JP2022113002A - Joint sheet - Google Patents

Abstract

To provide a joint sheet including copper particles, which prevents a deterioration of its sinterability due to oxidation of the copper particles, allows formation of a compact and void-less joint layer, and enables electronic components and the like to be joined together with high strength.SOLUTION: A joint sheet 1 has copper particles 2, and a solvent 3 with a boiling point of 150°C or higher. The content ratio (mass ratio) of the copper particles 2 and the solvent 3 is 99:1-90:10. The copper particles 2 have a BET diameter of 40 nm or more and 750 nm or less. The solvent 3 has an OH group in its structure.SELECTED DRAWING: Figure 1

Description

The present invention relates to a joining sheet.

A bonding material is generally used to bond two or more components when assembling or mounting electronic components. As such a bonding material, a paste-like bonding material in which metal particles are dispersed in a solvent is known. When joining parts using a paste-like joining material, the joining material is applied to the surface of one part, the other part is brought into contact with the coated surface, and heated in this state to sinter the metal particles. It is possible to bond by forming a bonding layer on the substrate. Patent Literature 1 describes a paste of silver particles.

Also, as a bonding material, a sheet-like bonding material obtained by partially sintering metal particles is known. When joining parts using a sheet-shaped joining material, the joining material is placed between the parts and heated in this state to sinter the unsintered portion of the metal particles and form a joining layer. It can be joined by forming. A sheet-like bonding material is advantageous in that voids (bubbles) are less likely to be formed in the bonding layer because the solvent does not volatilize when heated compared to a paste-like bonding material. Patent Document 2 describes a sheet-like bonding material in which silver particles are sintered.

Japanese Patent No. 6428339 Japanese Patent No. 6245933

Silver is useful as a material for bonding materials such as electronic parts because of its excellent electrical conductivity and thermal conductivity. However, silver has the problem that ion migration and sulfuration are likely to occur. In particular, due to the recent narrowing of the pitch of electronic components and the thinning of wiring patterns, when ion migration or sulfurization occurs in the bonding layer, short circuits are likely to occur between pitches of electronic components or between wiring patterns. Therefore, it is conceivable to use copper as the material of the bonding material. In addition, copper is cheaper than silver and is useful for reducing the manufacturing cost of electronic parts. However, copper is more susceptible to oxidation than silver. For this reason, there is a problem that the bonding sheet in which the copper particles are sintered tends to be difficult to be sintered due to the oxidation of the copper particles.

The present invention has been made in view of the above-mentioned circumstances, and is a bonding sheet using copper particles, which is less likely to deteriorate in sinterability due to oxidation of copper particles, and is dense and has few voids. To provide a bonding sheet capable of forming a bond and bonding an electronic component or the like with high strength.

In order to solve the above problems, the bonding sheet of the present invention contains copper particles and a solvent having a boiling point of 150 ° C. or higher, and the content ratio of the copper particles and the solvent is 99: 1 in mass ratio. ˜90:10, the BET diameter of the copper particles is in the range of 40 nm or more and 750 nm or less, and the solvent has an OH group in its structure.

The bonding sheet of the present invention contains copper particles and a solvent, and since the copper particles are coated with the solvent, the copper particles are less likely to be oxidized. Moreover, since the solvent has a boiling point of 150° C. or higher, it is difficult to volatilize. Therefore, the bonding sheet of the present invention is less susceptible to deterioration in sinterability due to oxidation of copper particles, and has improved shape stability. Furthermore, the copper particles have a BET diameter in the range of 40 nm or more and 750 nm or less and are fine, so they have high sinterability, and the content ratio of the copper particles and the solvent is in the range of 99: 1 to 90: 10 by mass. Since the content of copper particles is 90% by mass or more, a dense sintered body (bonding layer) of copper particles can be formed by heating. In addition, since the content of the solvent is 10% by mass or less, the amount of volatile gas and decomposition gas generated from the solvent during heating is small. Moreover, the oxidation of the copper particles can be favorably suppressed by the solvent including an OH group in its structure. Therefore, according to the bonding sheet of the present invention, a dense bonding layer with few voids can be formed, and electronic components and the like can be bonded with high strength.

Moreover, in the bonding sheet of the present invention, the solvent preferably has a hydroxyl group or a carboxyl group. Oxidation of the copper particles can be more suitably suppressed by the solvent having a hydroxyl group. Oxidation of the copper particles can be suppressed more suitably by the solvent having a carboxyl group.

In the bonding sheet of the present invention, the solvent preferably contains at least one of a diol compound, a triol compound and a carboxylic acid. In this case, the diol compound, triol compound, and carboxylic acid have high adhesiveness to the copper particles, so they are difficult to volatilize over a long period of time. Therefore, deterioration of sinterability due to oxidation of copper particles can be suppressed over a long period of time, and the shape stability of the joining sheet is improved over a long period of time.

Moreover, in the bonding sheet of the present invention, the surfaces of the copper particles are preferably coated with an organic protective film. Oxidation of the copper particles can be suppressed by coating the surfaces of the copper particles with the organic protective film. In addition, the organic protective film can be appropriately detached during sintering by the solvent containing OH groups in the structure, and the decrease in the bonding strength of the bonding layer obtained by sintering the copper particles can be suppressed.

Here, in the bonding sheet of the present invention, the surface of the ^copper particles has a C ₃ H ₃ O ₃ ⁻ It is preferable that the ratio of the detected amount of ions is 0.001 or more.
When the ratio of the detected amount of C ₃ H ₃ O ₃ ⁻ ions to the detected amount of Cu ⁺ ions on the surface of the copper particles is 0.001 or more, the surfaces of the copper particles are appropriately coated with the organic protective film, Oxidation of the copper particles can be more suitably suppressed.

