Mixed silver powder, method for producing same, and metal paste for bonding

Abstract

The purpose of the present invention is to provide a mixed silver powder capable of imparting high thermal conductivity to a metal bonding layer. The present invention is a mixed silver powder in which a particle size distribution obtained by wet-type measurement using a laser diffraction particle size distribution measurement device, wherein the vertical axis is the volume distribution proportion and the horizontal axis is the particle diameter, includes a first peak and a second peak where the volume distribution proportion is 1% or higher. The relationship between the particle diameter dM1 of the first peak and the particle diameter dM2 of the second peak satisfies formula (I): dM1 < dM2 and formula (II): 4.5 μm ≤ dM2 − dM1 ≤ 16.0 μm. The relationship between the volume distribution proportion A of whichever of the first peak and the second peak has the lower volume distribution proportion and the volume distribution proportion B, which is the minimum volume distribution proportion occurring between the first peak and the second peak, satisfies formula (III): 1.2 ≤ A / B or formula (IV): 0 = B / A.

Description

Mixed silver powder, its manufacturing method, and metal paste for joining

[0001] The present invention relates to a mixed silver powder, a method for producing the same, and a metal paste for bonding.

[0002] Traditionally, solder has been used as a joining material for joining components. However, due to the low melting point of solder, it has been difficult to use it for power device elements such as silicon carbide and gallium nitride, which have high operating temperatures. Therefore, metal paste containing highly heat-resistant metal nanoparticles is currently used as a joining material.

[0003] For example, Patent Document 1 discloses a metal bonding paste containing, as a paste component, a metal nanoparticle powder such as silver nanoparticles having an aggregate particle diameter of 1 μm or more. When this metal bonding paste is used to bond two members, a bonded body with high bonding strength can be obtained.

[0004] JP 2014-224296 A

[0005] Here, in bonding using a bonding metal paste, a metal bonding layer having high thermal conductivity is desired from the viewpoint of heat dissipation in the metal bonding layer.

[0006] Therefore, an object of the present invention is to provide a mixed silver powder capable of imparting high thermal conductivity to a metal bonding layer, a method for producing the same, and a metal bonding paste containing the mixed silver powder.

[0007] As a result of extensive research by the present inventors to solve the above-mentioned problems, the present inventors have completed the present invention described below.

[0008] That is, the gist and configuration of the present invention for solving the above-mentioned problems is as follows.

[0009] [1] In a particle size distribution obtained by wet measurement using a laser diffraction particle size distribution analyzer, the vertical axis represents the volume distribution ratio and the horizontal axis represents the particle diameter, and the particle size distribution includes a first peak and a second peak, the volume distribution ratio of which is 1% or more, and the particle diameter d of the first peak Ｍ１ and the particle diameter d of the second peak Ｍ２ The relationship between these is expressed by the following formula (I) and formula (II):Ｍ１ <d Ｍ２ ...(I) 4.5μm≦d Ｍ２ -d Ｍ１ ≦16.0 μm (II), and the relationship between a volume distribution ratio A of the peak having a smaller volume distribution ratio out of the first peak and the second peak and a volume distribution ratio B at which the volume distribution ratio between the first peak and the second peak is minimum satisfies the following formula (III) or formula (IV): 1.2≦A / B (III) 0=B / A (IV).

[0010] [2] The mixed silver powder according to [1], wherein more than 50% of the volume distribution ratio of the first peak is derived from spherical silver powder, and more than 50% of the volume distribution ratio of the second peak is derived from flaky silver powder.

[0011] [3] the above d Ｍ１ is 0.5 μm or more and 1.5 μm or less, Ｍ２ The mixed silver powder according to [1] or [2], wherein the particle size is 5.0 μm or more and 17.5 μm or less.

[0012] [4] The mixed silver powder according to any one of [1] to [3], wherein the ratio of ignition loss to BET specific surface area is 0.65 or less.

[0013] [5] Tap density is 3.5 g / cm ３ The mixed silver powder according to any one of [1] to [4] above.

[0014] [6] A method for producing a mixed silver powder, comprising a mixing step of mixing a first silver powder and a second silver powder, wherein the first silver powder and the second silver powder are respectively measured in a wet state using a laser diffraction particle size distribution analyzer, and in a particle size distribution where the vertical axis is the volume distribution ratio and the horizontal axis is the particle diameter, the particle diameter d of the peak of the maximum volume distribution ratio of the first silver powder is Ｓ１ and the particle diameter d of the second silver powder at the peak of the maximum volume distribution ratio. Ｓ２ The relationship between the formula (i) and the formula (ii) is as follows: Ｓ１ <d Ｓ２ ...(i) 4.6μm≦d Ｓ２ -d Ｓ１≦16.0 μm (ii), and the cumulative 94% diameter D of the first silver powder satisfies ９４ and the cumulative 6% diameter D of the second silver powder. ６ The relationship between these is expressed by the following formula (iii): D ９４ ≦D ６ A method for producing a mixed silver powder, which satisfies the above condition (iii).

[0015] [7] The method for producing a mixed silver powder according to [6], wherein the first silver powder is a spherical silver powder and the second silver powder is a flaky silver powder.

[0016] [8] The spherical silver powder has a cumulative 50% diameter D ５０ is 0.5 μm or more and 1.5 μm or less, and the tap density is 2.0 g / cm ３ or more, and the BET specific surface area is 0.6 m ２ / g or more 2.2m ２ / g or less, and the flaky silver powder has a cumulative 50% diameter D ５０ is 5.0 μm or more and 17.5 μm or less, and the tap density is 2.0 g / cm ３ or more, and the BET specific surface area is 0.2 m ２ / g or more 2.0m ２ / g or less and an aspect ratio of 3 or more.

[0017] [9] A metal bonding paste containing the mixed silver powder according to any one of [1] to [5].

[0018] According to the present invention, it is possible to provide a mixed silver powder capable of imparting high thermal conductivity to a metal bonding layer, a method for producing the same, and a metal bonding paste containing the mixed silver powder.

[0019] 1 is a schematic diagram illustrating a method for evaluating shear strength in the examples. 2 is a graph showing the particle size distribution of silver powder according to Example 1. 3 is a graph showing the particle size distribution of silver powder according to Example 2. 4 is a graph showing the particle size distribution of silver powder according to Example 3. 5 is a graph showing the particle size distribution of silver powder according to Example 4. 6 is a graph showing the particle size distribution of silver powder according to Example 5. 7 is an SEM photograph (2000x) of flaky silver powder A. 8 is an SEM photograph (2000x) of flaky silver powder B. 9 is an SEM photograph (2000x) of flaky silver powder C. 10 is an SEM photograph (2000x) of flaky silver powder D. 11 is an SEM photograph (2000x) of flaky silver powder E. 12 is an SEM photograph (2000x) of spherical silver powder A. 13 is an SEM photograph (2000x) of spherical silver powder A. 14 is an SEM photograph (2000x) of spherical silver powder B. 1 is an SEM photograph (2000x magnification) of silver powder according to Example 1. 2 is an SEM photograph (2000x magnification) of silver powder according to Example 2. 3 is an SEM photograph (2000x magnification) of silver powder according to Example 3. 4 is an SEM photograph (2000x magnification) of silver powder according to Example 4. 5 is an SEM photograph (2000x magnification) of silver powder according to Example 5. 6 is an SEM photograph (2000x magnification) of silver powder according to Comparative Example 4. 7 is an SEM photograph (2000x magnification) of silver powder according to Comparative Example 7. 8 is a graph showing the particle size distribution of silver powder according to Comparative Example 1. 9 is a graph showing the particle size distribution of silver powder according to Comparative Example 2. 10 is a graph showing the particle size distribution of silver powder according to Comparative Example 3. 11 is a graph showing the particle size distribution of silver powder according to Comparative Example 4. 12 is a graph showing the particle size distribution of silver powder according to Comparative Example 5. 10 is a graph showing the particle size distribution of the silver powder according to Comparative Example 6. FIG. 11 is a graph showing the particle size distribution of the silver powder according to Comparative Example 7.

