JP2020164974A - Silver paste and method for producing the same, and method for producing joined body - Google Patents

Abstract

To provide a silver paste in which a joining layer having few voids can be made by using the same.SOLUTION: The present invention is a silver paste, containing a silver powder, a fatty acid silver, and an aliphatic amine. Further, the silver powder contains a first silver particle having a particle size of 100 nm or more and less than 500 nm in a range of 55 vol% or more and 95 vol% or less, contains a second silver particle having a particle size of 50 nm or more and less than 100 nm in a range of 5 vol% or more and 40 vol% or less, and contains a third silver particle having a particle size of less than 50 nm in a range of 5 vol% or less.SELECTED DRAWING: Figure 1

Description

The present invention manufactures a silver paste used as a raw material for producing a bonding layer for bonding a circuit board and a high-power LED element and a bonding layer for bonding a circuit board and a power semiconductor chip, and the silver paste. The present invention relates to a method and a method for producing a bonded body bonded by a bonding layer produced by using this silver paste.

Conventionally, in order to bond and fix (die bond) a semiconductor chip to a metal plate such as a lead frame, a silver paste containing Ag powder, a thermosetting resin, and a solvent has been used. For example, the thermally conductive composition disclosed in Patent Document 1 contains silver powder, silver fine particles, fatty acid silver, amine and silver resinate. The silver powder has an average particle size of 0.3 μm to 100 μm. The silver fine particles have an average particle diameter of primary particles of 50 to 150 nm, a crystallite diameter of 20 to 50 nm, a ratio of the average particle diameter to the crystallite diameter of 1 to 7.5, and a silver resinate. A thermally conductive composition containing (see, for example, Patent Document 1) is disclosed.

It is said that the heat conductive composition configured in this way can obtain a heat conductor having a high thermal conductivity.

Japanese Patent No. 5872545 (Claim 1, paragraph [0006], FIG. 1)

However, in the heat conductive composition shown in Patent Document 1, a relatively large amount of deficiency is contained in the heat conductor produced by using this heat conductive composition, as shown in FIG. 1 of Patent Document 1. Since there are (voids), there is a problem that the heat conduction characteristics of the heat conductor are low accordingly.

A first object of the present invention is to provide a silver paste and a method for producing the same, which can produce a bonding layer having few voids. A second object of the present invention is to provide a silver paste and a method for producing the silver paste, which can improve the thermal cycle characteristics of the bonding layer produced by using the silver paste. A third object of the present invention is to provide a silver paste and a method for producing the silver paste, which can adjust the viscosity of the silver paste to facilitate operations such as coating. A fourth object of the present invention is to provide a silver paste and a method for producing the silver paste, which can improve the heat conduction characteristics of the bonding layer produced by using the silver paste. A fifth object of the present invention is to provide a method for producing a bonded body, which can improve the heat conduction characteristics and the cold heat cycle characteristics of the bonded body by improving the heat conduction characteristics and the cold heat cycle characteristics of the bonded layer.

The first aspect of the present invention is a silver paste containing silver powder, fatty acid silver, and an aliphatic amine, and the silver powder contains 55% by volume or more of first silver particles having a particle size of 100 nm or more and less than 500 nm. 5 volumes of 3rd silver particles containing 95% by volume or less and having a particle size of 50 nm or more and less than 100 nm containing 5% by volume or more and 40% by volume or less and having a particle size of less than 50 nm. It is characterized by including in the range of% or less.

The second aspect of the present invention is an invention based on the first aspect, and is characterized by further containing a resin.

The third aspect of the present invention is an invention based on the first aspect, and is characterized by further containing a solvent.

A fourth aspect of the present invention is an invention based on the first aspect, further comprising a complex formed by reacting at least a part of silver fatty acid and at least a part of an aliphatic amine. To do.

A fifth aspect of the present invention is that when the total amount of the fatty acid silver, the aliphatic amine and the solvent is 100% by mass, the fatty acid silver is 0.1. A step of mixing at a ratio of mass% to 40% by mass, the aliphatic amine of 0.1% by mass to 60% by mass, and the solvent of 80% by mass or less to obtain a mixture, and the mixture at 30 ° C. to 100 ° C. A method for producing a silver paste, which comprises a step of heating, stirring, and then cooling to obtain a mixed solution, and a step of kneading the mixed solution and silver powder to obtain a silver paste, wherein the silver powder has a particle size. The first silver particles having a particle size of 100 nm or more and less than 500 nm are contained in the range of 55% by volume or more and 95% by volume or less, and the second silver particles having a particle size of 50 nm or more and less than 100 nm are contained in the range of 5% by volume or more and 40% by volume or less. It is characterized by containing third silver particles having a particle size of less than 50 nm in a range of 5% by volume or less.

A sixth aspect of the present invention is the step of preparing the first member and the second member, and the silver according to any one of the first to fourth aspects on the surface of the first member and / or the second member. A step of applying a paste or a silver paste produced by the method according to claim 5 to form a silver paste layer, and laminating the first member and the second member via the silver paste layer to prepare a laminate. By heating the laminate, the first silver particles, the second silver particles, and the third silver particles in the silver paste layer are sintered to form a bonding layer, and the first member and the second member are formed. It is a method of manufacturing a bonded body including a step of producing a bonded body bonded via a bonded layer.

In the silver paste according to the first aspect of the present invention, the silver powder contains first silver particles having a particle size of 100 nm or more and less than 500 nm in a range of 55% by volume or more and 95% by volume or less, and the particle size is 50 nm or more and less than 100 nm. Since certain second silver particles are contained in the range of 5% by volume or more and 40% by volume or less and third silver particles having a particle size of less than 50 nm are contained in the range of 5% by volume or less, the silver powder has a relatively wide particle size distribution. By having the particles, the gaps between the first to third silver particles become small and dense during sintering, so that a bonding layer with few voids can be produced.

In the silver paste according to the second aspect of the present invention, since the silver paste further contains a resin, the thermal cycle characteristics of the bonding layer prepared by using the silver paste can be improved.

In the silver paste according to the third aspect of the present invention, since the silver paste further contains a solvent, an excellent effect that the viscosity of the silver paste can be adjusted to facilitate operations such as coating can be obtained.

Since the silver paste of the fourth aspect of the present invention contains a complex formed by reacting at least a part of fatty acid silver and at least a part of an aliphatic amine, fine silver is precipitated from the complex at the time of firing. By filling the space between the first silver particles, the second silver particles, and the third silver particles in the silver paste, the bonded layer produced by using the silver paste becomes more dense and its heat. Conduction characteristics can be dramatically improved.

In the method for producing a silver paste according to the fifth aspect of the present invention, a mixed solution in which a mixture of fatty acid silver, an aliphatic amine and a solvent is mixed at a predetermined ratio is heated and stirred, and then cooled to prepare a mixed solution. And silver powder are kneaded to prepare a silver paste, and the silver powder contains first silver particles having a particle size of 100 nm or more and less than 500 nm in a range of 55% by volume or more and 95% by volume or less, and has a particle size of 50 nm or more and 100 nm. Since the second silver particles having a particle size of less than 50% by volume are contained in the range of 5% by volume or more and 40% by volume or less and the third silver particles having a particle size of less than 50 nm are contained in the range of 5% by volume or less, the silver powder is similarly described above. Since the particles have a relatively wide particle size distribution, the gaps between the first to third silver particles become small and dense during sintering, so that a bonding layer with few voids can be produced.

