WO2022168729A1 - Thermally conductive sheet laminate and electronic equipment using same - Google Patents

Abstract

Provided is a thermally conductive sheet laminate having low thermal resistance and excellent handling and adhesion properties.　In this thermally conductive sheet laminate 1, an adhesive film 3 is laminated onto both surfaces of a thermally conductive sheet 2. The thermally conductive sheet 2 includes: a binder resin 4 comprising a silicone resin; carbon fibers 5; and a thermally conductive filler 6 other than the carbon fibers 5. The adhesive film 2 includes a film formation component, a liquid epoxy resin, and a curing agent. The adhesive film 2 has a thickness of less than 20 μm, a viscosity at 20 °C of greater than 8.0E+05 Pa·s, and a viscosity at 130 °C of less than 40 Pa·s.

Description

Thermally conductive sheet laminate and electronic equipment using the same

This technology relates to a thermally conductive sheet laminate and an electronic device using the same. This application is Japanese Patent Application No. 2021-016137 filed on February 3, 2021 in Japan and Japanese Patent Application No. 2022-010671 filed on January 27, 2022 in Japan. Priority is claimed as a basis, and these applications are incorporated into this application by reference.

Various heat-conducting parts are being considered as heat countermeasures for semiconductor packages. For example, heat generated from various silicon dies (IC chips) is upstream of various heat sources generated from electronic equipment. Hereinafter, the thermally conductive member directly applied to the silicon die will be referred to as "TIM (Thermal Interface Material) 1". The TIM1 may be required to have the following characteristics.

The first characteristic required of TIM1 is low load mountability. Since the TIM 1 is mounted in a semiconductor packaging process, a low load (for example, about 20 psi or less) mounting condition may be desired for the purpose of protecting the shape of the microbumps of the semiconductor chip.

The second characteristic required for TIM1 is low BLT (Bond Line Thickness). From the viewpoint of the demand for a low-profile semiconductor package, it is preferable that the height of the region of the TIM1 after mounting, that is, the gap (minimum mounting gap) between the semiconductor chip and the heat spreader is as small as possible. The mounting minimum gap is sometimes desired to be, for example, 100 μm or less.

The third characteristic required of TIM1 is reliability similar to that of semiconductors. This is because TIM1, for example, is built into a semiconductor package in addition to directly acting on the silicon die interface, which is a heating element.

TIM1 that satisfies the above characteristics includes the grease type, which is a liquid product, the reactive type (adhesive type), and the solder (low-temperature solder) type, which is a solid product.

In recent years, as electronic devices have become more sophisticated, the density and mounting of semiconductor devices have increased. In addition to the conventional packaging of a single silicon die, a large chip package (SiP (System in Package)) through an interposer typified by 2.5D and 3D has been introduced. In this way, it is extremely important to efficiently dissipate heat generated from various silicon dies and semiconductor packages that constitute an electronic device in order to develop the performance of the electronic device. There is also a demand for a TIM 1 with lower thermal resistance that is compatible with next-generation packaging technology including large chip packages as described above.

A thermally conductive sheet using a carbon material can be cited as a TIM1 that is compatible with next-generation packaging technology. In particular, carbon fibers have anisotropic thermal conductivity properties. Therefore, a type of carbon fiber sheet (CFS: Carbo Fiber Sheet) in which the carbon fiber is oriented in a direction perpendicular to the surface direction of the sheet and whose shape is maintained by various binders, can withstand heat exceeding 40 W/m K. Those with conductivity have also been developed.

Against this background, what is desired is a carbon fiber sheet that satisfies the above-mentioned characteristics of TIM1 while taking advantage of the characteristics of carbon materials, for example, a carbon fiber sheet that has low thermal resistance and excellent handling and adhesiveness.

Japanese Unexamined Patent Application Publication No. 2012-201106

This technology has been proposed in view of such conventional circumstances, and provides a thermally conductive sheet laminate with low thermal resistance and excellent handleability and adhesiveness.

As a result of extensive studies by the inventors of the present invention, a thermally conductive sheet with an adhesive film (hereinafter referred to as a thermally conductive sheet laminated The inventors have found that the above problem can be solved by using the body.

In the thermally conductive sheet laminate according to the present technology, adhesive films are laminated on both sides of the thermally conductive sheet, and the thermally conductive sheet includes a binder resin made of silicone resin, carbon fiber, and heat The adhesive film contains a film-forming component, a liquid epoxy resin, and a curing agent, has a thickness of less than 20 μm, and has a viscosity at 20° C. of 8.0E+05 Pa·. s and the viscosity at 130° C. is less than 40 Pa·s.

According to this technology, it is possible to provide a thermally conductive sheet laminate with low thermal resistance and excellent handling and adhesiveness.

FIG. 1 is a cross-sectional view showing an example of a thermally conductive sheet laminate according to the present technology. FIG. 2 is a perspective view showing an example of a thermally conductive sheet in the thermally conductive sheet laminate according to the present technology. FIG. 3 is a perspective view showing an example of carbon fibers coated with an insulating coating. FIG. 4 is a cross-sectional view showing an example of a semiconductor device. FIG. 5 is a cross-sectional view schematically showing a test piece used in Examples.

In this specification, the average particle size of the thermally conductive filler is defined as the cumulative curve of the particle size value from the small particle size side of the particle size distribution when the entire particle size distribution of the thermally conductive filler is 100%. It means the particle diameter when the cumulative value is 50% when obtained. In addition, the particle size distribution (particle size distribution) in this specification is determined by volume. Examples of the method for measuring the particle size distribution include a method using a laser diffraction particle size distribution analyzer. Further, in the present specification, "ordinary temperature" refers to the range of 15 to 25°C defined in JIS K 0050:2005 (general rules for chemical analysis methods).