[0020] (Terminology and Measurement Methods) First, prior to describing the embodiments, the terminology and measurement methods used in this specification will be described.

[0021] <Method for measuring particle size distribution> In this specification, the volume-based cumulative 6% particle diameter (D ６ ), cumulative 10% particle diameter (D １０ ), cumulative 50% particle diameter (D ５０ ), cumulative 90% particle diameter (D ９０ ), cumulative 94% particle diameter (D ９４The particle size distribution and its distribution were measured by the following method. 0.1 g of silver powder was added to 40 mL of isopropyl alcohol (IPA) and dispersed for 2 minutes using an ultrasonic homogenizer (apparatus name: US-150T, manufactured by Nippon Seiki Seisakusho Co., Ltd.; 19.5 kHz, tip diameter: 18 mm), and then wet measurement was performed using a laser diffraction particle size analyzer (Microtrac MT-3300 EXII, manufactured by Microtrac-Bell Corporation). For the silver powder (spherical silver powder A) of Comparative Example 2 described below, 0.1 g of silver powder was added to 40 mL of a 1 wt % polyvinylpyrrolidone (PVP) solution (solvent: isopropyl alcohol), and the resulting solution was dispersed for 2 minutes using an ultrasonic homogenizer. Measurements were performed using the above method in the present invention, and a graph of the particle size distribution, calculated on a volume basis, was obtained, with the vertical axis representing the volume distribution ratio (unit: %) and the horizontal axis representing the particle diameter (unit: μm). The particle size distribution graph is a histogram, and the volume distribution ratio is the cumulative value of particle volume in each particle size interval divided by the total volume of the measured particles. The particle size intervals on the horizontal axis were measured so that the ratio between the minimum particle diameters of adjacent intervals was 1.09. In this specification, the "peak" in the particle size distribution refers to the point where the particle diameter is minimum in the interval where the volume frequency distribution ratio is maximum. When identifying a peak, if adjacent intervals have the same volume distribution ratio, the interval with the smaller particle diameter is used.

[0022] <Ignition loss (Ig-loss) of silver powder> Ignition loss (Ig-loss) of silver powder was measured by weighing 2 g of silver powder sample (w １ ) and placed in a porcelain crucible, ignited at 800°C for 30 minutes, cooled, and weighed (w ２ ) by calculating "Ignition loss (%) = [(w １ -w ２ ) / w １ ]×100”.

[0023] <BET Specific Surface Area> Using a specific surface area measuring device employing the BET method (Macsorb HM-model 1210, manufactured by MOUNTECH), 3 g of silver powder was placed in a measurement cell, and a carrier gas mixture of 70 vol % He gas and 30 vol % nitrogen gas was passed through the measurement cell to perform degassing at 60°C for 10 minutes, after which the BET specific surface area was determined by the BET single-point method.

[0024] <Tap Density (TAP)> The tap density of silver powder is the apparent density of the silver powder in a container after a predetermined amount of silver powder is weighed and placed in a container of a predetermined capacity, and the container is dropped a predetermined number of times (hereinafter referred to as "after tapping"). The tap density was determined by dividing the weight of the silver powder in the container by the apparent volume of the silver powder in the container. Specifically, the tap density of the silver powder was determined by using a tap density measuring device (Shibayama Scientific Co., Ltd., bulk specific gravity measuring device SS-DA-2), weighing 30 g of silver powder, placing it in a container (20 mL test tube), tapping it 1,000 times at a drop of 20 mm, and dividing the weight of the silver powder (30 g) by the apparent volume (mL) of the silver powder after tapping. For the flaky silver powders B and C, and the silver powders according to Comparative Examples 4 and 5, which will be described later, the weight of the silver powder was set to 15 g, and the apparent volume (mL) of the silver powder after tapping was divided by the weight of the silver powder, to determine the apparent volume.

[0025] <Average aspect ratio> Here, when a uniform model of disc particles is used, the average aspect ratio is calculated as follows: "Average aspect ratio = D ５０ / t" (t means thickness). The thickness t (unit: μm) can be calculated by "t = D ５０ / ((ρ×(D ５０ / 2) × BET specific surface area) - 2) (ρ means the particle density). Therefore, in this specification, the average aspect ratio of silver powder can be calculated by the D ５０ and the BET specific surface area of ​​the silver powder, and the true density of the silver powder, 10.49 g / cm ３ Using this, "average aspect ratio = (10.49 x (D ５０ / 2) x BET) - 2.

[0026] <Spherical Silver Powder> In this specification, the term "spherical silver powder" refers to a shape that is close to a sphere and has an average aspect ratio of less than 2.

[0027] <Flake Silver Powder> In this specification, the term "flake silver powder" refers to silver powder having a shape with an average aspect ratio of 2 or more, including flat plates, thin rectangular parallelepipeds, flakes, and scales.

[0028] (Mixed Silver Powder) The mixed silver powder of the present invention has a particle size distribution (hereinafter sometimes simply referred to as "particle size distribution") obtained by wet measurement using a laser diffraction particle size distribution analyzer, in which the vertical axis represents the volume distribution ratio and the horizontal axis represents the particle diameter. The particle size distribution includes a first peak and a second peak, each having a volume distribution ratio of 1% or more, and the particle diameter d Ｍ１ and the particle diameter d of the second peak Ｍ２ The relationship between these is expressed by the following formula (I) and formula (II): Ｍ１ <d Ｍ２ ...(I) 4.5μm≦d Ｍ２ -d Ｍ１ Furthermore, the mixed silver powder of the present invention satisfies the second peak particle diameter d Ｍ２ and the particle diameter d of the first peak Ｍ１ The difference between (d Ｍ２ -d Ｍ１) is in the above-mentioned range, and the two peaks are separated by the above-mentioned range, so that at least one valley occurs between the first peak and the second peak in the particle size distribution of the mixed silver powder. In the mixed silver powder of the present invention, the relationship between the volume distribution ratio A of the peak with the smaller volume distribution ratio out of the first peak and the second peak and the volume distribution ratio B at the position where the volume distribution ratio of the valley between the first peak and the second peak is minimum satisfies the following formula (III) or formula (IV): 1.2≦A / B (III) 0=B / A (IV). Such a mixed silver powder can impart high thermal conductivity to the metal bonding layer. The reason for this is presumably that the silver particles with small particle size and high sinterability that form the first peak penetrate into the gaps between the silver particles with large particle size that form the second peak, thereby increasing the conductive paths between the silver particles with large particle size in the metal bonding layer, thereby achieving the effect of reducing the number of particles obtained by using large silver particles and the effect of increasing the contact surface area between the large silver particles. In addition, in the particle size distribution of the mixed silver powder, it is preferable that there are only two peaks with a volume distribution ratio of 1% or more, but if there are three or more peaks with a volume distribution ratio of 1% or more, the first peak and second peak refer to the two peaks with the largest volume distribution ratios.

[0029] In the particle size distribution of the mixed silver powder, the particle diameter d of the second peak Ｍ２ and the particle diameter d of the first peak Ｍ１ The difference between (d Ｍ２ -d Ｍ１ ) is 4.5 μm or more, preferably 6.0 μm or more, and is 16.0 μm or less, preferably 13.0 μm or less.

[0030] In the mixed silver powder of the present invention, the relationship between the volume distribution ratio A and the volume distribution ratio B is not particularly limited as long as it satisfies formula (III) or formula (IV), but it is preferable that formula (III) is satisfied. Here, in the particle size distribution of the mixed silver powder, the ratio of the volume distribution ratio A to the volume distribution ratio B (A / B) is 1.2 or more, and preferably 1.5 or more. On the other hand, the ratio of the volume distribution ratio A to the volume distribution ratio B (A / B) may be, for example, 1.5 or less, or may be 1.25 or less.

[0031] The volume distribution ratio A is not particularly limited as long as it satisfies the relationship of formula (III), but is preferably 1.0% or more, more preferably 1.6% or more, and is preferably 4.0% or less, more preferably 3.0% or less.