In the method for producing a bonded body according to the sixth aspect of the present invention, the first member and the second member are laminated with the silver paste layer coated with the silver paste sandwiched between them to prepare a laminated body, and the laminated body is formed. By heating, the first silver particles, the second silver particles, and the third silver particles in the silver paste layer are sintered to form a bonding layer, and the first member and the second member are bonded via the bonding layer. Since the bonded body is produced, the bonding layer for joining the bonded body has few voids, and the heat conduction characteristics and the cold cycle characteristics of the bonded body produced by this method can be improved.

FIG. 5 is a FE-SEM (Field Emission-Scanning Electron Microscope) photographic view of a bonding layer produced by the silver paste of Example 15. It is FE-SEM photograph figure of the bonding layer prepared by the silver paste of Example 16. It is FE-SEM photograph figure of the bonding layer prepared by the silver paste of Example 17. It is FE-SEM photograph figure of the bonding layer prepared by the silver paste of Comparative Example 3.

Next, a mode for carrying out the present invention will be described. The silver paste contains silver powder, fatty acid silver and aliphatic amines. The silver powder contains first silver particles (first group of silver particles), second silver particles (second group of silver particles), and third silver particles (third group of silver particles) having different particle sizes. , All of these 1st to 3rd silver particles aggregate with each other as primary particles to form an agglomerate (silver powder). The first silver particles have a particle size of 100 nm or more and less than 500 nm, and include 55% by volume or more and 95% by volume or less with respect to 100% by volume of the total amount of the first to third silver particles. The second silver particles have a particle size of 50 nm or more and less than 100 nm, and are contained in a range of 5% by volume or more and 40% by volume or less with respect to 100% by volume of the total amount of the first to third silver particles. Further, the third silver particles have a particle size of less than 50 nm and are contained in a range of 5% by volume or less with respect to 100% by volume of the total amount of the first to third silver particles. The "volume" here indicates the volume of the silver particles themselves. Here, the content ratio of the first to third silver particles is limited to the above range because the particle size distribution is relatively wide, so that the gaps between the first to third silver particles are formed during sintering. This is because a bonding layer with few voids can be produced by forming small and dense aggregates. The purity of silver in the first to third silver particles is preferably 90% by mass or more, and more preferably 99% by mass or more. This is because the higher the purity of the first to third silver particles, the easier it is to melt, so that the first to third silver particles can be sintered at a relatively low temperature. The object of the present invention can be achieved even if the elements other than silver in the first to third silver particles include Au, Cu, Pd and the like.

Further, the first silver particles having a particle size of 100 nm or more and less than 500 nm are preferably contained in the range of 70% by volume or more and 90% by volume or less, and the second silver particles having a particle size of 50 nm or more and less than 100 nm are 10% by volume or more. It is preferably contained in the range of 30% by volume or less, and the third silver particles having a particle size of less than 50 nm are preferably contained in the range of 1% by volume or less. When the particle size distribution of the first to third silver particles is within the above range, the effect of forming a dense agglomerate of silver powder with a small gap between the first to third silver particles during sintering becomes high. In addition, a bonding layer with less voids can be produced. The particle size of the first to third silver particles can be obtained by measuring the projected area of the first to third silver particles in the silver powder using, for example, a SEM (Scanning Electron Microscope). It can be obtained by calculating the equivalent circle diameter (the diameter of a circle having the same area as the projected area of the 1st to 3rd silver particles) from the projected area and converting the calculated particle size into the volume-based particle size. it can. An example of a specific measurement method will be described in Examples described later.

The silver powder preferably contains an organic substance composed of an organic reducing agent or a decomposition product thereof, and the organic substance is preferably decomposed or volatilized at a temperature of 150 ° C. Examples of organic reducing agents include ascorbic acid, formic acid, tartaric acid and the like. The organic substance composed of the organic reducing agent or its decomposition product is stored in the state of secondary particles in which the first to third silver particles are aggregated (that is, silver powder before preparing the silver paste), and the first to third silver particles are stored. It has the effect of suppressing the oxidation of the surface of the 3 silver particles and suppressing the mutual diffusion of the 1st to 3rd silver particles, that is, the diffusion bonding during storage. Further, the organic substance is easily decomposed or volatilized when a silver paste containing an aggregate of silver particles is printed on the surface to be bonded of the member to be bonded and heated, and the high activity of the first to third silver particles is achieved. By exposing the surface, there is an effect of facilitating the sintering reaction between the first to third silver particles. Further, the decomposition product or volatile substance of the organic substance has a reducing ability to reduce the oxide film on the surface to be bonded of the member to be bonded. If the organic matter contained in the silver powder remains in the bonding layer, it may be decomposed with the passage of time to generate voids in the bonding layer. Therefore, the content ratio of the organic substance is preferably 2% by mass or less with respect to 100% by mass of the total amount of the first to third silver particles. However, in order to obtain the effect of the organic substance, the content ratio of the organic substance is preferably 0.05% by mass or more with respect to 100% by mass of the total amount of the first to third silver particles. The content ratio of the organic substance is more preferably 0.1% by mass to 1.5% by mass with respect to 100% by mass of the total amount of the first to third silver particles.

In the present invention, the silver powder before being mixed with each component described later is a state of secondary particles in which first to third silver particles (primary particles) are aggregated, and is a volume-based measurement measured by a laser diffraction / scattering method. In the particle size distribution curve, D10 is in the range of 0.05 μm or more and 0.25 μm or less, D50 is in the range of 0.4 μm or more and 0.6 μm or less, and D90 is in the range of 1.5 μm or more and 2.5 μm or less. It is preferable to have. In the silver paste of the present invention obtained from the silver powder having such a relatively wide particle size distribution and each component described later, a dense aggregate having a small gap between the first to third silver particles at the time of sintering. The effect of forming the paste is increased, and a bonding layer with few voids can be produced. Here, the volume-based particle size distribution is measured by the laser diffraction / scattering method as follows. First, 0.1 g of silver powder (secondary particles) is put into 20 g of ion-exchanged water, and ultrasonic waves of 25 kHz are irradiated for 5 minutes to disperse the silver powder in the ion-exchanged water. Next, an appropriate amount of the obtained dispersion of silver powder is dropped onto an observation cell of a laser diffraction / scattering type particle size distribution measuring device (trade name: LA-960 manufactured by HORIBA, Ltd.), and the particle size distribution is measured according to the procedure of this device. The particle size distribution measured by this laser diffraction / scattering method is the particle size distribution of the secondary particles in which the first to third silver particles (primary particles) are aggregated.

Moreover, aggregates of the first to third silver particles, it is preferred that the specific surface area is in the range of 2m ² / g~8m ² / g, in the range of 3m ² / g~7m ² / g further preferable. Here, the agglomerates of the first to third silver particles having a specific surface area within the above range are baked at a relatively low temperature because the reaction area of the first to third silver particles is large and the reactivity by heating is high. Can be tied.

