to claim 1, which has an adhesive strength to a polyethylene terephthalate film measured under an environment of 23°C and 50% RH of 1.00 N/20 mm or more and 10.0 N/20 mm or less. The adhesive sheet according to claim 1 or 2, wherein the first adhesive layer has a storage modulus of 0.10 MPa or more and 0.50 MPa or less at 23°C. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the first pressure-sensitive adhesive layer has a ratio of a peak intensity in the range of 1700 cm ^-1 to 1710 cm ^-1 to a peak intensity in the range of 1725 cm ^-1 to 1750 cm ^-1 in an FT-IR spectrum of 0.325 or less. the first pressure-sensitive adhesive layer comprises an acrylic polymer;
The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the monomer component constituting the acrylic polymer contains 10 to 70% by weight of a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 6 or less carbon atoms. The pressure-sensitive adhesive sheet according to claim 1 or 2, which is used in a resin sealing process for a semiconductor chip.

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