[0032] The volume distribution ratio B is not particularly limited as long as it satisfies the relationship of formula (III), but is preferably 0.5% or more, more preferably 0.7% or more, and is preferably 3.0% or less, more preferably 2.0% or less.

[0033] In the particle size distribution of the mixed silver powder, it is preferable that more than 50% of the volume distribution ratio of the first peak is derived from spherical silver powder, and more than 50% of the volume distribution ratio of the second peak is derived from flaky silver powder. If more than 50% of the volume distribution ratio of the first peak is derived from spherical silver powder and more than 50% of the volume distribution ratio of the second peak is derived from flaky silver powder, fine spherical silver particles with small particle diameters and high sinterability can easily enter the gaps between larger flaky silver particles, thereby increasing the conductive paths between larger flaky silver particles in the metal bonding layer, thereby achieving the effect of reducing the particle number of flaky silver powder and the effect of further increasing the contact area between flaky silver particles having flat surfaces. Preferably, 70% or more, more preferably 90% or more of the volume distribution ratio of the first peak is derived from spherical silver powder. Furthermore, it is more preferable that 100% of the volume distribution ratio of the first peak is derived from the spherical silver powder, i.e., that it is derived solely from the spherical silver powder. The volume distribution ratio of the second peak is preferably 70% or more, more preferably 90% or more, derived from the flaky silver powder. Furthermore, it is more preferable that 100% of the volume distribution ratio of the second peak is derived from the flaky silver powder, i.e., that it is derived solely from the flaky silver powder.

[0034] In the particle size distribution of the mixed silver powder, d Ｍ１ is 0.5 μm or more and 1.5 μm or less, and d Ｍ２ is preferably 5 μm or more and 17.5 μm or less. Ｍ１ and d Ｍ２Within the above range, it is possible to achieve both high sinterability due to the fine silver powder and the effect of reducing the number of particles due to the large silver powder and the effect of increasing the contact surface between the large silver particles. Ｍ１ is preferably 0.6 μm or more, more preferably 0.8 μm or more, and is preferably 1.4 μm or less, more preferably 1.3 μm or less. Ｍ２ is preferably 6.0 μm or more, more preferably 7.0 μm or more, and is preferably 16.0 μm or less, more preferably 11.0 μm or less.

[0035] Mixed silver powder D １０ is preferably 0.3 μm or more, more preferably 0.4 μm or more, and is preferably 1.5 μm or less, more preferably 1.2 μm or less. １０ If the D of the mixed silver powder is 0.3 μm or more, the fine silver particles having a small particle size can be densely inserted into the gaps between the large silver particles. １０ If the particle size is 1.5 μm or less, the good sinterability of small silver particles can be utilized.

[0036] Mixed silver powder D ５０ is preferably 1.0 μm or more, more preferably 1.1 μm or more, and is preferably 8.0 μm or less, more preferably 6.0 μm or less.

[0037] Mixed silver powder D ９０ is preferably 7.0 μm or more, more preferably 8.0 μm or more, and is preferably 20.0 μm or less, more preferably 17.0 μm or less. ９０ If the D of the mixed silver powder is 7.0 μm or more, it is possible to reduce the number of large silver particles in the metal bonding layer and increase the contact area between the silver particles. ９０ If the particle size is 20.0 μm or less, the gaps between the large particles are not too wide, and the silver particles having a small particle size can be densely packed in.

[0038] In the mixed silver powder, (D ９０ -D１０ ) / D ５０ is preferably 1.8 or more, more preferably 1.9 or more, and is preferably 10.0 or less, more preferably 7.2 or less. Within the above range, a certain number of fine silver powder particles with small particle diameters and silver powder particles with large particle diameters are mixed together, and the small silver particles can densely fill the gaps between the large particles, thereby improving the filling property of the metal bonding layer.

[0039] The tap density of the mixed silver powder is 3.5 g / cm ３ It is preferable that the density is 5.0 g / cm or more. ３ More preferably, it is 7.0 g / cm or more. ３ It is preferable that the density is 6.3 g / cm or less. ３ It is more preferable that the tap density of the mixed silver powder is 3.5 g / cm or less. ３ On the other hand, if the tap density of the mixed silver powder is 7.0 g / cm or more, the filling property of the metal bonding layer is improved. ３ If the filling rate is higher than this, the bonding material will be too hard and brittle, and there is a risk of cracks occurring due to warping caused by thermal stress or the like.

[0040] The BET specific surface area of ​​the mixed silver powder is 0.61 m ２ / g or more, and 0.65m ２ / g or more, and ２ / g or less, and ２ It is more preferable that the BET specific surface area of ​​the mixed silver powder is 0.61 m / g or less. ２ On the other hand, if the BET specific surface area of ​​the mixed silver powder is 1.40 m / g or more, a sufficient contact area between particles can be secured. ２ If the viscosity is 1 / g or less, the viscosity of the paste for forming the metal bonding layer can be maintained at a good level.

[0041] In the mixed silver powder, the ratio of ignition loss (Ig-loss) to BET specific surface area ("Ig-loss" / "BET specific surface area") is preferably 0.15 or more, more preferably 0.30 or more, and preferably 0.65 or less, more preferably 0.57 or less. When the "Ig-loss" / "BET specific surface area" of the mixed silver powder is 0.15 or more, the silver powder can be well dispersed. On the other hand, when the "Ig-loss" / "BET specific surface area" of the mixed silver powder is 0.65 or less, the amount of impurities between particles can be kept low, thereby reducing the resistance between particles after heating and improving the thermal conductivity of the metal bonding layer. Here, the ratio of ignition loss (Ig-loss) to BET specific surface area is the value of the ignition loss (Ig-loss) in the silver powder in mass% in units of m ２ / g, divided by the value of the BET specific surface area of ​​the silver powder. Note that, although the units of "Ig-loss" / "BET specific surface area" are omitted in this specification, the units are "mass% g / m ２ "

[0042] The mixed silver powder of the present invention is not particularly limited as long as it satisfies the relationships of formulas (I) to (IV), but it may also be a mixture containing a first silver powder and a second silver powder described below in a predetermined ratio.

[0043] (Method for producing mixed silver powder) The method for producing a mixed silver powder of the present invention (hereinafter, sometimes simply referred to as the "production method") includes a mixing step of mixing a first silver powder and a second silver powder, and the first silver powder and the second silver powder are each measured in a wet state using a laser diffraction particle size distribution analyzer. In the particle size distribution obtained, the vertical axis represents the volume distribution ratio and the horizontal axis represents the particle diameter, and the particle diameter d of the peak of the maximum volume distribution ratio of the first silver powder is calculated. Ｓ１ and the particle diameter d of the second silver powder at the peak of the maximum volume distribution ratio. Ｓ２ The relationship between the formula (i) and the formula (ii) is as follows: Ｓ１ <d Ｓ２ ...(i) 4.6μm≦d Ｓ２ -d Ｓ１ ≦16.0 μm (ii), and the cumulative 94% diameter D of the first silver powder satisfies ９４ and the cumulative 6% diameter D of the second silver powder６ The relationship between the D of silver powder and the D of silver powder is as follows: ９４ ≦D of silver powder ６ ...(iii). The above-described mixed silver powder can provide a metal bonding layer with high thermal conductivity. The above-described mixed silver powder of the present invention can be obtained by the manufacturing method of the present invention. The means for mixing the first silver powder and the second silver powder in the mixing step of the manufacturing method of the present invention is not particularly limited, and can be performed using a mixer such as a Henschel mixer or a sample mill.

[0044] In the particle size distributions of the first silver powder and the second silver powder, the particle diameter d of the peak of the maximum volume distribution ratio of the second silver powder Ｓ２ and the particle diameter d of the first silver powder at the peak of the maximum volume distribution ratio. Ｓ１ The difference between (d Ｓ２ -d Ｓ１ ) is 4.6 μm or more, preferably 6.0 μm or more, and is 16.0 μm or less, preferably 12.0 μm or less.