On the other hand, examples of the fatty acid silver include silver acetate, silver oxalate, silver propionate, silver myristate, and silver butyrate. Examples of the aliphatic amine include primary amines, secondary amines, and tertiary amines. The number of carbon atoms of the aliphatic amine is preferably 8 to 12. If the number of carbon atoms is too small, the boiling point of the aliphatic amine tends to be low, which may reduce the printability of the silver paste. If the number of carbon atoms is too large, the sintering of silver particles in the silver paste may be hindered, and a bonded body having sufficient strength may not be obtained. As a specific example, the primary amine includes ethylhexylamine, aminodecane, dodecylamine, nonylamine, hexylamine and the like, the secondary amine includes dimethylamine, diethylamine and the like, and the tertiary amine includes dimethylamine and diethylamine. , Trimethylamine, triethylamine and the like.

Here, in the silver paste, the molar ratio of the aliphatic amine to the fatty acid silver, that is, the molar amount of the aliphatic amine / the molar amount of the fatty acid silver may be in the range of 1.5 to 3. When the proportion of the aliphatic amine is small, the proportion of the solid fatty acid silver is relatively high, so that it is difficult to disperse uniformly in the silver paste, and voids may easily occur inside the bonding layer obtained by heating. There is. If the proportion of the aliphatic amine is too large, the excessive amount of the aliphatic amine causes the grain growth of the silver powder in the silver paste, and the paste viscosity is lowered, so that the printability may be deteriorated. The molar amount of the aliphatic amine / the molar amount of the silver fatty acid is preferably in the range of 1.7 to 2.8, and more preferably in the range of 2.0 to 2.5.

Further, the silver paste preferably contains a complex formed by reacting at least a part of fatty acid silver with at least a part of an aliphatic amine. This complex is presumed to be a silver amine complex.

The silver paste preferably further contains either one or both of the resin and the solvent. Examples of the resin include epoxy-based resins, silicone-based resins, acrylic-based resins, and mixtures thereof. Epoxy resins include bisphenol A type epoxy resins, novolak type epoxy resins, cyclic aliphatic epoxy resins, and mixtures thereof, and silicone resins include methyl silicone resins, epoxy modified silicone resins, and polyester modified silicones. There are resins and mixtures thereof, and acrylic resins include acrylate-based monomer resins and the like. These resins are cured by heating the silver paste, and the cured product is filled in the voids of the sintered body of the silver powder. By filling the voids of the sintered body of silver powder with the cured product of the thermosetting resin composition, the mechanical strength of the bonding layer is improved, and the decrease in bonding strength under a thermal cycle load is suppressed. The content of the resin may be in the range of 0.1% by mass to 3% by mass when the whole silver paste is 100% by mass. If the content of the resin is less than 0.1% by mass, the mechanical strength of the bonding layer may not be improved, and if it exceeds 3% by mass, sintering of silver powder is hindered and the mechanical strength of the bonding layer is lowered. There is a risk. The content of the resin may be preferably in the range of 0.2% by mass to 2.5% by mass, and more preferably in the range of 0.3% by mass to 2.0% by mass. Good.

Examples of the solvent include alcohol-based solvents, glycol-based solvents, acetate-based solvents, hydrocarbon-based solvents, and mixtures thereof. Alcohol-based solvents include α-terpineol, isopropyl alcohol, ethylhexanediol, and mixtures thereof, and glycol-based solvents include ethylene glycol, diethylene glycol, polyethylene glycol, and mixtures thereof, and acetate-based solvents. Examples include butyl carbitol acetate and the like, and examples of the hydrocarbon solvent include decane, dodecane, tetradecane, and a mixture thereof.

A method for producing the silver paste thus constructed will be described. First, when fatty acid silver, an aliphatic amine and a solvent are prepared and the total amount of the fatty acid silver, the aliphatic amine and the solvent is 100% by mass, for example, fatty acid silver is 0.1% by mass to 40% by mass. The aliphatic amine is mixed in a proportion of 0.1% by mass to 60% by mass, and the solvent is mixed in a proportion of 80% by mass or less. Here, the mixing ratio of the fatty acid silver, the aliphatic amine and the solvent is limited to the above range because the effect of the present invention can be obtained without causing precipitation or the like in the mixed solution. More preferably, when the total amount of the fatty acid silver, the aliphatic amine and the solvent is 100% by mass, the fatty acid silver is 20% by mass to 30% by mass, the aliphatic amine is 20% by mass to 40% by mass, and the solvent is It is mixed at a ratio of 40% by mass to 60% by mass.

Next, the mixture is heated to 30 ° C. to 100 ° C. and stirred for 5 minutes to 10 hours to prepare a mixed solution, and then the mixed solution is lowered to room temperature (25 ° C.). As a result, a mixed solution of fatty acid silver, an aliphatic amine and a solvent (also simply referred to as a mixed solution) is prepared. Here, the heating temperature and heating time of the mixture are within the above ranges in order to uniformly mix the fatty acid silver, the aliphatic amine and the solvent. A solvent is not always required. For example, when the aliphatic amine is liquid at room temperature, a mixed solution can be prepared by mixing the fatty acid silver and the aliphatic amine without using a solvent.

Next, the mixed solution and the silver powder are kneaded, then stirred with a planetary planetary stirrer or the like, and further kneaded with a three-roll mill or the like to obtain a silver paste. Here, when the silver paste is 100% by mass, the content of the silver powder may be in the range of 50% by mass to 95% by mass, and the balance may be the mixed solution. Preferably, the content of the silver powder is 80% by mass to 90% by mass. In the silver paste, if the content of the silver powder is low, the viscosity of the silver paste may decrease and coating defects such as sagging may easily occur, and if it is too high, the viscosity may increase and the handleability may deteriorate. The silver paste does not have to contain a solvent. Moreover, the silver paste may contain the resin. In this case, the cold cycle characteristics are improved.

In this mixed solution, the molar ratio of the aliphatic amine to the silver fatty acid, that is, the molar amount of the aliphatic amine / the molar amount of the silver fatty acid is preferably in the range of 1.5 to 3, 1.7. It is more preferably within the range of ~ 2.8. When a silver paste is prepared using such a mixed solution, the molar ratio of the aliphatic amine to the fatty acid silver in the mixed solution becomes the molar ratio of the aliphatic amine to the fatty acid silver in the silver paste.

The procedure for producing a bonded body using the silver paste will be described. First, a first member and a second member to be joined to each other are prepared. Examples of the first member include a Si wafer having a gold-plated outermost surface, and examples of the second member include a Cu plate having a silver-plated outermost surface. However, it is not limited to these. Next, the silver paste is applied to the surface of the first member and / or the second member by, for example, a metal mask method or the like to form a silver paste layer having a desired planar shape. Next, the first member and the second member are laminated via the silver paste layer to prepare a laminated body. Then, by firing this laminate, that is, by heating and holding the laminate at a temperature of 120 ° C. to 280 ° C. (heating temperature) for 10 minutes to 240 minutes (heating time), the first silver in the silver paste layer. The particles, the second silver particles, and the third silver particles are sintered to form a bonding layer, and a bonded body in which the first member and the second member are bonded via the bonding layer is produced. Here, the reason why the heating temperature and heating time of the laminate are limited to the above ranges is that sintering may be difficult to proceed in less than 10 minutes, and even if it exceeds 240 minutes, the bonding characteristics do not change and the cost increases. Based on the reason that It is preferable that the laminate is only heated without pressurization. This is based on the reason that the process is simplified and the cost is reduced.

Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, silver acetate (fatty acid silver), aminodecane (aliphatic amine) and butyl carbitol acetate (solvent) are prepared, and when the total amount of fatty acid silver, aliphatic amine and solvent is 100% by mass, silver acetate (fatty acid). 22% by mass of silver), 41.3% by mass of aminodecane (aliphatic amine), and 36.7% by mass of butyl carbitol acetate (solvent) were set aside, and these were placed in a glass container together with a stirrer of Stirrer. Then, the container was placed on a hot plate heated to 50 ° C., and the stirrer was stirred for 1 hour while rotating at 300 rpm to prepare a mixed solution. The container in which the mixture was stored was then removed from the hot plate to reduce the temperature of the mixture to room temperature. As a result, a fatty acid silver / aliphatic amine mixed solution (hereinafter, simply referred to as a mixed solution) was prepared. This mixed solution was designated as Example 1.

<Examples 2 to 14 and Comparative Examples 1 to 2>
As the mixed solution of Examples 2 to 14 and Comparative Examples 1 and 2, the types shown in Table 1 are used as the fatty acid silver, the aliphatic amine and the solvent, and the fatty acid silver, the aliphatic amine and the solvent are shown in Table 1. Each was blended in the proportions shown. Although it is not a mixed solution because Comparative Example 1 does not contain silver fatty acid and Comparative Example 2 does not contain an aliphatic amine, Comparative Examples 1 and 2 are also referred to as mixed solutions in the present specification for convenience. Further, in the column of the type of fatty acid silver in Table 1, "A1" is silver acetate, "A2" is silver oxalate, and "A3" is silver myristate. Further, in the column of the type of aliphatic amine in Table 1, "B1" indicates aminodecane, "B2" indicates hexylamine, "B3" is nonylamine, and "B4" is dodecylamine. Further, in the solvent type column in Table 1, "C1" is butylcarbitol acetate, "C2" is ethylene glycol, "C3" is terpineol, and "C4" is 2-ethyl1, It is 3-hexanediol.

<Comparative test 1 and evaluation>
The mixed solutions of Examples 1 to 14 and Comparative Examples 1 and 2 were heated to 130 ° C. for 10 minutes with stirring, and then 1 g of this mixed solution was dropped onto a silicon wafer and dried under reduced pressure at a temperature of 25 ° C. A wafer in which the dried product adhered to the surface was produced. Then, the surface of this wafer was observed by SEM (scanning electron microscope), 1000 particles adhering to the surface were counted, and extracted using image processing software (Image-J (American National Institute of Public Health: development)). The projected area of the particles (primary particles) was measured, and the equivalent circle diameter was calculated from the obtained projected area, which was used as the primary particle diameter. For particles with invisible contours, the equivalent circle diameter was not measured. The obtained primary particle size was converted into a volume-based particle size, and the average value of the volume-based particle size was taken as the average particle size of the dried product. Further, the product in which silver powder was generated from the dried product was determined to be "possible", and the product in which silver powder was not produced from the dried product or the silver powder could not be measured was determined to be "impossible". Table 2 shows the average particle size of the dried product and the determination results. Table 2 also shows the types of silver fatty acids, the types of aliphatic amines, and the types of solvents.

As is clear from Table 2, since the mixed solution of Comparative Example 1 containing no fatty acid silver does not contain silver, which is expected to contribute to the densification of the bonding layer, silver powder is generated during SEM (scanning electron microscope) observation. It was not seen and the judgment result was impossible.

Further, in the mixed solution of Comparative Example 2 containing no aliphatic amine, a uniform mixed solution could not be obtained, and the dried product on the silicon wafer became a lump. Therefore, silver powder is measured by SEM (scanning electron microscope) observation. The judgment result was impossible. It is considered that this is because in Comparative Example 2, since the aliphatic amine was not contained, the decomposition of the fatty acid silver did not proceed sufficiently.

On the other hand, in the mixed solution of Examples 1 to 14 containing the fatty acid silver and the aliphatic amine, the generation of silver powder having an average particle size of 50 nm to 100 nm was observed during SEM (scanning electron microscope) observation, and the determination result was acceptable. It was. It is presumed that this is because Examples 1 to 14 contain fatty acid silver and an aliphatic amine, so that the organic matter is rapidly decomposed by heating, and highly active surface-exposed silver nanoparticles are easily formed. To.

<Example 15>
In order to make the silver paste 100% by mass, 25% by mass of the mixed solution of Example 1 and 75% by mass of silver powder (aggregates of first to third silver particles) are kneaded and then stirred with a planetary planetary stirrer. Then, the mixture was further kneaded with a three-roll mill. This gave a silver paste. This silver paste was designated as Example 15.

The No. 1 silver powder (mixture / aggregate of the first to third silver particles) shown in Table 5 was prepared as follows. First, silver fine particles having D10, D50 and D90 of 20 nm, 50 nm and 100 nm, respectively, and silver fine particles having D10, D50 and D90 of 150 nm, 300 nm and 500 nm, respectively, were prepared. D10, D50 and D90 of the silver fine particles were obtained from the particle size distribution curve of the silver fine particles. The particle size distribution curve of the silver fine particles was measured by the dynamic light scattering method described later. The prepared silver fine particles (raw material powder A) in which D10, D50 and D90 are 20 nm, 50 nm and 100 nm, respectively, and silver fine particles (raw material powder B) in which D10, D50 and D90 are 150 nm, 300 nm and 500 nm, respectively, are used. , The mixture was mixed at a mass ratio of 1: 3 to obtain a silver fine particle mixture. The raw material powders A and B can be produced as follows. For the raw material powder A, for example, silver nitrate, citric acid, and potassium hydroxide are mixed in distilled water so as to have an equimolar ratio (1: 1: 1) with respect to silver ions in silver nitrate to prepare a suspension. did. Hydrazine acetate is added to this suspension in a molar ratio of 2 to 1 silver ion. It can be obtained by reacting a suspension to which hydrazine acetate is added at a liquid temperature of 40 ° C., and washing, recovering, and drying from the obtained reaction liquid slurry. For the raw material powder B, for example, a silver nitrate aqueous solution, ammonia water, and distilled water are mixed to prepare a silver ammine aqueous solution having a silver concentration of 22 g / L, and a reducing solution is added to the silver ammine aqueous solution to obtain a resulting silver particle slurry. Obtained by washing, collecting and drying. The reducing solution is a mixed solution of a hydroquinone aqueous solution and a sodium hydroxide aqueous solution, and is a solution prepared so that the redox potential is -380 mV based on Ag / AgCl.

<Measurement method of particle size distribution curve by dynamic light scattering method>
First, 0.1 g of silver fine particles was put into 20 g of ion-exchanged water, and ultrasonic waves of 25 kHz were irradiated for 5 minutes to disperse the silver fine particles in the ion-exchanged water. Next, the obtained dispersion of silver fine particles was poured into an observation cell for a dynamic light scattering type particle size distribution measuring device (HORIBA, Ltd .: LB-550), and the particle size distribution was measured according to the procedure of this device.