ADVANTAGE OF THE INVENTION According to the present invention, a bonding sheet using copper particles, which is less likely to deteriorate in sinterability due to oxidation of copper particles, can form a dense bonding layer with few voids, and can be used to bond electronic parts and the like with high strength. It is possible to provide a bonding sheet that can be bonded.

1 is a schematic cross-sectional view of a joining sheet according to one embodiment of the present invention; FIG. It is a flow figure showing a manufacturing method of a sheet for joining concerning one embodiment of the present invention. 1 is a schematic cross-sectional view of a joined body produced using a joining sheet according to an embodiment of the present invention; FIG.

A bonding sheet according to an embodiment of the present invention will be described below with reference to the accompanying drawings.
The bonding sheet of the present embodiment is, for example, placed between the substrate and the electronic component, and heated in this state to sinter the copper particles to form a bonding layer, thereby bonding the substrate and the electronic component together. It is used as a bonding material for forming a bonded body bonded via a bonding layer.

FIG. 1 is a schematic cross-sectional view of a joining sheet according to one embodiment of the present invention.
As shown in FIG. 1 , the bonding sheet 1 contains copper particles 2 and solvent 3 . The mass ratio of the copper particles 2 and the solvent 3 is 99:1 to 90:10 (=copper particles:solvent). That is, in the bonding sheet 1, the content of the copper particles 2 is within the range of 90% by mass or more and 99% by mass or less, and the content of the solvent 3 is within the range of 1% by mass or more and 10% by mass or less.

It is preferable that the bonding sheet 1 has a denseness within a range of 50% or more and 90% or less. The compactness is the proportion of the copper particles 2 spatially occupying the bonding sheet 1 . When the denseness is 60% or more, the adhesion between the copper particles 2 becomes high, so it becomes easier to form a dense bonding layer with few voids. In addition, when the density is 90% or less, the surface of the copper particles 2 can be covered with the solvent 3, so that the copper particles 2 are less likely to be oxidized, and the deterioration of the sinterability due to the oxidation of the copper particles is further suppressed. can do. The denseness is more preferably in the range of 55% or more and 75% or less, and particularly preferably in the range of 60% or more and 70% or less. The denseness of the bonding sheet 1 is determined by observing the cross section of the bonding sheet 1 with a scanning electron microscope (SEM), binarizing the obtained SEM image, and determining the space containing the copper particles 2 and the solvent 3. It can be calculated by dividing into parts. Specifically, it can be calculated by the method described in Examples described later.

The shape and size of the joining sheet 1 are not particularly limited. The joining sheet 1 may be, for example, a circular sheet with a diameter of 1 mm or more and 50 mm or a rectangular sheet with a side of 1 mm or more and 50 mm or less. Although the thickness of the joining sheet 1 is not particularly limited, it is preferably in the range of 50 μm or more and 1000 μm or less.

The copper particles 2 have a BET diameter within the range of 40 nm or more and 750 nm or less. The BET diameter is a particle diameter calculated from the BET specific surface area and the true density of the copper particles determined by the BET method, assuming that the copper particles 2 are spherical or cubic. Specifically, it can be determined by the method described in the examples below.

When the BET diameter of the copper particles 2 is 40 nm or more, it is difficult to form firm aggregates. Therefore, the surfaces of the copper particles 2 can be uniformly coated with the solvent 3 . On the other hand, when the BET diameter of the copper particles 2 is 750 nm or less, the reaction area is large and the sinterability by heating is high, so that a strong bonding layer can be formed. The BET diameter of the copper particles 2 is preferably 50 nm or more and 750 nm or less, more preferably 50 nm or more and 300 nm or less, more preferably 80 nm or more and 200 nm or less, and 80 nm or more and 170 nm or less. is particularly preferred.

The BET specific surface area of the copper particles 2 is preferably in the range of 2.0 m ² /g or more and 8.0 m ² /g or less, and is in the range of 3.5 m ² /g or more and 8.0 m ² /g or less. more preferably 4.0 m ² /g or more and 8.0 m ² /g or less is particularly preferable. Moreover, the shape of the copper particles 2 is not limited to a spherical shape, and may be a needle shape or a flat plate shape.

The surface of the copper particles 2 is preferably covered with an organic protective film, which is an organic film. By being coated with the organic protective film, the oxidation of the copper particles 2 is suppressed, and the deterioration of the sinterability due to the oxidation of the copper particles 2 is even less likely to occur. It can be said that the organic protective film covering the copper particles 2 is not formed by the solvent 3 and is not derived from the solvent 3 . Moreover, it can be said that the organic protective film covering the copper particles 2 is not a copper oxide film formed by oxidation of copper.

The fact that the copper particles 2 are coated with an organic protective film can be confirmed by analyzing the surfaces of the copper particles 2 using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Therefore, in the present embodiment, the copper particles 2 are C ₃ H ₃ O ₃ ⁻ ions relative to the detected amount of Cu ⁺ ions detected by analyzing the surface using time-of-flight secondary ion mass spectrometry. (C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio) is preferably 0.001 or more. More preferably, the C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio is in the range of 0.05 or more and 0.2 or less. In addition, the surface of the copper particle 2 in this analysis is not the surface of the copper particle 2 when the organic protective film is removed from the copper particle 2, but the surface of the copper particle 2 containing the covering organic protective film (i.e. surface of the organic protective film).