[0045] In the particle size distribution of the first silver powder and the second silver powder, the cumulative 6% diameter D of the second silver powder ６ and the cumulative 94% diameter D of the first silver powder ９４ The difference between ６ -D ９４ ) is preferably 0.0 μm or more, more preferably 0.1 μm or more, and is preferably 3.0 μm or less, more preferably 2.5 μm or less.

[0046] The mass ratio of the first silver powder to the total mass of the first silver powder and the second silver powder is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 90% by mass or less, and more preferably 80% by mass or less. If the mass ratio of the first silver powder to the total mass of the first silver powder and the second silver powder is within the above range, a certain number of fine silver powder with a small particle size and large flake silver powder are mixed, and the small silver particles can densely fill the gaps between the large particles, improving the filling of the metal bonding layer and allowing the effects of each silver powder to be exerted.

[0047] In the particle size distribution of the first silver powder, d Ｓ１ is preferably 0.4 μm or more, more preferably 0.7 μm or more, and is preferably 1.5 μm or less, more preferably 1.3 μm or less.

[0048] In the particle size distribution of the first silver powder, the volume distribution ratio of the peak of the maximum volume distribution ratio of the first silver powder is preferably 4.0% or more, more preferably 5.0% or more, and there is no particular upper limit.

[0049] The shape of the first silver powder is not particularly limited, but is preferably spherical, i.e., the first silver powder is preferably spherical silver powder.

[0050] First Silver Powder D １０ is preferably 0.1 μm or more, more preferably 0.2 μm or more, and is preferably 0.7 μm or less, more preferably 0.4 μm or less.

[0051] First Silver Powder D ５０ is preferably 0.5 μm or more, more preferably 0.6 μm or more, and is preferably 1.5 μm or less, more preferably 1.2 μm or less.

[0052] First Silver Powder D ９０ is preferably 0.8 μm or more, more preferably 1.2 μm or more, and is preferably 1.9 μm or less, more preferably 1.6 μm or less.

[0053] First Silver Powder D ９４ is preferably 0.9 μm or more, more preferably 1.3 μm or more, and is preferably 2.0 μm or less, more preferably 1.8 μm or less. １０ , D ５０ , D ９０ , D ９４ If the value of is within the above range, the sinterability will not deteriorate and the particles can densely enter the gaps between large particles.

[0054] The tap density of the first silver powder is 2.0 g / cm ３ It is preferable that the density is 3.5 g / cm or more. ３ More preferably, it is 7.0 g / cm or more. ３ Preferably, it is 6.0 g / cm or less. ３ It is more preferable that the tap density of the first silver powder is 2.0 g / cm or less. ３ On the other hand, if the tap density of the first silver powder is 7.0 g / cm or more, the filling property of the metal bonding layer can be improved. ３ If the filling rate is higher than this, the bonding material will be too hard and brittle, and there is a risk of cracks occurring due to warping caused by thermal stress or the like.

[0055] The BET specific surface area of ​​the first silver powder is 0.6 m ２ / g or more, and ２ / g or more, and ２ / g or less, and ２ / g or less. ２ On the other hand, if the BET specific surface area is 2.2 m / g or more, the sinterability can be improved. ２ If the content is 0.1g or less, the viscosity of the paste for forming the metal bonding layer containing the mixed silver powder can be maintained at a good level.

[0056] In the first silver powder, the ratio of ignition loss (Ig-loss) to BET specific surface area ("Ig-loss" / "BET specific surface area") is preferably 0.15 or more, more preferably 0.20 or more, and preferably 0.65 or less, more preferably 0.57 or less. If the "Ig-loss" / "BET specific surface area" of the first silver powder is 0.15 or more, the dispersibility of the silver powder can be improved. On the other hand, if the "Ig-loss" / "BET specific surface area" of the first silver powder is 0.65 or less, impurities between particles can be kept to a minimum, thereby reducing the resistance between particles after heating and improving the thermal conductivity of the metal bonding layer.

[0057] In the particle size distribution of the second silver powder, d Ｓ２is preferably 5.0 μm or more, more preferably 7.0 μm or more, and is preferably 17.5 μm or less, more preferably 16.0 μm or less.

[0058] In the particle size distribution of the second silver powder, the volume distribution ratio of the peak of the maximum volume distribution ratio of the second silver powder is preferably 4.0% or more, more preferably 5.0% or more, and there is no particular upper limit.

[0059] The shape of the second silver powder is not particularly limited, but is preferably flaky. That is, the first silver powder is preferably flaky silver powder. Here, when the second silver powder is flaky silver powder, the aspect ratio of the flaky silver powder is preferably 3 or more, more preferably 8 or more, and is preferably 40 or less, more preferably 30 or less. If the aspect ratio of the flaky silver powder is 3 or more, the flat portions of the individual silver particles are sufficiently present, and the contact area between the particles can be secured. On the other hand, if the aspect ratio of the flaky silver powder is 40 or less, good filling of the metal bonding layer can be secured.

[0060] Second Silver Powder D ６ is preferably 1.0 μm or more, more preferably 1.4 μm or more, and is preferably 5.0 μm or less, more preferably 4.0 μm or less.

[0061] Second Silver Powder D １０ is preferably 1.5 μm or more, more preferably 2.0 μm or more, and is preferably 7.0 μm or less, more preferably 5.0 μm or less.

[0062] Second Silver Powder D ５０ is preferably 5.0 μm or more, more preferably 6.0 μm or more, and is preferably 17.5 μm or less, more preferably 13.0 μm or less.

[0063] Second Silver Powder D ９０is preferably 8.0 μm or more, more preferably 12.0 μm or more, and is preferably 25.0 μm or less, more preferably 22.0 μm or less. ６ , D １０ , D ５０ , D ９０ If the amount of silver powder that is not flaked is within the above range, there is little unflaked silver powder and there is little excessively flaked particles, so that the mixture with the first silver powder is compatible and the filling property of the metal bonding layer can be improved.

[0064] The tap density of the second silver powder is 2.0 g / cm ３ It is preferable that the density is 4.0 g / cm or more. ３ More preferably, it is 7.0 g / cm or more. ３ Preferably, it is 6.5 g / cm or less. ３ It is more preferable that the tap density of the second silver powder is 2.0 g / cm or less. ３ If the tap density of the second silver powder is 7.0 g / cm or more, there will be few excessively flaked particles, and the filling property of the metal bonding layer can be improved. ３ If the particle size is less than this, there are enough flat surfaces of the particles, and the contact area between the particles can be secured.

[0065] The BET specific surface area of ​​the second silver powder is 0.2 m ２ / g or more, and 0.25m ２ / g or more, and ２ / g or less, and ２ It is more preferable that the BET specific surface area is 0.2 m / g or less. ２ / g or more, there are sufficient flat surfaces of the particles, and the contact area can be secured. ２ If the particle size is 1 / g or less, there are few excessively flaked particles or fine particles, and the effect of large flake silver powder can be improved.

[0066] In the second silver powder, the ratio of ignition loss (Ig-loss) to BET specific surface area ("Ig-loss" / "BET specific surface area") is preferably 0.15 or more, more preferably 0.20 or more, and preferably 0.65 or less, more preferably 0.57 or less. If the "Ig-loss" / "BET specific surface area" of the second silver powder is 0.15 or more, the dispersibility of the silver powder can be improved. On the other hand, if the "Ig-loss" / "BET specific surface area" of the second silver powder is 0.65 or less, impurities between particles can be kept to a minimum, thereby reducing the resistance between particles after heating and improving the thermal conductivity of the metal bonding layer.

[0067] In one embodiment, the first silver powder is preferably a spherical silver powder and the second silver powder is preferably a flaky silver powder. If the first silver powder is a spherical silver powder and the second silver powder is a flaky silver powder, the small spherical silver powder can be densely intercalated between the large flaky silver particles, thereby increasing the conductive paths between the large flaky silver particles in the metal bonding layer, thereby reducing the number of flaky silver powder particles and increasing the contact area between the flaky silver particles having flat surfaces.