<Thermal conductive sheet laminate>
In the thermally conductive sheet laminate according to the present technology, adhesive films are laminated on both sides of the thermally conductive sheet. The thermally conductive sheet includes a binder resin made of silicone resin, carbon fibers, and thermally conductive fillers other than carbon fibers. The adhesive film contains a film-forming component, a liquid epoxy resin, and a curing agent. The adhesive film has a thickness of less than 20 μm, a viscosity at 20° C. of greater than 8.0E+05 Pa·s, and a viscosity at 130° C. of less than 40 Pa·s.

The adhesive film that constitutes the thermally conductive sheet laminate according to the present technology is designed so as not to hinder the thermal conductivity of the thermally conductive sheet and to improve the function of bonding the heating element and the radiator. ing. Moreover, from the viewpoint of handling, it is preferable that the adhesive film has as low tackiness as possible at around room temperature, while being excluded from between the heating element and the radiator as much as possible during the bonding process. Thus, the adhesive film preferably exhibits a low-viscosity state that is easily expelled during the heating and pressurizing process until curing starts. Therefore, the adhesive film has a viscosity at 20°C of greater than 8.0E+05 Pa·s and a viscosity at 130°C of less than 40 Pa·s.

The thermally conductive sheet laminate according to this technology has low thermal resistance and excellent handling and adhesiveness (adhesion). Therefore, after mounting, the thermally conductive sheet laminate according to the present technology can achieve high thermal conductivity due to the thermally conductive sheet and excellent adhesiveness due to the adhesive film. In addition, the thermally conductive sheet laminate has adhesive films laminated on both sides of the thermally conductive sheet. can be prevented.

FIG. 1 is a cross-sectional view showing an example of a thermally conductive sheet laminate according to the present technology. In the thermally conductive sheet laminate 1, adhesive films 3 are laminated on both sides of a thermally conductive sheet 2. As shown in FIG.

The average thickness of the thermally conductive sheet laminate 1 can be appropriately selected according to the purpose. For example, the average thickness of the thermally conductive sheet laminate 1 can be, for example, greater than 0.1 mm, and may be 0.2 mm or more. Also, the upper limit of the average thickness of the thermally conductive sheet laminate 1 can be, for example, 0.52 mm or less, and may be 0.4 mm or less. Also, the average thickness of the thermally conductive sheet laminate 1 can be in the range of 0.15 to 0.3 mm. The average thickness of the thermally conductive sheet laminate 1 can be obtained, for example, by measuring the thickness of the thermally conductive sheet laminate 1 at arbitrary five points and calculating the arithmetic mean value.

The thermal resistance of the thermally conductive sheet laminate 1 is preferably as low as possible. For example, the thermally conductive sheet laminate 1 has a thermal resistance of 0.40 cm ² ·K/W or less under a load of 1 kgf/cm ² , and may be 0.35 cm ² ·K/W or less. It may be 30 cm ² ·K/W or less, may be 0.25 cm ² ·K/W or less, may be 0.20 cm ² ·K/W or less, or may be 0.15 cm ² ·K/W or less. It may be W or less, or may be 0.10 cm ² ·K/W or less. The thermal resistance of the thermally conductive sheet laminate 1 can be measured by the method of Examples described later.

The thickness of the thermally conductive sheet 2 can be in the range of 0.1-0.5 mm. From the viewpoint of the thermal properties of the thermally conductive sheet 2, the surface roughness Ra of the thermally conductive sheet 2 can be, for example, 25 μm or less, can be 20 μm or less, and can be in the range of 20 to 25 μm. You can also The surface roughness Ra of the thermally conductive sheet 2 can be measured by the method described later in Examples.

The thickness of the adhesive film 3 may be less than 20 μm, for example, 0.1 μm or more, 1 μm or more, 3 μm or more, 7 μm or more, It may be 15 μm or more, and may be in the range of 0.1 to 15 μm. When the thickness of the adhesive film 3 is less than 20 μm, the thermal conductivity of the thermally conductive sheet 2 can be prevented from being hindered, and the thermal resistance of the thermally conductive sheet laminate 1 can be reduced. contribute.

The heat-conducting sheet 2 generally has a low surface smoothness because the hard carbon fiber 5 and the soft binder resin 4 are cut at the same time. By filling the surface with low surface smoothness (roughened surface) with the adhesive film 3 and improving the adhesion to the interface between the heating element and the radiator, the thermal resistance of the thermally conductive sheet 2 can be improved. On the other hand, the adhesive film 3 has a low thermal conductivity as a bulk, and if the area of the adhesive film 3 expands too much in the thickness direction (thermal conduction path) of the thermal conductive sheet 2, the contribution as a thermal resistance component increases. Therefore, the thickness of the adhesive film 3 is preferably such that the surface roughness Ra of the heat conductive sheet 2 is filled. The thickness of the adhesive film 3 can be selected according to the surface roughness Ra of the heat conductive sheet 2. If the two surfaces of the heat conductive sheet 2 have different surface roughnesses Ra, the thickness of the adhesive film 3 is reduced by heating. It is sufficient to correspond to the surface roughness Ra of the conductive sheet 2 . For example, the ratio of the thickness (μm) of the adhesive film 3 to the surface roughness Ra (μm) of the thermally conductive sheet 2 (thickness of the adhesive film 3/surface roughness Ra of the thermally conductive sheet 2) is 0.5. 003 to 0.7, more preferably 0.05 to 0.3. Even if the adhesive film 3 does not have a thickness that completely fills the surface roughness Ra of the thermally conductive sheet 2, the contact heat resistance can be improved by maintaining a close contact state due to the adhesive force.