By analyzing the surface of the copper particles 2 using time-of-flight secondary ion mass spectrometry, C ₃ H ₄ O ₂ ^- ions and C ₅ or higher ions may be detected. The ratio of the detected amount of C ₃ H ₄ O ₂ ⁻ ions to the detected amount of Cu ⁺ ions (C ₃ H ₄ O ₂ ⁻ /Cu ⁺ ratio) is preferably 0.001 or more. Further, the ratio of the detected amount of C5 or higher ions to the detected amount of Cu ⁺ ions _{( C5} or higher ions/Cu ⁺ ratio) is preferably less than 0.005.

The C ₃ H ₃ O ₃ ^- ions, C ₃ H ₄ O ₂ ^- ions, and C ₅ or higher ions detected in the time-of-flight secondary ion mass spectrometry are the organic protective film covering the surface of the copper particles 2 . derived from the membrane. Therefore, when each of the C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio and the C ₃ H ₄ O ₂ ⁻ /Cu ⁺ ratio is 0.001 or more, the surface of the copper particle 2 becomes difficult to oxidize, and the copper particle 2 becomes difficult to aggregate. Further, when the C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio and the C ₃ H ₄ O ₂ ⁻ /Cu ⁺ ratio are 0.2 or less, the sinterability of the copper particles 2 is not excessively lowered, and the copper particles Oxidation and agglomeration of 2 can be suppressed, and generation of decomposition gas from the organic protective film during heating can be suppressed, so that a bonding layer with few voids can be formed. In order to further improve the oxidation resistance during storage of the copper particles 2 and to further improve the sinterability at low temperatures, the C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio and the C ₃ H ₄ O ₂ The ⁻ /Cu ⁺ ratio is preferably in the range of 0.08 to 0.16. In addition, when the C ₅ or higher ion/Cu ⁺ ratio is 0.005 times or higher, a large amount of organic protective film having a relatively high desorption temperature exists on the particle surface, and as a result, sufficient sinterability cannot be expressed. Therefore, it is difficult to obtain a strong bonding layer. Preferably, the _C5 and above ions/Cu ⁺ ratio is less than 0.003.

The organic protective film is preferably derived from citric acid. A method for producing the copper particles 2 coated with an organic protective film derived from citric acid will be described later. The coating amount of the organic protective film on the copper particles 2 is preferably in the range of 0.5% by mass or more and 2.0% by mass or less with respect to 100% by mass of the copper particles, and 0.8% by mass or more and 1.8% by mass. It is more preferably in the range of 0.8% by mass or more and 1.5% by mass or less. When the coating amount of the organic protective film is 0.5% by mass or more, the copper particles 2 can be uniformly coated with the organic protective film, and oxidation of the copper particles 2 can be suppressed more reliably. In addition, since the coating amount of the organic protective film is 2.0% by mass or less, the generation of voids in the sintered body (bonding layer) of the copper particles due to the gas generated by the decomposition of the organic protective film due to heating is prevented. can be suppressed. The coating amount of the organic protective film can be measured using a commercially available device. Specifically, it can be measured by the method described in Examples described later.

When the copper particles 2 are heated at a temperature of 300° C. for 30 minutes in an inert gas atmosphere such as argon gas, 50% by mass or more of the organic protective film is preferably decomposed. The organic protective film derived from citric acid generates carbon dioxide gas, nitrogen gas, evaporative gas of acetone and water vapor when decomposed.

The copper particles 2 coated with an organic protective film derived from citric acid can be produced, for example, as follows. First, an aqueous dispersion of copper citrate is prepared, and a pH adjuster is added to the aqueous dispersion of copper citrate to adjust the pH to 2.0 or more and 7.5 or less. Next, in an inert gas atmosphere, 1.0 to 1.2 equivalents of a hydrazine compound capable of reducing copper ions was added as a reducing agent to the pH-adjusted copper citrate aqueous dispersion. to mix. The resulting mixed solution is heated to a temperature of 60° C. or higher and 80° C. or lower in an inert gas atmosphere and held for 1.5 hours or longer and 2.5 hours or shorter. As a result, the copper ions eluted from the copper citrate are reduced to form the copper particles 2 , and an organic protective film derived from citric acid is formed on the surfaces of the copper particles 2 .

An aqueous dispersion of copper citrate is prepared by adding powdered copper citrate to pure water such as distilled water or ion-exchanged water so that the concentration is 25% by mass or more and 40% by mass or less, and using a stirring blade. It can be prepared by stirring and dispersing uniformly. Examples of pH adjusters include triammonium citrate, ammonium hydrogen citrate, and citric acid. Of these, triammonium citrate is preferred because it facilitates mild pH adjustment. The reason why the pH of the copper citrate aqueous dispersion is 2.0 or more is that the elution rate of copper ions eluted from the copper citrate is increased, the generation of copper particles is rapidly advanced, and the target fine copper is obtained. This is so that particles 2 can be obtained. The reason why the pH is set to 7.5 or less is to suppress eluted copper ions from becoming copper (II) hydroxide, thereby increasing the yield of the copper particles 2 . Moreover, by setting the pH to 7.5 or less, it is possible to prevent the reducing power of the hydrazine compound from becoming excessively high, making it easier to obtain the target copper particles 2 . The pH of the copper citrate aqueous dispersion is preferably adjusted within the range of 4 or more and 6 or less.