The silver fine particle mixture, sodium ascorbate (organic reducing agent), and water were mixed at a mass ratio of 10: 1: 89 to prepare a silver fine particle slurry. The silver fine particle slurry was heated at a temperature of 90 ° C. for 3 hours to reduce the silver fine particles. Next, the silver fine particle slurry was allowed to cool to room temperature, and then the solid matter was separated and recovered using a centrifuge. The recovered solid matter (mercury-containing fine particle aggregate) was washed with water several times and dried to obtain No. 1 silver powder (mixture of first to third silver particles) shown in Table 5.

The No. 2 silver powder has a mass ratio of 1: 1 except that the mixing ratio of the silver particles having a D50 of 50 nm and the silver particles having a D50 of 300 nm is 1: 1 in the above-mentioned method for preparing the No. 1 silver powder. Was obtained in the same manner by the method for preparing No. 2 silver powder.

The silver powder of No. 3 is different from the above-mentioned method of preparing the silver powder of No. 1 in that the mixing ratio of the silver particles having a D50 of 50 nm and the silver particles having a D50 of 300 nm was set to 1: 5 by mass ratio. Was obtained in the same manner by the method for preparing No. 3 silver powder.

No. 4 silver powder was obtained by the following method. A 900 g silver nitrate aqueous solution held at 50 ° C. and a 600 g sodium citrate aqueous solution kept at 50 ° C. were simultaneously added dropwise to 1200 g of ion-exchanged water held at 50 ° C. over 5 minutes to prepare a silver citrate slurry. Prepared. The ion-exchanged water was continuously stirred while the silver nitrate aqueous solution and the sodium citrate aqueous solution were simultaneously added dropwise to the ion-exchanged water. The concentration of silver nitrate in the silver nitrate aqueous solution was 66% by mass, and the concentration of citric acid in the sodium citrate aqueous solution was 56% by mass. Then, 300 g of an aqueous sodium formate solution kept at 50 ° C. was added dropwise to the silver citrate slurry held at 50 ° C. over 30 minutes to obtain a mixed slurry. The concentration of formic acid in this aqueous sodium formate solution was 58% by mass. Next, the mixed slurry was subjected to a predetermined heat treatment. Specifically, the mixed slurry was raised to a maximum temperature of 60 ° C. at a heating rate of 10 ° C./hour, held at 60 ° C. (maximum temperature) for 30 minutes, and then lowered to 20 ° C. over 60 minutes. .. As a result, a silver powder slurry was obtained. The silver powder slurry was placed in a centrifuge and rotated at a rotation speed of 1000 rpm for 10 minutes. As a result, the liquid layer in the silver powder slurry was removed to obtain a dehydrated and desalted silver powder slurry. The dehydrated and desalted silver powder slurry was dried by a freeze-drying method for 30 hours to obtain No. 4 silver powder.

The No. 5 silver powder has a mass ratio of 2: 1 except that the mixing ratio of the silver particles having a D50 of 50 nm and the silver particles having a D50 of 300 nm is set to 2: 1 in the above-mentioned method for preparing the No. 1 silver powder. Was obtained in the same manner by the method for preparing silver powder of No. 5.

The silver powder of No. 6 has a mass ratio of 1: 6 other than the mixing ratio of the silver particles having a D50 of 50 nm and the silver particles having a D50 of 300 nm in the above-mentioned method for preparing the silver powder of No. 1. Was obtained in the same manner by the method for preparing silver powder of No. 6.

The silver powder of No. 7 is different from the above-mentioned method of preparing the silver powder of No. 1 in that the mixing ratio of the silver particles having a D50 of 50 nm and the silver particles having a D50 of 300 nm was set to a mass ratio of 2: 9. Was obtained in the same manner by the method for preparing silver powder of No. 7.

The No. 8 silver powder was obtained in the same manner as in the No. 8 silver powder preparation method, except that only silver particles having a D50 of 50 nm were used in the above-mentioned No. 1 silver powder preparation method.

The silver powder of No. 9 is different from the above-mentioned method of preparing the silver powder of No. 1 in that the mixing ratio of the silver particles having a D50 of 50 nm and the silver particles having a D50 of 300 nm was set to 4: 3 by mass ratio. Was obtained in the same manner by the method for preparing silver powder of No. 9.

The silver powder of No. 10 is different from the above-mentioned method of preparing the silver powder of No. 1 in that the mixing ratio of the silver particles having a D50 of 50 nm and the silver particles having a D50 of 300 nm was set to 1: 9 by mass ratio. Was obtained in the same manner by the method for preparing No. 10 silver powder.

With respect to the obtained silver powder, the particle size distribution of the silver particles (first to third silver particles) constituting the silver powder and the content of organic substances contained in the silver powder were measured by the following methods.

<Measurement method of particle size distribution of silver particles>
Using SEM, 500 images of aggregates (secondary particles) in which the first to third silver particles are aggregated are acquired, and the particle size of the silver particles (primary particles) contained in each silver particle aggregate is determined. It was measured. At this time, the device magnification of the SEM was set to 100,000 times. From the SEM image of 500 silver particle aggregates, silver particles in which the entire outline of the silver particles (primary particles) can be visually recognized were extracted. Next, the projected area of the extracted silver particles was measured using image processing software (Image-J), the equivalent circle diameter was calculated from the obtained projected area, and this was used as the particle size of the silver particles. The diameter equivalent to the circle was not measured for silver particles whose contours were not visible. The particle size of the obtained silver particles was converted into a volume-based particle size, and the particle size distribution of the volume-based particle size was obtained. The results are shown in Table 5.

<Measuring method of organic matter content>
The silver powder before mixing with the mixed solution was weighed and heated in the air at a temperature of 150 ° C. for 30 minutes. After heating, the mixture was allowed to cool to room temperature, and the mass of silver powder was measured. The content of organic matter was calculated from the following formula (1). As a result, the content of organic matter was 0.2% by mass.
Organic matter content (mass%) = {(AB) / A} × 100 …… (1)
However, A in the formula (1) is the mass of the silver powder before heating, and B is the mass of the silver powder after heating. The results obtained are shown in Table 5.

<Examples 16 to 33 and Comparative Examples 3 to 8>
As the silver pastes of Examples 16 to 33 and Comparative Examples 3 to 8, the fatty acid silver, aliphatic amines and solvent types shown in Table 1 were used as the mixed solution, and the silver powder and the mixed solution were used in Tables 3 and 4. The silver paste was prepared in the same manner as in Example 15 except for the formulations shown in Tables 3 and 4, respectively. The mixed solutions used in Examples 15 to 33 and Comparative Examples 3 to 8 are shown in any of Examples 1 to 14 in the column of mixed solution types in Tables 3 and 4. Further, in Examples 15 to 33 and Comparative Examples 3 to 8, any one of 10 types (No. 1 to No. 10) of silver powder having different particle size distributions shown in Table 5 is blended, and Examples 15 to 15 to The silver powder used in 33 and Comparative Examples 3 to 8 is shown by any of No. 1 to No. 10 in the column of the type of silver powder in Tables 3 and 4.