When the thermally conductive sheet laminate 1, that is, the thermally conductive sheet 2 with the adhesive film 3 cannot be adhered to the adherend at an appropriate position or cannot be adhered uniformly, a rework operation is performed. Sometimes. Examples of failures in uniformly attaching the thermally conductive sheet laminate 1 include adhesion between the adhesive films 3 and inclusion of voids at the adherend interface. If the viscosity of the adhesive film 3 is low near room temperature, the adhesive strength between the adhesive film 3 and the adherend becomes too high, and during rework, the adhesive film 3 and the adherend are not easily released from each other, and the adhesive film 3 and the heat conductive sheet 2, cohesive failure of the adhesive film 3, material breakage of the heat conductive sheet 2, etc., and the handleability of the heat conductive sheet laminate 1 tends to deteriorate. . Therefore, the viscosity of the adhesive film 3 at 20° C. is greater than 8.0E+05 Pa·s, may be 9.0E+05 Pa·s or more, may be 1.0E+06 Pa·s or more, and may range from 9.0E+05 to 1.0E+05 Pa·s. It may be in the range of 0E+06 Pa·s.

The viscosity of the adhesive film 3 at 130° C. is less than 40 Pa·s, may be 30 Pa·s or less, may be 25 Pa·s or less, may be 20 Pa·s or less, or may be 15 Pa·s. It may be less than or equal to 10 Pa·s or less, or may be in the range of 10 to 30 Pa·s. When the viscosity of the adhesive film 3 at 130° C. is less than 40 Pa·s, the adhesive film 3 is easily expelled from between the heating element and the radiator in the bonding process. The viscosity of the adhesive film 3 can be measured by the method described later in Examples.

The thermal conductivity in the thickness direction of the thermally conductive sheet laminate 1 can be, for example, 1 W/m·K or more, 4 W/m·K or more, or 7 W/m·K or more at room temperature. It can also be set to 9 W/m·K or more.

Next, configuration examples of the thermally conductive sheet 2 and the adhesive film 3 will be described.

<Heat conductive sheet>
FIG. 2 is a perspective view showing an example of the thermally conductive sheet 2 in the thermally conductive sheet laminate 1 according to the present technology. As shown in FIG. 2, the thermally conductive sheet 2 includes a binder resin 4 made of a silicone resin, carbon fibers 5, and a thermally conductive filler 6 other than the carbon fibers 5. The carbon fibers 5 and a thermally conductive A filler 6 is dispersed in the binder resin 4 . In the thermally conductive sheet 2 , long axes of carbon fibers 5 having anisotropic thermally conductive properties are oriented in the thickness direction B of the thermally conductive sheet 2 . Thus, in the thermally conductive sheet 2 in the thermally conductive sheet laminate 1, since the long axis of the carbon fibers 5 is oriented in the thickness direction B, heat conduction in the thickness direction of the thermally conductive sheet laminate 1 is achieved. It has good properties.

[Binder resin]
The binder resin 4 is for holding the carbon fibers 5 and the thermally conductive filler 6 within the thermally conductive sheet 2 . As the binder resin 4, for example, a silicone resin is used in consideration of the adhesion between the heat generating surface of the electronic component and the heat sink surface. The binder resin 4 may be used individually by 1 type, and may be used in combination of 2 or more types.

As the silicone resin, for example, a two-component addition reaction type silicone resin composed of a silicone having an alkenyl group as a main component, a main agent containing a curing catalyst, and a curing agent having a hydrosilyl group (Si—H group). can be used. As the alkenyl group-containing silicone, for example, a vinyl group-containing polyorganosiloxane can be used. The curing catalyst is a catalyst for promoting the addition reaction between the alkenyl group in the alkenyl group-containing silicone and the hydrosilyl group in the hydrosilyl group-containing curing agent. As the curing catalyst, well-known catalysts used for hydrosilylation reaction can be used. For example, platinum group curing catalysts, such as platinum group metals such as platinum, rhodium and palladium, and platinum chloride can be used. As the curing agent having hydrosilyl groups, for example, polyorganosiloxane having hydrosilyl groups can be used.

The content of the binder resin 4 in the thermally conductive sheet 2 is not particularly limited, and can be appropriately selected according to the purpose. For example, the content of the binder resin 4 in the thermally conductive sheet 2 may be 20% by volume or more, may be 25% by volume or more, or may be 30% by volume or more. The upper limit of the content of the binder resin 4 in the thermally conductive sheet 2 may be 70% by volume or less, may be 60% by volume or less, or may be 50% by volume or less. It may be 40% by volume or less. From the viewpoint of improving the flexibility of the thermally conductive sheet 2, the content of the binder resin 4 in the thermally conductive sheet 2 can be in the range of 25 to 60% by volume.

The carbon fiber 5 is, for example, a pitch-based carbon fiber, a PAN-based carbon fiber, a carbon fiber obtained by graphitizing PBO fiber, an arc discharge method, a laser evaporation method, a CVD method (chemical vapor deposition method), a CCVD method (catalytic chemical vapor deposition method). A carbon fiber synthesized by a phase growth method) or the like can be used. Among these, pitch-based carbon fibers are preferable from the viewpoint of thermal conductivity.

The average fiber length (average major axis length) of the carbon fibers 5 can be appropriately selected according to the purpose, and can be, for example, 50 to 250 μm, may be 75 to 200 μm, or can be 90 to 170 μm. may be The average fiber diameter (average minor axis length) of the carbon fibers 5 can also be appropriately selected according to the purpose, and can be, for example, 4 to 20 μm, and may be 5 to 14 μm. The aspect ratio (average major axis length/average minor axis length) of the carbon fibers 5 can be appropriately selected according to the purpose, and can be, for example, 9-30. The average major axis length and average minor axis length of the carbon fibers 5 can be measured with a microscope or scanning electron microscope (SEM), for example.

FIG. 3 is a perspective view showing an example of carbon fibers coated with an insulating coating. From the viewpoint of enhancing the insulating properties of the thermally conductive sheet 2, the surfaces of the carbon fibers 5 may be covered with an insulating coating 7, as shown in FIG. Thus, the insulation-coated carbon fiber 8 can be used as the carbon fiber. The insulation-coated carbon fiber 8 has the carbon fiber 5 and the insulation coating 7 on at least part of the surface of the carbon fiber 5, and may contain other components as necessary.