Reduction of copper citrate with a hydrazine compound is carried out under an inert gas atmosphere. This is to prevent oxidation of copper ions dissolved in the liquid. Examples of inert gases include nitrogen gas and argon gas. A hydrazine compound has advantages such as not producing a residue after a reduction reaction when copper citrate is reduced in an acidic environment, relatively high safety, and easy handling. The hydrazine compound includes hydrazine monohydrate, anhydrous hydrazine, hydrazine hydrochloride, hydrazine sulfate, and the like. Among these hydrazine compounds, preferred are hydrazine monohydrate and anhydrous hydrazine, which do not contain impurities such as sulfur and chlorine.

In general, copper generated in an acid solution with a pH of less than 7 dissolves. However, in the present embodiment, a hydrazine compound, which is a reducing agent, is added to and mixed with an acidic liquid having a pH of less than 7, and the copper particles 2 are generated in the resulting mixed liquid. Therefore, the citric acid-derived component generated from the copper citrate quickly coats the surfaces of the copper particles 2, so that the dissolution of the copper particles 2 is suppressed. The aqueous dispersion of copper citrate after adjusting the pH is preferably kept at a temperature of 50° C. or higher and 70° C. or lower to facilitate the progress of the reduction reaction.

Heating the mixed liquid in which the hydrazine compound is mixed in an inert gas atmosphere to a temperature of 60° C. or more and 80° C. or less and holding it for 1.5 hours or more and 2.5 hours or less is to generate the copper particles 2 and to generate This is to form and cover the surfaces of the copper particles 2 with an organic protective film. The purpose of heating and holding in an inert gas atmosphere is to prevent oxidation of the generated copper particles 2 . Copper citrate, which is a starting material, usually contains about 35% by mass of a copper component. A hydrazine compound, which is a reducing agent, is added to a copper citrate aqueous dispersion containing such a copper component, heated to the above temperature, and held for the above time to generate copper particles 2, Since the formation of the organic protective film on the surface of the copper particles 2 progresses in a well-balanced manner, the coating amount of the organic protective film is in the range of 0.5% by mass or more and 2.0% by mass or less with respect to 100% by mass of the copper particles. It is possible to obtain the copper particles 2 inside. If the heating temperature is less than 60° C. and the holding time is less than 1.5 hours, the copper citrate is not completely reduced, and the generation rate of the copper particles 2 becomes too slow, resulting in the formation of the organic protective film covering the copper particles 2. The amount may be excessive. On the other hand, if the heating temperature exceeds 80° C. and the holding time exceeds 2.5 hours, the generation rate of the copper particles 2 may become too fast, and the amount of the organic protective film covering the copper particles 2 may become too small. . A preferred heating temperature is 65° C. or higher and 75° C. or lower, and a preferred holding time is 2 hours or longer and 2.5 hours or shorter.

The copper particles 2 produced in the mixed liquid are solid-liquid separated from the mixed liquid in an inert gas atmosphere, for example, using a centrifuge, and dried by a freeze-drying method or a reduced-pressure drying method. A copper particle 2 coated with an organic protective film is obtained. Since the surface of the copper particles 2 is covered with an organic protective film, the copper particles 2 are not easily oxidized even if they are stored in the atmosphere until they are used as a bonding sheet.

Solvent 3 acts as a binder for copper particles 2 . Moreover, the solvent 3 acts as an antioxidant that coats the copper particles 2 to prevent oxidation of the copper particles 2 .

Solvent 3 has a boiling point of 150° C. or higher. Therefore, the solvent 3 is difficult to volatilize and is retained in the bonding sheet 1 for a long period of time. The upper limit of the boiling point of the solvent 3 is a temperature lower than the temperature at which the bonding sheet 1 is heated to sinter the copper particles 2 . The boiling point of solvent 3 is preferably 200° C. or lower.

Solvent 3 is preferably liquid at room temperature. Solvent 3 preferably has a freezing point of 30° C. or higher. When the solvent 3 is liquid at room temperature, the copper particles 2 and the solvent 3 can be easily mixed in the production of the bonding sheet 1 .

Solvent 3 preferably has a molecular weight of 1000 or less. When solvent 3 is a polymeric compound, the molecular weight is the number average molecular weight. By setting the molecular weight of the solvent 3 to 1000 or less, it is possible to suppress the solvent from remaining in the bonding layer after heating, thereby suppressing the generation of voids. Moreover, the solvent 3 is preferably an organic solvent having a molecular weight of 100 or more and 1000 or less. By using an organic solvent having the above molecular weight as the solvent 3, the surfaces of the copper particles 2 can be uniformly coated with the solvent 3 by mixing the copper particles 2 and the solvent 3, and the bonding sheet 1 can be stored. Sometimes it becomes difficult for the solvent to flow out. In addition, since the above organic solvent has a boiling point within an appropriate range, it is possible to suppress shape change due to evaporation of the solvent and drying of the sheet during storage, and after heating, the solvent penetrates into the bonding layer. Remaining can be suppressed. The molecular weight of the organic solvent is more preferably in the range of 200 or more and 800 or less, and particularly preferably in the range of 200 or more and 600 or less.