<Comparative test 2 and evaluation>
(1) Bonds were prepared using the silver pastes of Examples 15 to 33 and Comparative Examples 3 to 8, respectively. Specifically, first, a 2.5 mm square Si wafer (thickness: 200 μm) with gold plating on the outermost surface was prepared as the first member, and 20 mm with silver plating on the outermost surface as the second member. A square Cu plate (thickness: 1 mm) was prepared. Next, the silver paste was applied to the surface of the second member by the metal mask method to form a silver paste layer. Next, the first member was placed on the silver paste layer to prepare a laminated body. Further, by firing the laminate, that is, by holding the laminate at a temperature (heating temperature) of 150 ° C. for 60 minutes (heating time), the first member and the second member are bonded via the bonding layer. did. These joints were used as the joints of Examples 15 to 33 and Comparative Examples 3 to 8. The laminate was not pressurized. The joint strength of these joints was measured as follows.

(1-1) Method for measuring joint strength of joints The joint strengths of the joints of Examples 15 to 33 and Comparative Examples 3 to 8 were measured using a shear strength evaluation tester. Specifically, the joint strength is measured by fixing the first member (Cu plate) of the joint body horizontally and using a share tool at a position 50 μm above the surface (upper surface) of the joint layer to measure the second member (Si wafer). ) Was pushed from the side to the horizontal direction, and the strength when the second member was broken was measured. The moving speed of the share tool was 0.1 mm / sec. The strength test was performed three times under one condition, and the arithmetic mean value was used as the measured value of the joint strength.

(2) Silver fired films were prepared using the silver pastes of Examples 15 to 33 and Comparative Examples 3 to 8, respectively. Specifically, first, the silver pastes of Examples 15 to 33 and Comparative Examples 3 to 8 are applied on a transparent glass plate with a metal mask plate (hole size: length 10 mm × width 10 mm, thickness: 50 μm) to silver. Each paste layer was formed. Next, the silver paste layer formed on the transparent glass substrate was fired, that is, the silver paste layer was held at a temperature of 150 ° C. (heating temperature) for 60 minutes (heating time) to prepare a silver fired film. .. These silver-fired films were used as the silver-fired films of Examples 15 to 33 and Comparative Examples 3 to 8. The thermal diffusivity of these fired silver films was measured as follows.

(2-1) Method for Measuring Thermal Diffusivity of Silver-Fired Film The thermal diffusivity of the silver-fired films of Examples 15 to 33 and Comparative Examples 3 to 8 was measured by a laser flash method. Specifically, first, the temperature change T (t) on the back surface of the silver fired film when the surface of the silver fired film was uniformly irradiated with a pulse laser and instantaneously heated was measured. Next, since the temperature change T (t) on the back surface of the silver fired film is expressed by a one-dimensional heat conduction equation, the temperature change T (t) on the back surface of the silver fired film is taken on the vertical axis and the elapsed time t is horizontal. By taking the axis, a (T (t) -t) curve was obtained, and the time t _0.5 required to reach half the maximum temperature rise temperature T _{MAX was} calculated from this curve. Then, the thermal diffusivity α of the silver fired film was obtained by the following equation (2).
α = 1.370 x L ² / (π ² x t _0.5 ) …… (2)
L in the formula (2) is the thickness of the silver fired film. These results are shown in Table 1.

As is clear from Table 4, when the bonded body and the silver-fired film were prepared using the silver paste of Comparative Example 3 to which the fatty acid silver was not added, the bonding strength of the bonded body was as small as 20 MPa, and the heat of the silver-fired film was small. The diffusivity was as small as 78 W / mK. Further, in Comparative Example 4 in which the aliphatic amine was not added, the silver paste was not obtained, so that the bonded body and the silver fired film could not be prepared. To these, the conjugate and silver firing were used using the silver pastes of Examples 15 to 33 in which silver acetate, silver oxalate or silver myristate was added as silver fatty acid, and aminodecane, hexylamine or nonylamine were added as aliphatic amines. When the film was prepared, the bonding strength of the bonded body was as large as 38 MPa to 50 MPa, and the thermal diffusivity of the silver-fired film was as large as 122 W / mK to 155 W / mK.

When a bonded body and a silver fired film were prepared using the silver paste of Comparative Example 5 in which the number of silver particles having a particle size of 50 nm or more and less than 100 nm was as small as 1% by volume, the bonding strength of the bonded body was as small as 20 MPa and silver fired. The thermal diffusivity of the film was as small as 119 W / mK.

Using the silver paste of Comparative Example 6 in which silver particles having a particle size of 50 nm or more and less than 100 nm are as many as 50% by volume and silver particles having a particle size of less than 50 nm as many as 10% by volume, the bonded body and the silver fired film are prepared. When produced, the bonding strength of the bonded body was as small as 10 MPa, and the thermal diffusion rate of the silver fired film was as small as 80 W / mK.

When a bonded body and a silver-fired film were prepared using the silver paste of Comparative Example 7 in which the amount of silver particles having a particle size of less than 50 nm was as large as 7% by volume, the bonding strength of the bonded body was as small as 15 MPa, which was the same as that of the silver-fired film. The thermal diffusivity was as small as 90 W / mK.

When a bonded body and a silver fired film were prepared using the silver paste of Comparative Example 8 containing 100% by volume of silver particles having a particle size of 100 nm or more and less than 500 nm as silver powder, the bonding strength of the bonded body was as small as 11 MPa.

As is clear from Table 3, the silver powder contains first silver particles having a particle size of 100 nm or more and less than 500 nm in a range of 55% by volume or more and 95% by volume or less, and second silver having a particle size of 50 nm or more and less than 100 nm. Joined body and silver using the silver paste of Examples 15 to 33 containing particles in the range of 5% by volume or more and 40% by volume or less and containing third silver particles having a particle size of less than 50 nm in the range of 5% by volume or less. When the fired film was prepared, the bonding strength of the bonded body was as large as 38 MPa to 50 MPa, and the thermal diffusion rate of the silver fired film was as large as 122 W / mK to 155 W / mK.

<Comparative test 3 and evaluation>
For the bonded bodies of Examples 15 to 17 and Comparative Example 3, the cross section of the bonded layer was observed by FE-SEM. The results are shown in FIGS. 1 to 4.

As is clear from FIGS. 1 to 4, in the zygote prepared by using the silver paste of Comparative Example 3 (FIG. 4) to which no fatty acid silver was added, many deficiencies were present in the zygote layer. On the other hand, in the bonded body prepared by using the silver paste of Examples 15 to 17 (FIGS. 1 to 3) in which silver acetate was added as the fatty acid silver, the deficiency in the bonded layer was reduced. Further, in the conjugates of Examples 15 to 17, the content ratio of silver powder was increased from 75% by mass (Example 15: FIG. 1) to 80% by mass (Example 16: FIG. 2), and further increased to 85% by mass (Example 17). : It was found that the depletion in the junction layer decreased as the amount was increased to Fig. 3).

<Examples 34 and 35>
As the silver pastes of Examples 34 and 35, the types shown in Tables 1 and 6 were used as the mixed solution and the resin, and the silver powder, the mixed solution and the resin were mixed in the proportions shown in Table 6, respectively. The resin was added when the mixed solution and the silver powder were mixed, and kneaded together with these. A silver paste was prepared in the same manner as in Example 15 except for the formulations shown in Table 6.