The insulating film 7 is made of an electrically insulating material, such as silicon oxide or a cured polymer material. The polymerizable material is, for example, a radical polymerizable material such as a polymerizable organic compound and a polymerizable resin. The radically polymerizable material can be appropriately selected according to the purpose as long as it is a material that undergoes radical polymerization using energy. Examples thereof include compounds having a radically polymerizable double bond. Examples of radically polymerizable double bonds include vinyl groups, acryloyl groups, and methacryloyl groups. The number of radically polymerizable double bonds in the compound having radically polymerizable double bonds is preferably two or more from the viewpoint of strength including heat resistance and solvent resistance. Examples of compounds having two or more radically polymerizable double bonds include divinylbenzene (DVB) and compounds having two or more (meth)acryloyl groups. The radically polymerizable material may be used singly or in combination of two or more. The molecular weight of the radically polymerizable material can be appropriately selected depending on the purpose, and can be in the range of 50-500, for example. When the insulating coating 5 is formed of a cured product of a polymerizable material, the content of structural units derived from the polymerizable material in the insulating coating 7 can be, for example, 50% by weight or more, and can be 90% by weight or more. can also be

The average thickness of the insulating film 7 can be appropriately selected according to the purpose, and from the viewpoint of realizing high insulation, it can be 50 nm or more, and may be 100 nm or more, or 200 nm or more. good. The upper limit of the average thickness of the insulating coating 7 can be, for example, 1000 nm or less, and may be 500 nm or less. The average thickness of the insulating coating 7 can be obtained by observation with a transmission electron microscope (TEM), for example.

Methods for coating the carbon fibers 5 with the insulating coating 7 include, for example, a sol-gel method, a liquid phase deposition method, a polysiloxane method, and polymerization of at least a portion of the surface of the carbon fibers 5 described in JP-A-2018-98515. a method of forming the insulating film 7 made of a cured material of a flexible material, and the like.

The thermally conductive filler 6 is a thermally conductive filler other than the carbon fibers 5. Examples of the material of the thermally conductive filler 6 include nitrogen compounds, metal hydroxides, and metal oxides. Nitrogen compounds include aluminum nitride and boron nitride. Metal hydroxides include aluminum hydroxide. Examples of metal oxides include aluminum oxide (alumina, sapphire), magnesium oxide, and the like. The thermally conductive fillers 6 may be used singly or in combination of two or more. The shape of the thermally conductive filler 6 is not particularly limited, and examples thereof include spherical, powdery, granular, flattened, scaly, and fibrous.

In particular, as the thermally conductive filler 6, it is preferable to use both aluminum nitride particles and alumina particles from the viewpoint of thermal conductivity. The average particle size of the aluminum nitride particles is, for example, preferably in the range of 1 to 5 μm, may be in the range of 1 to 3 μm, or may be in the range of 1 to 2 μm. Further, the average particle diameter of the alumina particles is, for example, preferably in the range of 1 to 10 μm, may be in the range of 1 to 8 μm, and may be in the range of 4 to 6 μm.

The total amount of the carbon fibers 5 and the thermally conductive fillers 6 in the thermally conductive sheet 2 is preferably as large as possible from the viewpoint of improving thermal conductivity. good too. The upper limit of the total amount of the carbon fibers 5 and the thermally conductive fillers 6 in the thermally conductive sheet 2 can be, for example, 90% by volume or less from the viewpoint of flexibility of the sheet.

The thermally conductive sheet 2 may contain more carbon fibers 5 than the thermally conductive fillers 6, may contain more thermally conductive fillers 6 than the carbon fibers 5, or may contain more carbon fibers 5 than the thermally conductive fillers 6. The same amount of filler 6 may be included.

The content of the carbon fibers 5 in the thermally conductive sheet 2 may be, for example, 5% by volume or more, may be 10% by volume or more, may be 15% by volume or more, or may be 20% by volume or more. It may be vol % or more, 22 vol % or more, or may be in the range of 10 to 25 vol %.

The content of the thermally conductive filler 6 in the thermally conductive sheet 2 may be, for example, 5% by volume or more, may be 10% by volume or more, or may be 15% by volume or more. , 20% by volume or more, 25% by volume or more, 30% by volume or more, 35% by volume or more, or 40% by volume or more may be present, may be 43% by volume or more, or may be in the range of 20 to 50% by volume. When aluminum nitride particles and alumina particles are used together as the thermally conductive filler 6, the content of the alumina particles in the thermally conductive sheet 1 is preferably 10 to 25% by volume, and the content of the aluminum nitride particles is is preferably 10 to 25% by volume.

The thermally conductive sheet 2 may further contain other components than those mentioned above. Other components include, for example, silane coupling agents, dispersants, curing accelerators, retarders, tackifiers, plasticizers, flame retardants, antioxidants, stabilizers, colorants and the like. For example, the thermally conductive sheet 2 is treated with a silane coupling agent from the viewpoint of further improving the dispersibility of the carbon fibers 5 and the thermally conductive filler 6 and further improving the flexibility of the thermally conductive sheet 2 . A conductive filler 6 may be used.

Next, a method for manufacturing the thermally conductive sheet 2 will be described. The thermally conductive sheet 2 is obtained by a manufacturing method including steps A, B, and C below.

<Step A>
In step A, a resin composition for forming a thermally conductive sheet is prepared by dispersing carbon fibers 5 and thermally conductive fillers 6 in a binder resin 4 . The resin composition for forming the thermally conductive sheet contains the carbon fibers 5, the thermally conductive filler 6, the binder resin 4, and, if necessary, various additives and volatile solvents. It can be prepared by mixing to

<Process B>
In step B, a molded block is formed from the prepared resin composition for forming a thermally conductive sheet. Examples of methods for forming the molded block include an extrusion molding method and a mold molding method. The extrusion molding method and the mold molding method are not particularly limited, and various known extrusion molding methods and mold molding methods are selected according to the viscosity of the resin composition for forming the thermally conductive sheet and the thermally conductive sheet. It can be appropriately adopted according to the characteristics to be used.