Solvent 3 is a compound having an OH group at its terminal, and can be said to contain an OH group in its structure. Oxidation of the copper particles 2 can be suppressed by having an OH group. Furthermore, the solvent 3 preferably contains a hydroxyl group as a reducing group. A hydroxyl group is an OH group itself. A carboxyl group (COOH group) includes an OH group in its structure. The solvent 3 can suppress oxidation of the copper particles by containing a carboxyl group. The solvent 3 may contain both hydroxyl groups and carboxyl groups, and preferably contains at least one of hydroxyl groups and carboxyl groups. In order to sinter the copper particles 2, the organic protective film on the surfaces of the copper particles 2 must be removed by heating or the like. On the other hand, the sinterability of the copper particles 2 from which the organic protective film has been removed tends to deteriorate due to oxidation, and the bonding strength of the bonding layer (copper sintered body) obtained by sintering the copper particles 2 tends to decrease. By using a solvent containing an OH group, the organic protective film can be appropriately detached during heating for sintering, and a decrease in the bonding strength of the bonding layer obtained by sintering the copper particles 2 can be suppressed. preferable. Moreover, by using a solvent having an OH group as the solvent 3, the oxidation of the copper particles 2 can be suppressed, and the decrease in the bonding strength of the bonding layer obtained by sintering the copper particles 2 can be suppressed. In addition, since a solvent having an OH group generally tends to have a high boiling point, in the bonding sheet 1 using a solvent having a hydroxyl group, the solvent 3 is difficult to volatilize, and the shape stability of the sheet is further improved. In addition, since the solvent 3 contains a carboxyl group, it is possible to suppress the oxidation of the copper particle surface and appropriately suppress the decrease in bonding strength.

The solvent 3 preferably has a dielectric constant of 4 or more and 80 or less, more preferably 10 or more and 45 or less, and even more preferably 20 or more and 40 or less. When the dielectric constant is within this numerical range, it is possible to appropriately exhibit reducibility and suppress oxidation of the copper particles 2 . The dielectric constant may be measured with a liquid dielectric constant meter (Model 871, manufactured by Nihon Luft Co., Ltd.).

As the solvent 3, for example, it is preferable to use at least one of a monool, a diol compound, a triol compound, a polyol compound, and a carboxylic acid, and more preferably at least one of a diol compound, a triol compound, and a carboxylic acid. preferable. Examples of diol compounds include ethylene glycol, diethylene glycol and polyethylene glycol. Examples of triol compounds include glycerin, butanetriol and polyoxypropylenetriol. Moreover, it is preferable to use a monool, a polyol, or a carboxylic acid as the solvent 3 . Examples of polyol compounds include "2-ethyl-1,3-hexanediol". Examples of monols are dodecanol, tetradecanol, hexadecanol. Examples of carboxylic acids include hexanoic acid, octanoic acid, octylic acid and decanoic acid. One of these organic solvents and polymer solvents may be used alone, or two or more thereof may be used in combination. By using such a solvent, it is possible to appropriately exhibit reducing properties and suppress oxidation of the copper particles 2 .

Next, a method for manufacturing the bonding sheet 1 of this embodiment will be described.
FIG. 2 is a flowchart showing a method for manufacturing a joining sheet according to one embodiment of the present invention.
The joining sheet of this embodiment can be manufactured by a method including a mixing step and a molding step, as shown in FIG.

The mixing step S<b>01 is a step of mixing the copper particles 2 and the solvent 3 . A rotation-revolution mixer or a planetary mixer can be used for mixing the copper particles 2 and the solvent 3 .

The forming step S02 is a step of forming the mixture obtained in the mixing step S01 into a sheet.
As a method for forming the mixture into a sheet, a rolling method using a pressure roller or a pressing method using a mold can be used.

The bonding sheet 1 can be obtained by cutting the sheet-shaped mixture adjusted to a predetermined thickness as described above into a predetermined shape.

Next, a method for manufacturing a bonded body using the bonding sheet of the present embodiment will be described. FIG. 3 is a schematic cross-sectional view of a joined body produced using the joining sheet according to one embodiment of the present invention.
As shown in FIG. 3, the bonded body 11 includes a substrate 12, a bonding layer 13, and an electronic component . The substrate 12 and the electronic component 14 are bonded via the bonding layer 13 .

As the substrate 12, for example, a printed wiring board having an insulating plate and a wiring pattern formed on the insulating plate can be used. The printed wiring board is not particularly limited, and flexible printed wiring boards, rigid printed wiring boards, and rigid flexible printed wiring boards can be used.

As the electronic component 14, for example, semiconductor elements, resistors, capacitors, and crystal oscillators can be used. Examples of semiconductor elements include SBD (Schottky Barrier Diode), MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), LSI (Large Scale Integration), LED chip, LED-CSP (LED- Chip Size Package).

The bonded body 11 is obtained by arranging the bonding sheet described above between the substrate 12 and the electronic component 14 to obtain a laminate, heating the obtained laminate, and burning the copper particles of the bonding sheet. It can be manufactured by bonding to form the bonding layer 13 . The heating temperature of the laminate is, for example, within the range of 150° C. or higher and 300° C. or lower. The heating time for the laminate is, for example, in the range of 10 minutes or more and 1 hour or less. It is preferable to heat the laminate while pressurizing the laminate in the lamination direction of the laminate in an inert gas atmosphere. Nitrogen gas and argon gas can be used as the inert gas. The pressure applied to the laminate is preferably in the range of 0.5 MPa or more and 30 MPa or less.

The bonding sheet 1 of the present embodiment configured as described above contains the copper particles 2 and the solvent 3, and the copper particles 2 are coated with the solvent 3, so that the copper particles 2 are less likely to be oxidized. Moreover, since the boiling point of the solvent 3 is 150° C. or higher, it is difficult to volatilize. Therefore, the bonding sheet 1 of the present embodiment is less likely to deteriorate in sinterability due to oxidation of the copper particles 2, and has improved shape stability. Moreover, since the solvent 3 has an OH group in its structure, the oxidation of the copper particles 2 can be suitably suppressed. Furthermore, the copper particles 2 have a BET diameter in the range of 40 nm or more and 750 nm or less and are fine, so they have high sinterability, and the content ratio of the copper particles 2 and the solvent 3 is 99: 1 to 90: 10 by mass. and the content of the copper particles 2 is 90% by mass or more, a dense sintered body (bonding layer) of the copper particles 2 can be formed by heating. In addition, since the content of the solvent 3 is 10% by mass or less, the amount of volatile gas and decomposition gas generated from the solvent during heating is small. Therefore, according to the bonding sheet 1 of the present embodiment, deterioration of sinterability due to oxidation of copper particles is unlikely to occur, a dense bonding layer with few voids can be formed, and electronic components and the like can be bonded with high strength. can.