[0068] In one embodiment, when the first silver powder is a spherical silver powder and the second silver powder is a flake silver powder, the spherical silver powder has a cumulative 50% diameter D ５０ is 0.5 μm or more and 1.5 μm or less, and the tap density is 2.0 g / cm ３ or more, and the BET specific surface area is 0.6 m ２ / g or more 2.2m ２ / g or less, and the flaky silver powder has a cumulative 50% diameter D ５０ is 5.0 μm or more and 17.5 μm or less or 16 μm or less, and the tap density is 2.0 g / cm ３ or more, and the BET specific surface area is 0.2 m ２ / g or more 2.0m ２ / g or less, and the aspect ratio is preferably 3 or more. If the spherical silver powder and flaky silver powder have the above properties, the fine spherical silver particles, which have a small particle size and high sinterability, can easily enter the gaps between the large flaky silver particles, thereby increasing the number of conductive paths between the large flaky silver particles in the metal bonding layer, thereby achieving the effect of reducing the number of flaky silver powder particles and the effect of increasing the contact area between the flat-surfaced flaky silver particles.

[0069] The first silver powder and the second silver powder are not particularly limited and can be produced by a conventionally known method.

[0070] (Metal Paste for Bonding) The metal paste for bonding of the present invention contains the mixed silver powder of the present invention described above. Because the metal paste for bonding of the present invention contains the mixed silver powder of the present invention, it can impart high thermal conductivity to the metal bonding layer. The metal paste for bonding typically contains a solvent. The solvent is not particularly limited, and examples thereof include water, monoalcohols, polyols, ether compounds, glycol ether acetates, nitrogen-containing cyclic compounds, and ester compounds. Examples of monoalcohols include 1-octanol, terpineol, texanol, phenoxypropanol, 1-decanol, 1-dodecanol, 1-tetradecanol, Tersolve MTPH (manufactured by Nippon Terpene Chemical Co., Ltd.), dihydroterpinyloxyethanol (manufactured by Nippon Terpene Chemical Co., Ltd.), Tersolve TOE-100 (manufactured by Nippon Terpene Chemical Co., Ltd.), and Tersolve DTO-210 (manufactured by Nippon Terpene Chemical Co., Ltd.). Examples of polyols include 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol (octanediol), hexyl diglycol, 2-ethylhexyl glycol, dibutyl diglycol, glycerin, dihydroxyterpineol, 3-methylbutane-1,2,3-triol (isoprene triol A (IPTL-A), manufactured by Nippon Terpene Chemical Co., Ltd.), and 2-methylbutane-1,2,4-triol (isoprene triol B (IPTL-B), manufactured by Nippon Terpene Chemical Co., Ltd.). Examples of ether compounds include butyl carbitol, diethylene glycol monobutyl ether, terpinyl methyl ether (manufactured by Nippon Terpene Chemical Co., Ltd.), and dihydroterpinyl methyl ether (manufactured by Nippon Terpene Chemical Co., Ltd.). Examples of glycol ether acetates include butyl carbitol acetate, diethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, etc. Examples of nitrogen-containing cyclic compounds include 1-methylpyrrolidinone, pyridine, etc.Examples of ester compounds include γ-butyrolactone, methoxybutyl acetate, methoxypropyl acetate, ethyl lactate, 3-hydroxy-3-methylbutyl acetate, dihydroterpinyl acetate, Tersolve IPG-2Ac (manufactured by Nippon Terpene Chemical Co., Ltd.), Tersolve THA-90 (manufactured by Nippon Terpene Chemical Co., Ltd.), and Tersolve THA-70 (manufactured by Nippon Terpene Chemical Co., Ltd.). The solvents listed above may be used alone or in combination of two or more.

[0071] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples. The BET specific surface area, particle size distribution, ignition loss (Ig-loss), tap density, and average aspect ratio were measured or calculated by the methods described above.

[0072] (Preparation of Flake Silver Powder A) First, 167.1 kg of a 26 wt % aqueous ammonia solution was added to 2,922 kg of a silver nitrate aqueous solution containing 68.8 kg of silver as a silver ion aqueous solution to produce a silver ammine complex aqueous solution. Furthermore, 266 kg of a 6 wt % aqueous hydrazine solution as a reducing agent was added to this silver ammine complex aqueous solution to obtain a first liquid. The reducing agent was added at a rate of 80 L / min. The first liquid was in the form of a slurry containing silver particles. The first liquid was filtered, washed with water, and then dried to obtain a pre-silver powder. This pre-silver powder was composed of aggregates of uniformly sized silver particles. 15.5 kg of the pre-silver powder was added to a Henschel mixer (Mitsui Mining Co., Ltd., FM mixer, Model FM75, using an SO-type agitating blade) and stirred at 900 rpm for 1 minute. Then, 49.6 g of palmitic acid (0.32 wt % based on the weight of the pre-silver powder (calculated as 49.6 g of palmitic acid / 15,500 g of pre-silver powder x 100)) was added as a lubricant, and the mixture was mixed and stirred for 20 minutes at a blade rotation speed of 2,600 rpm (lubricant mixing step). This step was performed in multiple batches to obtain a lubricant-treated silver powder in which the lubricant was dispersed on the surfaces of the silver particles. 31 kg of the obtained lubricant-treated silver powder was placed in a tumbling ball mill with an inner diameter of 60 cm and a length of 40 cm, together with 313.2 kg of SUS balls (diameter 1.6 mm), and flaking treatment was carried out at a rotation speed of 21 rpm for 7 hours. The balls and flaked silver powder after the treatment were separated using a vibrating sieve. 30 kg of the flaked silver powder was added to approximately 35 L of neoethanol adjusted to 28°C or higher, stirred for 30 minutes, and then subjected to solid-liquid separation using a pressure filter and dried. 14 kg of the dried flaked silver powder was added to a Henschel mixer (Mitsui Mining Co., Ltd., FM mixer, model FM75, using SO-type stirring blades), stirred at 900 rpm for 1 minute, and then crushed at 2600 rpm for 15 minutes. Furthermore, to remove coarse particles from the crushed silver powder, it was sieved using a dry sieving device (Freund Turbo Corporation, TS125x200 type / 24 μm mesh screen) to obtain flaked silver powder A. The results of various measurements of flaked silver powder A are shown in Table 1. FIG. 7 shows an SEM photograph (2000x magnification) of the flaky silver powder A.

[0073] (Preparation of Flake Silver Powder B) FA-S-10 manufactured by DOWA Electronics was prepared as Flake Silver Powder B. The results of various measurements on Flake Silver Powder B are shown in Table 1. Also, an SEM photograph (2000x magnification) of Flake Silver Powder B is shown in Figure 8.

[0074] (Preparation of Flake Silver Powder C) FA-S-18 manufactured by DOWA Electronics was prepared as Flake Silver Powder C. The results of various measurements on Flake Silver Powder C are shown in Table 1. Also, an SEM photograph (2000x magnification) of Flake Silver Powder C is shown in Figure 9.