For example, when extruding a resin composition for forming a thermally conductive sheet from a die in an extrusion molding method, or when pressing a resin composition for forming a thermally conductive sheet into a mold in a mold molding method, a binder resin flows, and the carbon fibers 5 are oriented along the flow direction.

The size and shape of the molded block can be determined according to the required size of the heat conductive sheet 2. For example, a rectangular parallelepiped having a cross-sectional length of 0.5 to 15 cm and a width of 0.5 to 15 cm can be used. The length of the rectangular parallelepiped may be determined as required.

<Process C>
In step C, the molded block is sliced into sheets to obtain thermally conductive sheets 2 in which the long axes of carbon fibers 5 are oriented in the thickness direction B. As shown in FIG. The carbon fibers 5 are exposed on the surface (slice surface) of the sheet obtained by slicing. The slicing method is not particularly limited, and can be appropriately selected from among known slicing devices according to the size and mechanical strength of the compact block. When the molding method is extrusion molding, the slicing direction of the molded block is preferably 60 to 120 degrees with respect to the extrusion direction because some carbon fibers 5 are oriented in the extrusion direction. A 70-100 degree orientation is more preferred, and a 90 degree (perpendicular) orientation is even more preferred.

Thus, in the manufacturing method including Step A, Step B, and Step C, the binder resin 4, the carbon fiber 5, and the thermally conductive filler 6 are contained, and the carbon fiber 5 and the thermally conductive filler 6 are is dispersed in the binder resin 4, and the thermally conductive sheet 2 in which the major axes of the carbon fibers 5 are selectively oriented in the thickness direction B can be obtained.

The method for manufacturing the thermally conductive sheet 2 is not limited to the above example, and for example, after the process C, the process D for pressing the sliced surface may be further included. By including Step D of pressing in the method for producing a thermally conductive sheet, the surface of the sheet obtained in Step C is made smoother, and adhesion to other members can be further improved. As a method of pressing, a pair of pressing devices comprising a flat plate and a press head having a flat surface can be used. Moreover, you may press with a pinch roll. The pressure for pressing can be, for example, 0.1 to 100 MPa. In order to further enhance the effect of pressing and shorten the pressing time, it is preferable to perform pressing at a temperature higher than the glass transition temperature (Tg) of the binder resin 4 . For example, the pressing temperature can be from 0 to 180.degree. C., can be within the temperature range of room temperature (eg, 25.degree. C.) to 100.degree.

<Adhesive film>
The adhesive film 3 contains a film-forming component, a liquid epoxy resin, and a curing agent, as described above.

[Film-forming component]
The adhesive film 3 contains a film-forming component (binder component) that functions as a film-forming resin. From the viewpoint of the film formability of the adhesive film 3, the weight-average molecular weight of the film-forming component may be, for example, 200,000 or more, may be 220,000 or more, or may be 300,000 or more. Well, it may be 350,000 or more, or it may be 400,000 or more. In addition, the upper limit of the weight average molecular weight of the film-forming component can be, for example, 1,000,000 or less, may be 900,000 or less, or 800,000, from the viewpoint of the viscosity of the adhesive film 3. It may be less than or equal to 700,000 or less, or it may be less than or equal to 600,000.

The glass transition temperature of the film-forming component can be, for example, less than 30° C., may be 10° C. or less, or −10° C. or less, from the viewpoint of the reaction characteristics (for example, melt viscosity) of the adhesive film 3. may Although the lower limit of the glass transition temperature of the film-forming component is not particularly limited, it can be -30°C or higher, for example. As a method for measuring the glass transition temperature of the film-forming component, a known method can be used. For example, it can be measured using a thermomechanical analyzer at a temperature elevation rate of 10° C./min.

For example, an acrylic polymer (acrylic rubber) can be used as the film-forming component. For example, acrylic polymers having at least one selected from carboxyl groups, hydroxyl groups, epoxy groups and amide groups as functional groups can be used. A copolymer of ethyl acrylate (EA), acrylonitrile (AN), glycidyl methacrylate (GMA), and dimethylacrylamide (DMAA) can be used as the acrylic polymer. Specific examples of the film-forming component include Teisan resin series, SG-80H (Tg; 12° C.), SG-P3 (Tg; 12° C.) manufactured by Nagasemtex Co., Ltd., and the like. The film-forming component may be used singly or in combination of two or more.

The content of the film-forming component in the adhesive film 3 may be, for example, 1 part by weight or more, may be 3 parts by weight or more, or may be 5 parts by weight or more with respect to 100 parts by weight of the epoxy resin. It may be 8 parts by weight or more. Further, the upper limit of the content of the film-forming component in the adhesive film 3 can be, for example, 15 parts by weight or less with respect to 100 parts by weight of the epoxy resin, and may be 13 parts by weight or less, or 10 parts by weight. It may be less than part.

[Epoxy resin]
The epoxy resin used for the adhesive film 3 is a liquid epoxy resin at room temperature. The epoxy resin may be a monofunctional epoxy resin, a bifunctional epoxy resin, or a polyfunctional epoxy resin. Resins are preferred.

The viscosity of the epoxy resin can be, for example, 25000 mPa·s or less at room temperature, and may be 20000 mPa·s or less. The lower limit of the viscosity of the epoxy resin can be, for example, 150 mPa·s or more, and may be 200 mPa·s or more.

The epoxy equivalent of the epoxy resin can be, for example, in the range of 100-300 g/eq, and may be in the range of 100-200 g/eq.

As the epoxy resin, a polyfunctional aliphatic epoxy resin or a polyfunctional aromatic epoxy resin can be used. A specific example of the epoxy resin is BATG (an epoxidation reaction product of 2,2'-diallylbisphenol A diallyl ether with hydrogen peroxide) manufactured by Showa Denko. An epoxy resin may be used individually by 1 type, and may use 2 or more types together.