<Comparative test 4 and evaluation>
Using the silver pastes of Examples 17, 34 and 35, joints were prepared in the same manner as in Comparative Test 2, and the joint strength of these joints was measured in the same manner as in Comparative Test 2. Further, using the silver pastes of Examples 17, 34 and 35, silver fired films were prepared in the same manner as in Comparative Test 2, and the thermal diffusivity of these silver fired films was set in the same manner as in Comparative Test 2. It was measured. Further, after performing a thermal cycle test on the joints of Examples 17, 34 and 35, the joint strength of these joints was measured in the same manner as in Comparative Test 2. The cold cycle test was carried out by repeating the operation of holding at −40 ° C. for 20 minutes and then holding at + 150 ° C. for 20 minutes using the vapor phase method for 1000 cycles. The results are shown in Tables 6 and 7.

In the resin type column in Table 6, "D1" indicates an epoxy-based thermosetting resin composition, and "D2" indicates a silicone-based thermosetting resin composition (both liquid and cured at room temperature). Temperature: 140-150 ° C). Further, in the column of the type of silver powder in Table 6, No. 1 is the silver powder of No. 1 in Table 5, and the mixed solution is the mixed solution of Example 1 in Table 1. Further, in Table 6, the blending ratio of the resin is the ratio when the silver paste is 100% by mass.

As is clear from Tables 6 and 7, when the bonded body and the silver fired film were prepared using the silver paste of Example 17 to which no resin was added, the initial bonding strength of the bonded body (before the thermal cycle test) was formed. Was as large as 50 MPa, and the thermal diffusivity of the silver fired film was as large as 150 W / mK, but the bonding strength of the bonded body after the cold cycle test was as small as 22 MPa. On the other hand, when a bonded body and a silver-fired film were prepared using the silver paste of Example 34 to which an epoxy-based thermosetting resin composition was added as a resin, the bonding strength at the initial stage of the bonded body (before the cold cycle test). Was 35 MPa, which was smaller than that of Example 17, and the thermal diffusivity of the silver-fired film was 100 W / mK, which was smaller than that of Example 17, but the bonding strength of the bonded body after the cold cycle test was 36 MPa, which was larger than that of Example 17. It was.

When a bonded body and a silver fired film were prepared using the silver paste of Example 35 to which a silicone-based thermosetting resin composition was added as the resin, the initial bonding strength of the bonded body (before the cold cycle test) was 25 MPa. The heat diffusion rate of the silver-fired film was 101 W / mK, which was smaller than that of Example 17, but the bonding strength of the bonded body after the cold cycle test was 23 MPa, which was larger than that of Example 17.

The silver paste of the present invention can be used as a bonding layer for bonding a circuit board and a high-power LED element, a bonding layer for bonding a circuit board and a power semiconductor chip, and the like.

The silver paste preferably further contains either one or both of the resin and the solvent. Examples of the resin include epoxy-based resins, silicone-based resins, acrylic-based resins, and mixtures thereof. Epoxy resins include bisphenol A type epoxy resins, novolak type epoxy resins, cyclic aliphatic epoxy resins, and mixtures thereof, and silicone resins include methyl silicone resins, epoxy modified silicone resins, and polyester modified silicones. There are resins and mixtures thereof, and acrylic resins include acrylate-based monomer resins and the like. These resins are cured by heating the silver paste, and the cured product is filled in the voids of the sintered body of silver powder . By filling the voids of the sintered body of silver powder with the cured product of the thermosetting resin composition, the mechanical strength of the bonding layer is improved, and the decrease in bonding strength under a thermal cycle load is suppressed. The content of the resin may be in the range of 0.1% by mass to 3% by mass when the whole silver paste is 100% by mass. If the content of the resin is less than 0.1% by mass, the mechanical strength of the bonding layer may not be improved, and if it exceeds 3% by mass, sintering of silver powder is hindered and the mechanical strength of the bonding layer is lowered. There is a risk. The content of the resin may be preferably in the range of 0.2% by mass to 2.5% by mass, and more preferably in the range of 0.3% by mass to 2.0% by mass. Good.

<Examples 16 to 33 and Comparative Examples 3 to 8>
As the silver pastes of Examples 16 to 33 and Comparative Examples 3 to 8, the fatty acid silver, aliphatic amines and solvent types shown in Table 1 were used as the mixed solution, and the silver powder and the mixed solution were used in Tables 3 and 4. The silver paste was prepared in the same manner as in Example 15 except for the formulations shown in Tables 3 and 4, respectively. The mixed solutions used in Examples 15 to 33 and Comparative Examples 3 to 8 are shown in any of Examples 1 to 14 in the column of mixed solution types in Tables 3 and 4. Further, in Examples 15 to 33 and Comparative Examples 3 to 8, any one of 10 types (No. 1 to No. 10) of silver powder having different particle size distributions shown in Table 5 is blended, and Examples 15 to 33 are blended. And the silver powder used in Comparative Examples 3 to 8 is shown by any of No. 1 to No. 10 in the column of the type of silver powder in Tables 3 and 4.

(2-1) Method for Measuring Thermal Diffusivity of Silver-Fired Film The thermal diffusivity of the silver-fired films of Examples 15 to 33 and Comparative Examples 3 to 8 was measured by a laser flash method. Specifically, first, the temperature change T (t) on the back surface of the silver fired film when the surface of the silver fired film was uniformly irradiated with a pulse laser and instantaneously heated was measured. Next, since the temperature change T (t) on the back surface of the silver fired film is expressed by a one-dimensional heat conduction equation, the temperature change T (t) on the back surface of the silver fired film is taken on the vertical axis and the elapsed time t is horizontal. By taking the axis, a (T (t) -t) curve was obtained, and the time t _0.5 required to reach half the maximum temperature rise temperature T _{MAX was} calculated from this curve. Then, the thermal diffusivity α of the silver fired film was obtained by the following equation (2).
α = 1.370 x L ² / (π ² x t _0.5 ) …… (2)
L in the formula (2) is the thickness of the silver fired film. Tables 3 and 4 show the bonding strength of these bonded bodies and the thermal diffusivity of the silver-fired film .

In the resin type column in Table 6, "D1" indicates an epoxy-based thermosetting resin composition, and "D2" indicates a silicone-based thermosetting resin composition (both liquid and cured at room temperature). Temperature: 140-150 ° C). Further, in the column of the type of silver powder in Table 6, No. 1 is the silver powder of No. 1 in Table 5, and the mixed solution is the mixed solution of Example 1 in Table 1. Further, in Table 6, the blending ratio of the resin is the ratio when the silver paste is 100% by mass.

A first aspect of the present invention is a silver paste containing silver powder, fatty acid silver, an aliphatic amine, and a solvent , wherein the silver powder contains first silver particles having a particle size of 100 nm or more and less than 500 nm . The second silver particles having a particle size of 50 nm or more and less than 100 nm and the third silver particles having a particle size of less than 50 nm are formed , and the total amount of the first to third silver particles is 100% by mass. The first silver particles are contained in the range of 55% by mass or more and 95% by mass or less, the second silver particles are contained in the range of 5% by mass or more and 40% by mass or less, the third silver particles are contained in the range of 5% by mass or less, and the fatty acid silver and the fat. When the total amount of the group amine and the solvent is 100% by mass, the fatty acid silver is 13.2% by mass to 33.0% by mass, the aliphatic amine is 0.1% by mass to 60% by mass, and the above. It is characterized in that the content of the silver powder is 50% by mass to 95% by mass when the solvent is contained in a proportion of 80% by mass or less and the silver paste is 100% by mass .