[0075] (Preparation of Flake Silver Powder D) First, 167.1 kg of a 26 wt% aqueous ammonia solution was added to 2,922 kg of a silver nitrate solution containing 68.8 kg of silver as a silver ion solution to produce a silver ammine complex solution. Furthermore, 266 kg of a 6 wt% aqueous hydrazine solution as a reducing agent was added to this silver ammine complex solution to obtain a first solution. The reducing agent was added at a rate of 80 L / min. The first solution was in the form of a slurry containing silver particles. Five minutes after the completion of the reducing agent addition, 68.8 g of oleic acid (0.1 wt% of the weight of silver contained in the silver ammine complex solution (calculated as 68.8 g oleic acid / 68,800 g silver x 100)) was added as a surface treatment agent. After the addition of the surface treatment agent, the mixture was stirred for five minutes to obtain a second solution. The second solution was in the form of a slurry. The second solution was filtered, washed with water, and then dried to obtain a pre-silver powder. This pre-silver powder was composed of aggregates of uniformly sized silver particles. 16.25 kg of the above pre-silver powder was charged into a Henschel mixer (manufactured by Mitsui Mining Co., Ltd., FM mixer, model FM75, using SO-type stirring blades) and stirred at 900 rpm for 1 minute, after which 37.4 g of oleic acid (0.23 wt % based on the weight of the pre-silver powder (calculated as 37.4 g oleic acid / 16,250 g pre-silver powder x 100)) was charged as a lubricant, and the mixture was mixed and stirred for 20 minutes at a stirring blade speed of 2,600 rpm (lubricant mixing step). This step was performed in multiple batches to obtain lubricant-treated silver powder in which the lubricant was dispersed on the surfaces of the silver particles. 32 kg of the above lubricant-treated silver powder and 256 kg of SUS balls (diameter 1.6 mm) were charged into a vibration mill (Chuo Kakoki Co., Ltd., FVR-20 model) and flaked for 135 minutes at a vibration frequency of 780 vpm to obtain flaked silver powder. After separating the SUS balls, the flaked silver powder was pulverized by stirring at 2600 rpm for 25 minutes in the above Henschel mixer. Furthermore, to remove coarse particles from the pulverized silver powder, it was sieved using a dry sieving device (Freund Turbo Corporation, TS125x200 model / 27 μm screen) to obtain flaked silver powder D (pulverized silver powder after sieving). The results of various measurements of flaked silver powder D are shown in Table 1. FIG. 10 shows an SEM photograph (2000x magnification) of flaky silver powder D.

[0076] (Preparation of Flake-Shaped Silver Powder E) 122.1 kg of 26.28 wt% aqueous ammonia was added to 2,411 kg of an aqueous silver nitrate solution containing 64.8 kg of silver to produce a silver ammine complex solution. 6 kg of a 31.15 wt% aqueous sodium hydroxide solution was then added to the resulting aqueous silver ammine complex solution, followed by 158.4 kg of a 37 wt% aqueous formalin solution as a reducing agent. After the addition of the reducing agent was complete, 360 g of Cellosol 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt% stearic acid) was added as a surface treatment agent (0.56 wt% relative to the weight of silver contained in the aqueous silver ammine complex solution (0.09 wt% in terms of stearic acid)) to produce a slurry containing pre-silver powder. The second liquid was filtered, washed with water, and then dried to obtain pre-silver powder. This pre-silver powder was composed of aggregates of uniformly sized silver particles. 32.2 kg of the pre-silver powder was weighed and placed in a Henschel mixer (Mitsui Mining Co., Ltd., FM mixer, Model FM75, using an SO-type impeller). The impeller was rotated at 1,200 rpm for 1 minute to disintegrate the mixture. Then, 64.4 g (0.2 wt % based on the weight of the pre-silver powder) of stearic acid was added as a lubricant, and the mixture was further stirred at 1,200 rpm for 20 minutes. This resulted in a lubricant-treated silver powder in which the lubricant was dispersed on the surfaces of the silver particles. 32 kg of the lubricant-treated silver powder and 256 kg of SUS balls (diameter 1.6 mm) were placed in a vibration mill (Chuo Kakoki Co., Ltd., Model FVR-20) and flaked at a vibration frequency of 1,442 vpm for 60 minutes to flaking the lubricant-treated silver powder. Furthermore, to remove coarse particles, the sieve was sieved using a dry sieving device (manufactured by Freund Turbo Corporation, TS125x200 model / screen with 27 μm mesh size) to obtain flaked silver powder E (silver powder that had been sieved into flakes). The results of various measurements on flaked silver powder E are shown in Table 1. Also, an SEM photograph (2000x magnification) of flaked silver powder E is shown in FIG. 11.

[0077] (Preparation of Spherical Silver Powder A) 157.46 g of 28% by weight industrial ammonia water was added to 3618.2 g of a silver nitrate aqueous solution containing 51.78 g of silver to obtain a silver ammine complex aqueous solution. 9.60 g of a 20% by weight sodium hydroxide aqueous solution was added to this silver ammine complex aqueous solution, and the liquid temperature was adjusted to 25°C. After that, 140.42 g of a 7.3% by weight hydrazine aqueous solution was added as a reducing agent while stirring to obtain a slurry containing silver particles. 5.93 g of a 3.54% by weight oleic acid ethanol solution was added to the resulting silver particle-containing slurry and stirred. Stirring was stopped to allow the silver particles to settle, and the liquid containing the precipitated silver particles was filtered, washed with water until the electrical conductivity of the liquid after passing through the water was 0.5 mS / m or less, and then vacuum dried at 73°C. The silver powder obtained by repeating the above steps three times was milled twice for 90 seconds using a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) with 120 g of silver powder charged, to obtain spherical silver powder A. The results of various measurements on spherical silver powder A are shown in Table 1. Fig. 12 shows an SEM photograph (2000x magnification) of spherical silver powder A, and Fig. 13 shows an SEM photograph (20000x magnification) of spherical silver powder A.

[0078] (Preparation of Spherical Silver Powder B) 128.2 g of 28% by weight industrial ammonia water was added to 3790.3 g of a silver nitrate aqueous solution containing 58.91 g of silver to obtain a silver ammine complex aqueous solution. 9.43 g of an 80% by weight nitric acid aqueous solution was added to this silver ammine complex aqueous solution, followed by 0.619 g of a 5% by weight polyethyleneimine 600 (PEI600) aqueous solution. The liquid temperature was adjusted to 35°C, and then 338.0 g of a 2.5% by weight hydrazine aqueous solution was added as a reducing agent while stirring to obtain a silver particle-containing slurry. 4.94 g of a 1.55% by weight stearic acid emulsion solution was added to the resulting silver particle-containing slurry and stirred. Stirring was stopped to allow the silver particles to settle, and the liquid containing the precipitated silver particles was filtered, washed with water until the electrical conductivity of the liquid after passing through the water was 0.5 mS / m or less, and then vacuum dried at 73°C. The silver powder obtained by repeating the above steps three times was milled twice for 90 seconds using a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) with 120 g of silver powder charged, to obtain spherical silver powder B. The results of various measurements on spherical silver powder B are shown in Table 1. Also, an SEM photograph (2000x magnification) of spherical silver powder B is shown in Figure 14.

[0079]

[0080] Example 1 Spherical silver powder A corresponding to the first silver powder and flaky silver powder A corresponding to the second silver powder were charged into a Henschel mixer (manufactured by Mitsui Mining Co., Ltd., FM mixer, model FM75, using SO-type stirring blades) in a mass ratio of 50:50 (first silver powder:second silver powder) to a total weight of 24.8 kg, and mixed and stirred at 900 rpm for 1 minute and at 1500 rpm for 25 minutes. After that, in order to remove coarse particles, the mixture was sieved with a dry sieving device (manufactured by Freund Turbo Corporation, model TS125x200 / screen with 33 μm openings), thereby obtaining a silver powder (mixed silver powder) according to Example 1. Note that the d of flaky silver powder A corresponding to the second silver powder was Ｓ２ and d of spherical silver powder A corresponding to the first silver powder. Ｓ１ The difference between (d Ｓ２ -d Ｓ１ ) is 7.7 μm. Details of the first silver powder, the second silver powder, etc. are shown in Table 2. Various measurements were carried out using the silver powder of Example 1. The results are shown in Table 3. Furthermore, FIG. 2 shows the particle size distribution of the silver powder of Example 1, and FIG. 15 shows an SEM photograph (2000x magnification) of the silver powder of Example 1.

[0081] (Thermal Conductivity) <Formation of Evaluation Film> 27.9 g of the silver powder according to Example 1 and 2.1 g of 1-octanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a solvent were placed in a 30 mL plastic bottle and kneaded four times for 30 seconds at a revolution speed of 1,400 rpm using a propellerless rotary-revolving stirring and degassing device (manufactured by EME Corporation, V-mini300). This evaluation film-forming paste was applied to an alumina substrate using a 50 μm thick, 10.5 mm x 10.5 mm metal mask and a squeegee to form a coating film. The coated alumina substrate was placed in a firing furnace and fired without pressure to form an evaluation film. Pressureless firing was performed in a nitrogen atmosphere by heating the temperature to 250°C at 3.75°C / min, and then maintaining the temperature at 250°C for 1 hour.