In addition, in the bonding sheet 1 of the present embodiment, the surfaces of the copper particles 2 are coated with an organic protective film. Since the surfaces of the copper particles 2 of the bonding sheet 1 are coated with an organic protective film, the copper particles are less likely to be oxidized. When the copper particles are oxidized, the copper oxide film reduces the bondability. Therefore, by making the copper particles less likely to be oxidized with the organic protective film as in the present embodiment, the decrease in bondability can be suppressed. Moreover, the solvent 3 containing a reducing group can appropriately detach the organic protective film during sintering, thereby suppressing a decrease in the bonding strength of the bonding layer obtained by sintering the copper particles 2 .

In addition, in the bonding sheet 1 of the present embodiment, the surface of the ^copper particles has a C ₃ H ₃ O ₃ ⁻ It is preferable that the ratio of the detected amount of ions is 0.001 or more. When the ratio of the detected amount of C ₃ H ₃ O ₃ ⁻ ions to the detected amount of Cu ⁺ ions is 0.001 or more, the surfaces of the copper particles are appropriately coated with the organic protective film, and the copper particles are protected. Oxidation can be more suitably suppressed.

In the bonding sheet 1 of the present embodiment, when the solvent 3 has a hydroxyl group, the solvent 3 has a reducing property, so oxidation of the copper particles 2 is less likely to occur. Moreover, since the solvent 3 is a carboxyl group, the surface of the copper particles is changed to thermally decomposable copper acetate, so that the deterioration of the sinterability due to the oxidation of the copper particles 2 can be further suppressed.

Further, in the bonding sheet 1 of the present embodiment, when the reducing group of the solvent 3 is a hydroxyl group or a carboxyl group, the affinity for the copper particles is high. Solvent 3 becomes difficult to volatilize. Therefore, deterioration of the sinterability due to oxidation of the copper particles 2 can be further suppressed, and the shape stability of the joining sheet 1 is further improved.

Furthermore, in the bonding sheet 1 of the present embodiment, when the solvent 3 contains at least one of a diol compound, a triol compound, and a carboxylic acid, the diol compound, the triol compound, and the carboxylic acid are compatible with the copper particles 2. Due to its high adhesiveness, it is difficult to volatilize over a long period of time. Therefore, deterioration of sinterability due to oxidation of copper particles can be suppressed over a long period of time, and the shape stability of the joining sheet is improved over a long period of time.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and can be modified as appropriate without departing from the technical idea of the invention.
For example, as the bonded body 11 using the bonding sheet 1 of the present embodiment, FIG. Applications are not limited to this. For example, the joining sheet 1 can be used when joining two substrates. Specifically, it can be used when bonding a base substrate and a substrate (submount substrate) relatively smaller in size than the base substrate. Moreover, in a power module, it can be used when joining a ceramic circuit board incorporating a plurality of semiconductor elements and a heat sink. Moreover, the bonding sheet 1 can be used when bonding an LED element and a submount substrate in an LED device.

[Production of copper particles A]
Copper citrate 2.5 hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and ion-exchanged water are stirred and mixed using a stirring blade to obtain an aqueous dispersion of copper citrate having a concentration of 30% by mass. prepared. Next, an ammonium citrate aqueous solution as a pH adjuster was added to the obtained aqueous copper citrate dispersion to adjust the pH of the aqueous copper citrate dispersion to 5. Next, the resulting copper citrate aqueous dispersion was heated to 50° C., and while maintaining that temperature, an aqueous hydrazine monohydrate solution (diluted twice as a reducing agent for copper ions) was placed under a nitrogen gas atmosphere. ) was added all at once, and stirred and mixed using a stirring blade. The amount of the hydrazine monohydrate aqueous solution added was 1.2 equivalents of the amount required to reduce the total amount of copper ions. The resulting mixed solution was heated to 70° C. in a nitrogen gas atmosphere and held at that temperature for 2 hours to generate copper particles. The produced copper particles were recovered using a centrifuge. The recovered copper particles were dried by a vacuum drying method to produce copper particles A.

[Production of copper particles B]
Copper particles B were produced in the same manner as the production of copper particles A, except that the pH of the copper citrate aqueous dispersion was adjusted to 2.0.

[Production of copper particles C]
Copper particles C were produced in the same manner as the production of copper particles A, except that the pH of the copper citrate aqueous dispersion was adjusted to 7.5.

[Preparation of copper particles D]
Copper particles D were produced in the same manner as the production of copper particles A, except that the pH of the copper citrate aqueous dispersion was adjusted to 1.7.

[Production of copper particles E]
Copper particles E were produced in the same manner as the production of copper particles A, except that the pH of the copper citrate aqueous dispersion was adjusted to 8.0.

[Production of copper particles F]
Copper fine particles F were produced in the same manner as copper particles A except that RCV11 (Type-B) manufactured by DOWA Electronics Co., Ltd. was used.

The BET diameter and coating layer components of the obtained copper particles A to F were measured by the following methods. The results are shown in Table 1 below.