A third aspect of the present invention is an invention based on the first aspect, further comprising a complex formed by reacting at least a part of silver fatty acid and at least a part of an aliphatic amine. To do.

The fourth aspect of the present invention is that the fatty acid silver is 13.2 when the total amount of the fatty acid silver, the aliphatic amine and the solvent is 100% by mass. A step of mixing the aliphatic amine at a ratio of 0.1% by mass to 60% by mass and the solvent at a ratio of 80% by mass or less to obtain a mixture, and mixing the mixture at 30 ° C. to 100% by mass to 33.0 % by mass. A method for producing a silver paste, which comprises a step of heating to ° C., stirring, and then cooling to obtain a mixed solution, and a step of kneading the mixed solution and silver powder to obtain a silver paste. The silver powder is a grain. a first silver particle size less than 500nm or 100nm, the particle size is composed of a second silver particles is less than 100nm or 50 nm, and the third silver particles a particle size of less than 50 nm, and the first to With respect to the total amount of 3 silver particles of 100% by mass, the first silver particles are 55% by mass or more and 95% by mass or less, the second silver particles are 5% by mass or more and 40% by mass or less, and the third silver particles are 5 It is characterized in that the content of the silver powder is 50% by mass to 95% by mass when it is contained in the range of volume% or less and the silver paste is 100% by mass .

A fifth aspect of the present invention is the step of preparing the first member and the second member, and the silver according to any one of the first to third aspects on the surface of the first member and / or the second member. A step of applying a paste or a silver paste produced by the method according to claim 4 to form a silver paste layer, and laminating the first member and the second member via the silver paste layer to prepare a laminate. By heating the laminate, the first silver particles, the second silver particles, and the third silver particles in the silver paste layer are sintered to form a bonding layer, and the first member and the second member are formed. It is a method of manufacturing a bonded body including a step of producing a bonded body bonded via a bonded layer.

In the silver paste according to the first aspect of the present invention, the silver powder contains first silver particles having a particle size of 100 nm or more and less than 500 nm in a range of 55% by volume or more and 95% by volume or less, and the particle size is 50 nm or more and less than 100 nm. Since certain second silver particles are contained in the range of 5% by volume or more and 40% by volume or less and third silver particles having a particle size of less than 50 nm are contained in the range of 5% by volume or less, the silver powder has a relatively wide particle size distribution. By having the particles, the gaps between the first to third silver particles become small and dense during sintering, so that a bonding layer with few voids can be produced. Further, since the silver paste further contains a solvent, it is possible to obtain an excellent effect that the viscosity of the silver paste can be adjusted to facilitate operations such as coating.

Since the silver paste according to the third aspect of the present invention contains a complex formed by reacting at least a part of fatty acid silver and at least a part of an aliphatic amine, fine silver is precipitated from the complex at the time of firing. By filling the space between the first silver particles, the second silver particles, and the third silver particles in the silver paste, the bonded layer produced by using the silver paste becomes more dense and its heat. Conduction characteristics can be dramatically improved.

In the method for producing a silver paste according to the fourth aspect of the present invention, a mixed solution in which a mixture of fatty acid silver, an aliphatic amine and a solvent is mixed at a predetermined ratio is heated and stirred, and then cooled to prepare a mixed solution. And silver powder are kneaded to prepare a silver paste, and the silver powder contains first silver particles having a particle size of 100 nm or more and less than 500 nm in a range of 55% by volume or more and 95% by volume or less, and has a particle size of 50 nm or more and 100 nm. Since the second silver particles having a particle size of less than 50% by volume are contained in the range of 5% by volume or more and 40% by volume or less and the third silver particles having a particle size of less than 50 nm are contained in the range of 5% by volume or less, the silver powder is similarly described above. Since the particles have a relatively wide particle size distribution, the gaps between the first to third silver particles become small and dense during sintering, so that a bonding layer with few voids can be produced.

In the method for producing a bonded body according to the fifth aspect of the present invention, the first member and the second member are laminated with the silver paste layer coated with the silver paste sandwiched between them to prepare a laminated body, and the laminated body is formed. By heating, the first silver particles, the second silver particles, and the third silver particles in the silver paste layer are sintered to form a bonding layer, and the first member and the second member are bonded via the bonding layer. Since the bonded body is produced, the bonding layer for joining the bonded body has few voids, and the heat conduction characteristics and the cold cycle characteristics of the bonded body produced by this method can be improved.

A method for producing the silver paste thus constructed will be described. First, when fatty acid silver, aliphatic amine and solvent are prepared and the total amount of fatty acid silver, aliphatic amine and solvent is 100% by mass, for example, fatty acid silver is 13.2 % by mass to 33.0 % by mass. %, The aliphatic amine is mixed at a ratio of 0.1% by mass to 60% by mass, and the solvent is mixed at a ratio of 80% by mass or less. Here, the fatty acid silver, the mixing ratio of the aliphatic amine and a solvent is limited to within the range, without causing precipitation or the like to the mixture, based rather on grounds that an effect is obtained of the present invention.

Claims (6)

A silver paste containing silver powder, fatty acid silver, and an aliphatic amine.
The silver powder contains first silver particles having a particle size of 100 nm or more and less than 500 nm in a range of 55% by volume or more and 95% by volume or less, and 5% by volume or more of second silver particles having a particle size of 50 nm or more and less than 100 nm. A silver paste containing in the range of 5% by volume or less and containing third silver particles having a particle size of less than 50 nm in the range of 5% by volume or less. The silver paste according to claim 1, further comprising a resin. The silver paste according to claim 1, further comprising a solvent. The silver paste according to claim 1, which comprises a complex formed by reacting at least a part of the fatty acid silver with at least a part of the aliphatic amine. When the total amount of the fatty acid silver, the aliphatic amine and the solvent is 100% by mass, the fatty acid silver is 0.1% by mass to 40% by mass, and the fat. A step of mixing the group amine at a ratio of 0.1% by mass to 60% by mass and the solvent at a ratio of 80% by mass or less to obtain a mixture.
A step of heating the mixture to 30 ° C. to 100 ° C., stirring the mixture, and then cooling the mixture to obtain a mixed solution.
A method for producing a silver paste, which comprises a step of kneading the mixed solution and silver powder to obtain a silver paste.
The silver powder contains first silver particles having a particle size of 100 nm or more and less than 500 nm in a range of 55% by volume or more and 95% by volume or less, and 5% by volume or more of second silver particles having a particle size of 50 nm or more and less than 100 nm. A method for producing a silver paste, which comprises a third silver particle having a particle size of less than 50 nm in a volume of 5% by volume or less. The process of preparing the first member and the second member,
A silver paste layer is formed by applying the silver paste according to any one of claims 1 to 4 or the silver paste produced by the method according to claim 5 to the surface of the first member and / or the second member. And the process of forming
A step of laminating the first member and the second member via the silver paste layer to prepare a laminated body, and
By heating the laminate, the first silver particles, the second silver particles, and the third silver particles in the silver paste layer are sintered to form a bonding layer, and the first member and the second member are formed. A method for producing a bonded body, which comprises a step of producing a bonded body bonded via a bonded layer.