[0082] <Measurement of Thickness of Evaluation Film> The average thickness of each of the obtained evaluation films was measured by measuring the difference in level between the portion of the alumina substrate on which no film was printed and the portion on which the evaluation film was printed using a surface roughness meter (SURFCOM 480B-12, manufactured by Tokyo Seimitsu Co., Ltd.).

[0083] <Measurement of Thermal Conductivity of Evaluation Films> The volume resistivity of each of the obtained evaluation films was measured at room temperature of 25°C using a four-probe measuring device (Loresta-GX MCP-T700, manufactured by Mitsubishi Chemical Analytech Co., Ltd.), and the thermal conductivity was calculated from the volume resistivity and temperature using the Wiedemann-Franz law. The results are shown in Table 3. The Wiedemann-Franz law is expressed by the following formula: K / σ=LT (1) In formula (1), K represents the thermal conductivity [W / K m], σ represents the electrical conductivity [S / m], and L represents the Lorentz number (2.44×10 －８ [WΩ / K ２ ]), and T represents the temperature [K]. The electrical conductivity σ can be calculated by "1 / ρ", and ρ represents the volume resistivity [Ω·m].

[0084] (Bonding Strength) <Preparation of Bonding Layer for Evaluation> A copper plate measuring 10 mm x 10 mm x 1 mm was degreased with ethanol and then treated with 10% sulfuric acid, and a Si chip measuring 2 mm x 2 mm x 0.3 mm with an Au back electrode was prepared. Next, a 50 μm thick metal mask was placed on the copper plate, and the above-mentioned bonding metal paste was printed in a size of 2 mm x 2 mm. Next, the Si chip was placed on the bonding material applied to the copper plate, and the thickness between the bonding material and the Si chip was adjusted to 13 μm. Next, the temperature was raised from 25 ° C. to 250 ° C. at a heating rate of 3.75 ° C. / min in a nitrogen atmosphere in a baking furnace, and the main baking was performed by holding at 250 ° C. for 60 minutes, sintering the silver in the silver paste to form a silver bonding layer, and the Si chip was bonded to the copper plate by this silver bonding layer.

[0085] <Shear Strength Evaluation> Using a bond tester SERIES4000Plus (manufactured by Nordson Dage), the shear strength of the test specimen obtained above was measured as shown in Figure 1. Specifically, the test specimen consisted of a copper substrate 3, a silver bonding layer 2 formed thereon, and a Si element 1 formed thereon and bonded to the copper substrate 3 via the silver bonding layer 2. A force was applied horizontally to the copper substrate 3 from the side of the Si element 1 using a shear tool 4 set at 5 mm / min. The force at break was divided by the area of ​​the bottom surface of the Si element to determine the shear strength of the test specimen, which was used as the bonding strength of the silver bonding layer. The above test was performed so that the lower end of the shear tool 4 abutted against a position 50 μm above the copper substrate 3. Bond strength was evaluated for Example 1 and Comparative Examples 1 and 2 (described below) as representative examples. The results are shown in Table 3.

[0086] Example 2 A silver powder (mixed silver powder) according to Example 2 was obtained in the same manner as in Example 1, except that the mass ratio of the first silver powder to the second silver powder was changed to 30:70 (first silver powder:second silver powder). Details of the first silver powder, second silver powder, etc. are shown in Table 2. Various measurements and evaluations were carried out using the silver powder according to Example 2. The results are shown in Table 3. FIG. 3 shows the particle size distribution of the silver powder according to Example 2, and FIG. 16 shows an SEM photograph (2000x magnification) of the silver powder according to Example 2.

[0087] Example 3 Spherical silver powder A corresponding to the first silver powder and flaky silver powder A corresponding to the second silver powder were mixed and stirred for 1.5 minutes in a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) in a mass ratio of 70:30 (first silver powder:second silver powder) to a total weight of 120 g, and then sieved with a 40 μm mesh to remove coarse particles, thereby obtaining a silver powder (mixed silver powder) according to Example 3. Details of the first silver powder and second silver powder are shown in Table 2. Various measurements and evaluations were carried out using the silver powder according to Example 3. The results are shown in Table 3. FIG. 4 shows the particle size distribution of the silver powder according to Example 3, and FIG. 17 shows an SEM photograph (2000x magnification) of the silver powder according to Example 3.

[0088] Example 4 A silver powder (mixed silver powder) according to Example 4 was obtained in the same manner as in Example 3, except that the mass ratio of the first silver powder to the second silver powder was changed to 20:80 (first silver powder:second silver powder). Details of the first silver powder, second silver powder, etc. are shown in Table 2. Various measurements and evaluations were carried out using the silver powder according to Example 4. The results are shown in Table 3. FIG. 5 shows the particle size distribution of the silver powder according to Example 4, and FIG. 18 shows an SEM photograph (2000x magnification) of the silver powder according to Example 4.

[0089] Example 5 A silver powder (mixed silver powder) according to Example 5 was obtained in the same manner as in Example 3, except that the mass ratio of the first silver powder to the second silver powder was changed to 80:20 (first silver powder:second silver powder). Details of the first silver powder, second silver powder, etc. are shown in Table 2. Various measurements and evaluations were carried out using the silver powder according to Example 5. The results are shown in Table 3. FIG. 6 shows the particle size distribution of the silver powder according to Example 5, and FIG. 19 shows an SEM photograph (2000x magnification) of the silver powder according to Example 5.

[0090] (Comparative Example 1) Various measurements and evaluations were carried out using only flaky silver powder A. Details of the first silver powder, second silver powder, etc. are shown in Table 2, and the results of the various measurements and evaluations are shown in Table 3. In addition, Fig. 24 shows the particle size distribution of the silver powder according to Comparative Example 1.

[0091] (Comparative Example 2) Various measurements and evaluations were carried out using only flaky silver powder B. Details of the first silver powder and second silver powder are shown in Table 2, and the results of the various measurements and evaluations are shown in Table 3. In addition, Fig. 25 shows the particle size distribution of the silver powder according to Comparative Example 2.

[0092] (Comparative Example 3) Various measurements and evaluations were carried out using only spherical silver powder A. Details of the first silver powder and second silver powder are shown in Table 2, and the results of the various measurements and evaluations are shown in Table 3. In addition, Fig. 26 shows the particle size distribution of the silver powder according to Comparative Example 3.

[0093] (Comparative Example 4) Spherical silver powder A corresponding to the first silver powder and flaky silver powder B corresponding to the second silver powder were mixed and stirred for 40 seconds in a coffee mill (Melitta Japan Co., Ltd., Melitta Electric Coffee Mill ECG-62) in a mass ratio of 20:80 (first silver powder:second silver powder) to a total weight of 50 g, to obtain a silver powder (mixed silver powder) according to Comparative Example 4. Note that the d of flaky silver powder B corresponding to the second silver powder was Ｓ２ and d of spherical silver powder A corresponding to the first silver powder. Ｓ１ The difference between (d Ｓ２ -d Ｓ１ ) is 2.2 μm. Details of the first silver powder, second silver powder, etc. are shown in Table 2. Various measurements and evaluations were carried out using the silver powder of Comparative Example 4. The results are shown in Table 3. FIG. 20 shows an SEM photograph (2000x magnification) of the silver powder of Comparative Example 4, and FIG. 27 shows the particle size distribution of the silver powder of Comparative Example 4.

[0094] (Comparative Example 5) Spherical silver powder A corresponding to the first silver powder and flaky silver powder C corresponding to the second silver powder were mixed and stirred for 40 seconds in a coffee mill (Melitta Japan Co., Ltd., Melitta Electric Coffee Mill ECG-62) in a mass ratio of 30:70 (first silver powder:second silver powder) to a total weight of 50 g, to obtain a silver powder (mixed silver powder) according to Comparative Example 5. Note that the d of flaky silver powder C corresponding to the second silver powder was Ｓ２ and d of spherical silver powder A corresponding to the first silver powder. Ｓ１ The difference between (d Ｓ２ -d Ｓ１ ) is 4.2 μm. Details of the first silver powder, second silver powder, etc. are shown in Table 2. Various measurements and evaluations were carried out using the silver powder of Comparative Example 5. The results are shown in Table 3. FIG. 21 shows an SEM photograph (2000x magnification) of the silver powder of Comparative Example 5, and FIG. 28 shows the particle size distribution of the silver powder of Comparative Example 5.