The content of the epoxy resin in the adhesive film 3 can be, for example, in the range of 10 to 65% by weight, can be in the range of 20 to 60% by weight, and can be in the range of 30 to 55% by weight. can also

[Curing agent]
The adhesive film 3 contains a curing agent. The curing agent is the curing agent for epoxy resins described above. Amine-based, phosphorus-based, phenol-based, or a combination thereof can be used as the curing agent. As the curing agent, it is preferable to use a latent curing agent from the viewpoint of more effectively exhibiting the above-described viscosity characteristics of the adhesive film 3 . The curing agent may be used singly or in combination of two or more. For example, it is preferable to use an amine-based curing agent and a phenol-based curing agent together.

Amine curing agents include imidazoles such as 1-cyanoethyl-2-phenylimidazole, 2,4-diamino-6-(2′-methylimidazolyl-(1′))-ethyl-s-triazine, 2 -phenyl-4-methyl-5-hydroxymethylimidazole, 1-cyanoethyl-2-phenylimidazole in which position 1 of imidazole is protected with a cyanoethyl group, and 2-phenyl-4,5-dihydroxymethylimidazole. A specific example of the amine-based curing agent is Fujicure 7004 manufactured by T&K TOKA.

When the adhesive film 3 contains an amine-based curing agent as a curing agent, the content of the amine-based curing agent in the adhesive film 3 may be 0.1 parts by weight or more with respect to 100 parts by weight of the epoxy resin. It may be 0.2 parts by weight or more, may be 0.5 parts by weight or more, may be 1 part by weight or more, may be 1.5 parts by weight or more, or may be 2 parts by weight. It may be more than part. The upper limit of the content of the amine-based curing agent in the adhesive film 3 may be, for example, 5 parts by weight or less, may be 3 parts by weight or less, or may be 2.5 parts by weight or less. It may be 2.0 parts by weight or less.

Phenolic curing agents include phenol novolac compounds, cresol novolak compounds, aromatic hydrocarbon formaldehyde resin-modified phenol compounds, dicyclopentadiene phenol addition type compounds, and phenol aralkyl compounds. A specific example of the phenolic curing agent is TD-2131 manufactured by DIC.

When the adhesive film 3 contains a phenolic curing agent as a curing agent, the content of the phenolic curing agent is determined according to the epoxy equivalent of the epoxy resin. The content of the phenol-based curing agent in the adhesive film 3 is preferably 65 parts by weight or more, more preferably 70 parts by weight or more, with respect to 100 parts by weight of the epoxy resin having an epoxy equivalent of 120. The upper limit of the content of the phenol-based curing agent in the adhesive film 3 is preferably 90 parts by weight or less, more preferably 85 parts by weight or less, more preferably 80 parts by weight with respect to 100 parts by weight of the epoxy resin having an epoxy equivalent of 120. It is also possible to make it less than a part. The content of the phenol-based curing agent in the adhesive film 3 may be in the range of 65 to 90 parts by weight, or in the range of 70 to 85 parts by weight, with respect to 100 parts by weight of the epoxy resin having an epoxy equivalent of 120. can also

[Filler]
The adhesive film 3 may further contain a filler, for example, for the purpose of adjusting the fluidity of the adhesive film 3 during pressure bonding. In addition, since the adhesive film 3 contains a filler, the strength of the adhesive film 3 can be further improved, and the material breakage of the adhesive film 3 can be prevented more effectively during rework work, especially when the adhesive films 3 are adhered to each other. can. Examples of fillers that can be used include inorganic fillers such as silica, talc, titanium oxide, calcium carbonate, and magnesium oxide, with silica being preferred. A specific example of the filler is SO-C1 manufactured by Admatechs. A filler may be used individually by 1 type, and may use 2 or more types together. The total content of the filler in the adhesive film 3 can be, for example, 26 to 50 parts by weight, and can also be 26 to 45 parts by weight, with respect to 100 parts by weight of the epoxy resin.

Next, a method for manufacturing the adhesive film 3 will be described. First, a mixed solution is prepared by dissolving the adhesive film composition containing the above-described film-forming component, liquid epoxy resin, and curing agent in a solvent. As the solvent, toluene, ethyl acetate, etc., or a mixed solvent thereof can be used. After the mixed solution is prepared, it is applied onto a release substrate using a bar coater, a coating device, or the like. The release base material has a laminate structure in which a release agent such as silicone is applied to PET (Poly Ethylene Terephthalate), OPP (Oriented Polypropylene), PMP (Poly-4-methylpentene-1), PTFE (Polytetrafluoroethylene), or the like. , to prevent the mixed liquid from drying and to maintain the shape of the mixed liquid. Then, the mixed solution applied on the release base material is dried using a heat oven, a heat drying device, or the like. Thereby, an adhesive film 3 having a predetermined thickness is obtained.

<Method for producing thermally conductive sheet laminate>
The thermally conductive sheet laminate 1 is, for example, placed on both sides of the thermally conductive sheet 2 while the adhesive film 3 is heated on a heated stage, and the thermally conductive sheet 2 and the adhesive film are pressed under a predetermined pressure. 3 can be produced by bonding together.

<Electronic equipment>
The thermally conductive sheet laminate 1 is, for example, an electronic device ( heat dissipation structure). An electronic device to which the thermally conductive sheet laminate 1 is applied includes a heating element, a radiator, and the thermally conductive sheet laminate 1 disposed between the heating element and the radiator. are bonded with the thermally conductive sheet laminate 1 . As described above, in the electronic device to which the thermally conductive sheet laminate 1 is applied, the heating element and the radiator are adhered via the adhesive film 3 of the thermally conductive sheet laminate 1, so the thermally conductive sheet 2 The adhesive film 3 provides good adhesion while achieving high thermal conductivity.

The heating element is not particularly limited. and electronic components that generate heat in. The heating element also includes components for receiving optical signals, such as optical transceivers in communication equipment.