(BET diameter)
Using a specific surface area measuring device (Quantachrome Instruments, QUANTACHROME AUTOSORB-1), the amount of nitrogen gas adsorbed by the copper particles was measured, and the specific surface area of the copper particles was determined by the BET method. Using the obtained specific surface area S (m ² /g) and the density ρ (g/cm ³ ) of the copper particles, the BET diameter was calculated from the following formula.
BET diameter (nm) = 6000/(ρ (g/cm ³ ) x S (m ² /g))

(Component of coating layer)
Using a time-of-flight secondary ion mass spectrometer (TOF-SIMS: nanoTOFII, manufactured by ULVAC PHI), C ₃ H ₃ O ₃ ^- ions and C ₃ H ₄ O ₂ ^- ions for Cu ⁺ ions, C ₅ or higher ions detected. Specifically, a sample for measurement was obtained by embedding copper powder in the surface of the In foil. A TOF-SIMS spectrum was obtained under the conditions that the measurement range was 100 μm square, the primary ion was Bi ₃ ⁺⁺ (30 kV), and the measurement time was 5 minutes. From the obtained TOF-SIMS spectrum, the detected amounts of Cu ⁺ , C ₃ H ₃ O ₃ ^- ions, C ₃ H ₄ O ₂ ^- ions, and C ₅ or higher ions were determined, and the detected amount of each ion was calculated as Cu The C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio, the C ₃ H ₄ O ₂ ⁻ /Cu ⁺ ratio, and the C ₅ and above ions/Cu ⁺ ratio were calculated by dividing by the detected amount of ⁺ ions.

(Coating amount)
Using a differential thermal balance TG8120-SL (manufactured by RIGAKU), the coating amount of the copper particles was measured. As a sample, copper particles from which moisture was removed by freeze-drying were used. In order to suppress the oxidation of copper particles, measurement was performed in nitrogen (G2 grade) gas, the temperature increase rate was 10 ° C./min, and the weight loss rate when heated from 250 ° C. to 300 ° C. defined as That is, the coating amount=(sample weight after measurement)/(sample weight before measurement)×100 (wt %). The measurement was performed three times for each copper particle of the same lot, and the arithmetic average value was taken as the coating amount.

[Invention Example 1]
Copper particles and polyethylene glycol (molecular weight: 200) as a binder were mixed at a mass ratio of 95:5. Also, the dielectric constant of the binder was measured. The dielectric constant was measured at 22° C. with a liquid dielectric constant meter (Model 871, manufactured by Nihon Luft Co., Ltd.).
Next, the obtained mixture is rolled using a powder rolling mill (2RM-63K, manufactured by Ohno Roll Co., Ltd.) having a pressure roller under the condition of a pressure roller gap width of 500 μm to obtain a thickness of 500 μm. of copper sheets were obtained. The compactness of the obtained copper sheet was measured by the following method. Also, the shear strength and void fraction of a joined body produced using the obtained copper sheets were measured by the following methods. Table 2 shows the results.

(Compactness)
After sealing the copper sheet with epoxy resin, the copper sheet was cut horizontally with respect to the thickness direction of the copper sheet. A cross-section of the copper sheet was obtained by mechanically polishing and cross-polishing the cut surface of the copper sheet. Then, the cut surface of the copper sheet was observed at 50,000 times using a SEM (scanning electron microscope). The resulting SEM image was binarized using image processing software (ImageJ manufactured by the National Institutes of Health, USA), divided into a particle portion and a void portion, and the denseness was calculated from the following formula.
Density (%) = (total area of particle part / (total area of particle part + total area of pore part)) x 100

Density was measured for 10 SEM images taken at random. The values shown in Table 2 are average values of denseness calculated from 10 SEM images.

(Shear strength of zygote)
A copper sheet piece (2.5 mm square×500 μm thick) was produced by cutting the copper sheet using a commercially available cutter knife. The above copper sheet piece (2.5 mm square×500 μm thickness) was placed on an oxygen-free copper substrate of 30 mm square×1 mm thickness. Next, an oxygen-free copper dummy element of 2.5 mm square and 1 mm thick was placed on the copper sheet piece. Thus, a laminate was obtained in which the oxygen-free copper substrate and the oxygen-free copper dummy element were laminated via the copper sheet piece. Using a die bonder (manufactured by Alpha Design Co., Ltd., HTB-MM), the obtained laminate was held for 15 minutes under the conditions of a pressure of 5 MPa and a temperature of 250 ° C. in a nitrogen gas atmosphere to obtain a 2.5 mm square. A joined body (Sample A) in which the oxygen-free copper substrate and the oxygen-free copper dummy element were joined through the copper joining layer was produced.

The shear strength of the resulting joined body (Sample A) was measured by a method conforming to JIS Z 3198-7 (Lead-free solder test method-Part 7: Chip component solder joint shear test method). Specifically, a load was applied to the oxygen-free copper dummy element using a bond tester (SERIES 4000 manufactured by Nordson DAGE), and the load (maximum shear load) when the oxygen-free copper dummy element was peeled off from the copper bonding layer. was measured. The moving speed of the tool was set to 50 μm/sec, and the gap between the tip of the tool and the oxygen-free copper substrate was set to 50 μm. The shear strength (unit: MPa) was obtained by converting the obtained maximum shear load into Newton and dividing it by the area of the copper bonding layer (2.5 mm×2.5 mm). Seven joined bodies were produced, and the shear strength of each joined body was measured. The values shown in Table 2 are the average shear strength of seven zygotes. Those with a shear strength of 20 MPa or more are good, and those with a shear strength of less than 20 MPa are unacceptable.