[0095] (Comparative Example 6) Spherical silver powder B corresponding to the first silver powder and flaky silver powder D corresponding to the second silver powder were mixed and stirred for 1.5 minutes in a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) in a mass ratio of 30:70 (first silver powder:second silver powder) to a total weight of 120 g, and then sieved with a 40 μm mesh to remove coarse particles, thereby obtaining a silver powder (mixed silver powder) according to Comparative Example 6. Note that the d of flaky silver powder D corresponding to the second silver powder wasＳ２ and d of spherical silver powder B corresponding to the first silver powder. Ｓ１ The difference between (d Ｓ２ -d Ｓ１ ) is 0.0 μm. Details of the first silver powder, second silver powder, etc. are shown in Table 2. Various measurements and evaluations were carried out using the silver powder of Comparative Example 6. The results are shown in Table 3. FIG. 22 shows an SEM photograph (2000x magnification) of the silver powder of Comparative Example 6, and FIG. 29 shows the particle size distribution of the silver powder of Comparative Example 6.

[0096] (Comparative Example 7) Spherical silver powder B corresponding to the first silver powder and flaky silver powder E corresponding to the second silver powder were mixed and stirred for 1.5 minutes in a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) in a mass ratio of 30:70 (first silver powder:second silver powder) to a total weight of 120 g, and then sieved with a 40 μm mesh to remove coarse particles, thereby obtaining a silver powder (mixed silver powder) according to Comparative Example 6. Note that the d of flaky silver powder E corresponding to the second silver powder was Ｓ２ and d of spherical silver powder B corresponding to silver powder I. Ｓ１ The difference between (d Ｓ２ -d Ｓ１ ) is 0.9 μm. Details of the first silver powder, second silver powder, etc. are shown in Table 2. Various measurements and evaluations were carried out using the silver powder of Comparative Example 6. The results are shown in Table 3. FIG. 23 shows an SEM photograph (2000x magnification) of the silver powder of Comparative Example 7, and FIG. 30 shows the particle size distribution of the silver powder of Comparative Example 7.

[0097]

[0098]

[0099] As is clear from Table 3, the particle size distribution includes a first peak and a second peak, the volume distribution ratio of which is 1% or more, and the particle diameter d Ｍ１ and the particle diameter d of the second peak Ｍ２ The relationship between these is expressed by the following formula (I) and formula (II): Ｍ１ <d Ｍ２ ...(I) 4.5μm≦d Ｍ２ -d Ｍ１≦16.0 μm (II), and the relationship between the volume distribution ratio A of the peak having the smaller volume distribution ratio out of the first peak and the second peak and the volume distribution ratio B at which the volume distribution ratio between the first peak and the second peak is smallest satisfies the following formula (III) or formula (IV): 1.2≦A / B (III) 0=B / A (IV), which shows that the silver powders (mixed silver powders) of Examples 1 to 5 can impart high thermal conductivity to the metal bonding layer.

[0100] As is clear from Table 3, in a method for producing a mixed silver powder including a mixing step of mixing a first silver powder and a second silver powder, the particle diameter d of the peak of the volume distribution ratio of the first silver powder, which is the largest in the particle size distribution of the first silver powder and the second silver powder, is Ｓ１ and the particle diameter d of the second silver powder at the peak of the maximum volume distribution ratio. Ｓ２ The relationship between the formula (i) and the formula (ii) is as follows: Ｓ１ <d Ｓ２ ...(i) 4.6μm≦d Ｓ２ -d Ｓ１ ≦16.0 μm (ii), and the cumulative 94% diameter D of the first silver powder satisfies ９４ and the cumulative 6% diameter D of the second silver powder ６ The relationship between these is expressed by the following formula (iii): D ９４ <D ６ It can be seen that the manufacturing methods of Examples 1 to 5, which satisfy the condition (iii), can obtain mixed silver powders that can impart high thermal conductivity to the metal bonding layer.

[0101] According to the present invention, it is possible to provide a mixed silver powder capable of imparting high thermal conductivity to a metal bonding layer, a method for producing the same, and a metal bonding paste containing the mixed silver powder.

[0102] REFERENCE SIGNS LIST 1 Si element 2 Silver bonding layer 3 Substrate 4 Shear tool

Claims

1. In the particle size distribution where the vertical axis is the volume distribution ratio (percentage) and the horizontal axis is the particle diameter, obtained by wet measurement using a laser diffraction particle size distribution measuring device, including a first peak and a second peak where the volume distribution ratio is 1% or more, the particle diameter d Ｍ１ of the first peak and the particle diameter d Ｍ２ of the second peak satisfy the following formulas (I) and (II): d Ｍ１ < d Ｍ２ ... (I) 4.5 μm ≤ d Ｍ２ − d Ｍ１ ≤ 16.0 μm... (II), and among the first peak and the second peak, the relationship between the volume distribution ratio A of the peak with the smaller volume distribution ratio and the volume distribution ratio B which is the minimum of the volume distribution ratios between the first peak and the second peak satisfies the following formula (III) or formula (IV): 1.2 ≤ A / B... (III) 0 = B / A... (IV). A mixed silver powder.

2. The mixed silver powder according to claim 1, wherein more than 50% of the volume distribution ratio of the first peak is derived from spherical silver powder, and more than 50% of the volume distribution ratio of the second peak is derived from flaky silver powder.

3. The d Ｍ１ is 0.5 μm or more and 1.5 μm or less, and the d Ｍ２ is 5.0 μm or more and 17.5 μm or less. The mixed silver powder according to claim 1.

4. The mixed silver powder according to claim 1, wherein the ratio of the loss on ignition to the BET specific surface area is 0.65 or less.

5. The tap density is 3.5 g / cm ３ or more, and the mixed silver powder according to claim 1.

6. A method for manufacturing mixed silver powder, comprising a mixing step of mixing first silver powder and second silver powder, wherein the first silver powder and the second silver powder are each measured wet by a laser diffraction particle size distribution measuring device, and in the particle size distribution with the vertical axis being the volume distribution ratio and the horizontal axis being the particle diameter, the particle diameter d of the peak of the maximum volume distribution ratio of the first silver powder Ｓ１ and the particle diameter d of the peak of the maximum volume distribution ratio of the second silver powder Ｓ２ satisfy the following formulas (i) and (ii): d Ｓ１ < d Ｓ２ ... (i) 4.6 μm ≤ d Ｓ２ − d Ｓ１ ≤ 16.0 μm... (ii), and the relationship between the cumulative 94% diameter D of the first silver powder ９４ and the cumulative 6% diameter D of the second silver powder ６ satisfies the following formula (iii): D ９４ ≤ D ６ ... (iii). A method for manufacturing mixed silver powder 7. The method for producing a mixed silver powder according to claim 6, wherein the first silver powder is spherical silver powder and the second silver powder is flaky silver powder.

8. The spherical silver powder has a cumulative 50% diameter D ５０ of 0.5 μm or more and 1.5 μm or less, a tap density of 2.0 g / cm ３ or more, and a BET specific surface area of 0.6 m ２ / g or more and 2.2 m ２ / g or less. The flaky silver powder has a cumulative 50% diameter D ５０ of 5.0 μm or more and 17.5 μm or less, a tap density of 2.0 g / cm ３ or more, a BET specific surface area of 0.2 m ２ / g or more and 2.0 m ２ / g or less, and an aspect ratio of 3 or more. The method for producing a mixed silver powder according to claim 7 9. A metal paste for bonding, comprising the mixed silver powder according to any one of claims 1 to 5.

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