The radiator is not particularly limited, and examples include those used in combination with integrated circuit elements, transistors, optical transceiver housings, such as heat sinks and heat spreaders. As the radiator, in addition to the heat spreader and the heat sink, any material can be used as long as it conducts the heat generated from the heat source and dissipates it to the outside. A heat pipe, a metal cover, a housing, and the like can be mentioned.

An electronic device has at least a heating element, a radiator, and a thermally conductive sheet laminate 1, and may further have other members as necessary.

FIG. 4 is a cross-sectional view showing an example of a semiconductor device 50 to which the thermally conductive sheet laminate 1 according to the present technology is applied. As shown in FIG. 4, the thermally conductive sheet laminate 1 is mounted on a semiconductor device 50 incorporated in various electronic devices, and sandwiched between a heat generator and a radiator. A semiconductor device 50 shown in FIG. 4 includes an electronic component 51 , a heat spreader 52 , and a thermally conductive sheet laminate 1 . . By sandwiching the thermally conductive sheet laminate 1 between the heat spreader 52 and the heat sink 53 , together with the heat spreader 52 , a heat dissipation member for dissipating heat from the electronic component 51 is formed. The mounting location of the thermally conductive sheet laminate 1 is not limited to between the heat spreader 52 and the electronic component 51, but may be between the heat spreader 52 and the heat sink 53, or may be depending on the configuration of the electronic device or semiconductor device. can be selected as appropriate.

An example of this technology will be described below. Note that the present technology is not limited to these examples.

<Preparation of thermally conductive sheet>
23% by volume of aluminum nitride particles with an average particle size of 1 μm and 20% by volume of alumina particles with an average particle size of 5 μm, which are coupled with a silane coupling agent, in a two-liquid addition reaction type liquid silicone, and an average of fibrous fillers 22% by volume of pitch-based carbon fibers having a fiber length of 150 μm were mixed to prepare a silicone composition. The two-liquid addition reaction type liquid silicone resin is mainly composed of organopolysiloxane, and the mixing ratio of the silicone agent A and agent B is 17.5 vol%:17.5 vol%. compounded. The resulting silicone composition is extruded into a hollow square prism-shaped mold (50 mm x 50 mm) with a release-treated film pasted along the inner wall to form a 50 mm square silicone molded body, which is then placed in an oven. was heated at 100° C. for 6 hours to obtain a silicone cured product. After the cured silicone product was removed from the hollow square prism-shaped mold, the release-treated film was peeled off and cut with a slicer to a thickness of 0.5 mm. The surface roughness Ra of the cut surface of the cured silicone product (thermally conductive sheet) was 25 μm. The surface roughness Ra of the cut surface of the silicone cured product (thermally conductive sheet) was measured using a three-dimensional profiler (manufactured by ZYGO).

<Production of adhesive film>
The following components were used for the adhesive film.
Acrylic polymer A (monomer composition: EA-AN-GMA-DMAA, Mw 350,000)
Acrylic polymer B (monomer composition: EA-AN-GMA-DMAA, Mw 220,000)
BATG: Tetrafunctional epoxy resin (manufactured by Showa Denko), viscosity 15,000 mPa s, epoxy equivalent 120 g/eq
TD-2131: phenolic curing agent (manufactured by DIC, hydroxyl equivalent 104 g/eq)
Fujicure 7004: latent curing agent (manufactured by T&K TOKA)
SO-C1: Filler (manufactured by Admatechs)

Each component was weighed so that the blending amount (parts by weight) shown in Table 1 was obtained, and the mixed solution mixed with a solvent was applied on a PET film whose surface had been subjected to mold release treatment in advance, and then formed into a film. , the solvent was volatilized to prepare an adhesive film.

<Thermal conductive sheet laminate>
While the adhesive film is heated on a stage heated to 80° C., it is placed on both sides of the thermally conductive sheet, and the thermally conductive sheet and the adhesive film are bonded together at a pressure of 10 kPa for 10 seconds. 1, a thermally conductive sheet laminate 1 in which adhesive films 3 are laminated on both sides of a thermally conductive sheet 2 was produced.

<Preparation of test piece>
FIG. 5 is a cross-sectional view schematically showing a test piece used in Examples. The thermally conductive sheet laminate 1 is placed on a bare silicon die 62 (size: 20 mm×20 mm, thickness 750 μm) that is adhered to a PCB 61 (size: 50 mm×50 mm). , Ni-plated Cu (thickness 1.0 mm) material IHS (Integrated heat spreader) 64 (size: 40 mm × 40 mm) is attached, and heated and pressed at 150 ° C. and 10 kPa for 1 hour, as shown in FIG. A test piece 60 having a package structure was prepared.

<Thermal resistance>
Using a thermal resistance measuring device conforming to ASTM-D5470, the thermal resistance value (cm ² ·K/W) of the thermally conductive sheet laminate 1 was measured with a load of 1 kgf/cm ² applied. Table 1 shows the results.

<Handleability>
The handleability of the thermally conductive sheet laminate 1 was evaluated at room temperature (25° C.) by releasability from a carrier (hand) during pick-and-place. Specifically, when there is no tackiness of the adhesive film 3 (good releasability), it is evaluated as A, and when there is tackiness of the adhesive film 3 (slightly good releasability), it is evaluated as B. C when there is tack (when any of mold release failure, peeling occurs between the adhesive film 3 and the heat conductive sheet 2, cohesive failure of the adhesive film 3, or material breakage of the heat conductive sheet 2) evaluated. Practically, it is preferable that the evaluation result of handling property is A or B, and A is more preferable. Table 1 shows the results.

<Reworkability>
Regarding the reworkability of the thermally conductive sheet laminate 1, it is possible to reposition the thermally conductive sheet laminate 1 immediately after mounting the thermally conductive sheet laminate 1 on the bare silicon die 62 at room temperature (25°C). When the thermal conductive sheet laminate 1 could not be repositioned, it was evaluated as × (NG). Table 1 shows the results.