(Void fraction of bonded body)
A copper sheet piece (10 mm square×500 μm thick) was produced by cutting the copper sheet using a commercially available cutter knife. The above copper sheet piece (10 mm square×500 μm thick) was placed on an oxygen-free copper substrate of 30 mm square×1 mm thick. Next, an oxygen-free copper dummy element of 10 mm square and 1 mm thick was placed on the copper sheet piece. Thus, a laminate was obtained in which the oxygen-free copper substrate and the oxygen-free copper dummy element were laminated via the copper sheet piece. Using a die bonder (manufactured by Alpha Design Co., Ltd., HTB-MM), the obtained laminate was held for 15 minutes under the conditions of a pressure of 5 MPa and a temperature of 250 ° C. in a nitrogen gas atmosphere to obtain a 2.5 mm square. A joined body (Sample B) in which the oxygen-free copper substrate and the oxygen-free copper dummy element were joined through the copper joining layer was produced.

An ultrasonic flaw detection image of the copper bonding layer portion of the obtained bonded body (sample B) was measured using an ultrasonic flaw detector (FINE-SAT, manufactured by Hitachi High-Technologies Corporation). The obtained ultrasonic flaw detection image is binarized using image processing software (ImageJ manufactured by the National Institutes of Health, USA), divided into voids (cavities) and joined bodies (copper particle sintered bodies), and the following equation The void fraction was calculated from
Void ratio (%) = (total area of void portions/area of copper bonding layer (10 mm x 10 mm)) x 100

Seven joined bodies were produced, and the void fraction was measured for each joined body. The values shown in Table 2 are the average void fraction of seven joints. A void ratio of less than 10% is good, and a void ratio of 10% or more is unsatisfactory.

[Invention Examples 2 to 17, Comparative Examples 1 to 5]
A copper sheet was prepared in the same manner as in Inventive Example 1, except that the type of copper particles, the type of binder, the boiling point, the number average molecular weight, and the blending amounts of the copper particles and the binder were changed as shown in Table 2 below. made. In Table 2, PEG represents polyethylene glycol, DEG represents diethylene glycol, and EG represents ethylene glycol. Then, in the same manner as in Inventive Example 1, the denseness of the obtained copper sheet was measured, and the shear strength and void ratio of a joined body produced using the obtained copper sheet were measured. Table 2 shows the results.

A copper particle having a BET diameter in the range of 40 nm or more and 750 nm or less and a solvent having a boiling point of 150 ° C. or more as a binder and having an OH group are mixed in a mass ratio of 99: 1 to 90: 10 (copper particles: solvent ), all of the joined bodies using the copper sheets of Examples 1 to 17 of the present invention have a high shear strength of 15 MPa or more and a low void ratio of less than 10%. It can be seen that the sinterability is less likely to deteriorate due to oxidation, a dense bonding layer with few voids can be formed, and electronic parts and the like can be bonded with high strength.

On the other hand, the bonded body using the copper sheet of Comparative Example 1 containing polyethylene glycol, which is solid at room temperature as a binder, has a greatly reduced shear strength, a greatly increased void ratio, and a dense bonding layer with few voids. I know it can't be formed. This is probably because the polyethylene glycol did not volatilize and remained in the bonding layer during heating for manufacturing the bonded body. In addition, it can be seen that the joined body using the copper sheet of Comparative Example 2 containing ethanol having a boiling point of 80° C. as a binder has an increased void ratio and cannot form a dense joining layer with few voids. It is considered that the holes were enlarged due to the temporary volatilization of ethanol during the heating in the production of the joined body.

In Comparative Example 3, in which the content ratio of polyethylene glycol as a binder exceeded the upper limit of the present invention, the copper sheet obtained by rolling adhered to the surface of the pressure roller of the powder rolling mill with strong adhesion. When the copper sheet was peeled off from the pressure roller, the copper sheet was damaged, and the copper sheet with the minimum required size for manufacturing the bonded body could not be recovered. could not. In Comparative Example 4, in which the content ratio of polyethylene glycol as a binder was below the lower limit of the present invention, many cracks occurred in the copper sheet obtained by the rolling treatment. The cracks damaged the copper sheet, making it impossible to recover a copper sheet having the minimum dimensions necessary to produce a bonded body. Therefore, the shear strength and void fraction of the bonded body could not be evaluated. In Comparative Example 5, in which tetradecane having no OH group was used as a solvent, the shear strength deteriorated, the void ratio increased, and oxidation of the copper particles could not be suppressed, resulting in a decrease in sinterability. It can be seen that a joining layer with few voids cannot be formed.

REFERENCE SIGNS LIST 1 bonding sheet 2 copper particles 3 solvent 11 bonded body 12 substrate 13 bonding layer 14 electronic component

Claims (5)

Containing copper particles and a solvent having a boiling point of 150° C. or higher,
The content ratio of the copper particles and the solvent is 99:1 to 90:10 in mass ratio,
The BET diameter of the copper particles is in the range of 40 nm or more and 750 nm or less,
A bonding sheet, wherein the solvent has an OH group in its structure. The joining sheet according to claim 1, wherein the solvent has a hydroxyl group or a carboxyl group. The joining sheet according to claim 1 or 2, wherein the solvent contains at least one of a diol compound, a triol compound and a carboxylic acid. The joining sheet according to any one of claims 1 to 3, wherein the surfaces of the copper particles are coated with an organic protective film. The surface of the copper particles has a ratio of a detected amount of C ₃ H ₃ O ₃ ⁻ ions to a detected amount of Cu ⁺ ions detected by time-of-flight secondary ion mass spectrometry of 0.001 or more. The joining sheet according to claim 4, wherein

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