<Initial Mounting Adhesion>
The adhesiveness of the thermally conductive sheet laminate 1 at the initial stage of mounting was observed using an ultrasonic imaging device (SAT: Scanning Acoustic Tomograph). When the thermally conductive sheet laminate 1 was partially adhered (when there was a non-bonded portion of the thermally conductive sheet laminate 1), it was evaluated as × (NG). evaluated. In the SAT, glued areas are generally displayed in gray and non-glued areas in white. Table 1 shows the results.

<Reflow resistance (adhesion reliability)>
The test piece 60 was subjected to moisture absorption for 24 hours under conditions of a temperature of 85° C. and a relative humidity of 85%, and then heated in a reflow oven at a maximum temperature of 260° C. for 3 cycles (hygroscopic reflow). The presence or absence of delamination between the bare silicon die 62 and the IHS 64 in the test piece 60 after moisture absorption reflow was observed with an ultrasonic imaging device (SAT). Before and after moisture absorption reflow, when there was no change due to peeling, it was evaluated as ◯ (OK), and when there was a change (when there was peeling after moisture absorption reflow), it was evaluated as × (NG). Table 1 shows the results.

<Reflow resistance (thermal resistance reliability)>
The test piece 60 was subjected to moisture absorption for 24 hours under conditions of a temperature of 85° C. and a relative humidity of 85%, and then heated in a reflow oven at a maximum temperature of 260° C. for 3 cycles (hygroscopic reflow). Thermal resistance (cm ² K/W) was measured by applying a load of 1 kgf/cm ² to the thermally conductive sheet laminate 1 in the test piece 60 after moisture absorption reflow using a thermal resistance measuring device conforming to ASTM-D5470. It was measured. When the thermal resistance value increase was within 10% before and after moisture absorption reflow, it was evaluated as ◯ (OK), and when the thermal resistance value increase was more than 10% before and after moisture absorption reflow, it was evaluated as × (NG). Table 1 shows the results.

<Temperature cycle (TCT) test>
The test piece 60 was subjected to a temperature cycle test of -55°C (30 min) ⇔ 125°C (30 min) for 1000 cycles. After the temperature cycle test, the test piece 60 was observed with an ultrasonic imaging device (SAT) for the presence or absence of positional changes in the constituent members of the test piece 60 . Specifically, the test piece 60 was arranged so that the direction of the arrow in FIG. It was confirmed whether or not there was a change in the position of the adhesive sheet laminate 1 with respect to each adhesive interface. Before and after the temperature cycle test, when there was no positional change in the constituent members of the test piece 60, it was evaluated as ◯ (OK), and when there was a positional change, it was evaluated as x (NG). Table 1 shows the results.

In Comparative Example 1, no adhesive film was laminated on both sides of the thermally conductive sheet, that is, the thermally conductive sheet was used. I found out not.

In Comparative Example 2, the thickness of the adhesive film was 20 μm or more, so it was found that the thermal resistance was high.

In Comparative Example 3, the viscosity of the adhesive film was 8.0E+05 Pa·s or less at 20°C, so it was found that the handleability was not good.

In Comparative Example 4, the viscosity of the adhesive film was 40 Pa·s or more at 130°C, so it was found that the thermal resistance was high.

In Comparative Example 5, the viscosity of the adhesive film was 8.0E+05 Pa·s or less at 20°C, so it was found that the reworkability and reflow resistance were not good.

On the other hand, in the thermally conductive sheet laminates used in the examples, the thickness of the adhesive film is less than 20 μm, the viscosity of the adhesive film is greater than 8.0E+05 Pa s at 20° C., and less than 40 Pa s at 130° C. Therefore, it was found that the heat resistance could be reduced, the handling property and reworkability were good, and the adhesiveness was also excellent.

1 Thermally conductive sheet laminate, 2 Thermally conductive sheet, 3 Adhesive film, 4 Binder resin, 5 Carbon fiber, 6 Thermally conductive filler, 7 Insulating coating, 8 Insulating coated carbon fiber, 50 Semiconductor device, 51 Electronic component, 52 heat spreader, 53 heat sink, 60 test piece, 61 PCB, 62 bare silicon die, 64 IHS

Claims (8)

1. A thermally conductive sheet laminate in which adhesive films are laminated on both sides of a thermally conductive sheet,
   The thermally conductive sheet contains a binder resin made of silicone resin, carbon fibers, and a thermally conductive filler other than carbon fibers,
   The adhesive film contains a film-forming component, a liquid epoxy resin, and a curing agent,
   The thickness of the adhesive film is less than 20 μm,
   The thermally conductive sheet laminate, wherein the adhesive film has a viscosity at 20°C of greater than 8.0E+05 Pa·s and a viscosity at 130°C of less than 40 Pa·s.
2. The thermally conductive sheet laminate according to claim 1, wherein the adhesive film further contains a filler.
3. 3. The thermally conductive sheet laminate according to claim 1, having a thermal resistance of 0.4 cm ² K/W or less under a load of 1 kgf/cm ² .
4. The thermally conductive sheet laminate according to any one of claims 1 to 3, wherein the adhesive film has a thickness of 0.1 µm or more and 15 µm or less.
5. The thermally conductive sheet laminate according to any one of claims 1 to 4, wherein the adhesive film has a viscosity of 9.0E+05 Pa·s or more at 20°C.
6. The thermally conductive sheet laminate according to any one of claims 1 to 5, wherein the adhesive film has a viscosity of 10 Pa·s or more and 30 Pa·s or less at 130°C.
7. The ratio of the thickness (μm) of the adhesive film to the surface roughness Ra (μm) of the thermally conductive sheet (thickness of the adhesive film/surface roughness Ra of the thermally conductive sheet) is 0.003 to 0. The thermally conductive sheet laminate according to any one of claims 1 to 6, which is .7.
8. a heating element;
   and a radiator,
   An electronic device comprising the heat-generating body and the heat-dissipating body bonded with the thermally conductive sheet laminate according to any one of claims 1 to 7.
   

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