JP2022003161A - Joining material, joining-material producing method, and joining method - Google Patents

Abstract

To provide a joining material including a coarse, metallic larger-particulate powder functioning as a spacer, and is less apt to cause cracking in a metal junction layer upon carrying out joining.SOLUTION: A joining material includes a metallic smaller-particulate powder having an average primary particle diameter equal to or smaller than 150 nm, a metallic larger particulate powder having a volume-based cumulative 90% particle diameter (D90) of 7-40 μm as measured by a laser-diffractive particle-size distribution measuring instrument, a compound A having a plurality of functional groups and a molecular weight of 600-1500, and a solvent.SELECTED DRAWING: Figure 2

Description

The present invention relates to a joining material, a method for manufacturing the joining material, and a joining method.

In recent years, in the field of power devices such as power LEDs, high-frequency devices, and inverters, the problem of heat generation of devices has become more serious with the miniaturization and higher output of devices, and the discussion of thermal management has become active. It's coming. Further, in other semiconductor devices as well, studies on changing from conventional silicon-based devices to compound semiconductor devices are progressing, and the junction temperature tends to increase.

Based on these technical backgrounds, heat dissipation and bonding reliability are required for materials for bonding various semiconductor devices and substrates. Recently, a bonding material using metal fine particle powder such as sintered silver has been attracting attention as a material that can realize this heat dissipation property and bonding reliability. Further, since such a bonding material is sintered at a low temperature to form a metal bonding layer, attention is also paid to the fact that a substrate having low heat resistance can be used.

As a joining method using a joining material containing metal fine particle powder, a method of applying the joining material to a substrate, placing a member to be joined on a coating film, and pressure sintering to form a metal joining layer is typical. Known as a traditional method. Here, if the formed metal bonding layer is thin, the bonding layer has a low stress relaxation capacity, and the bonding reliability (for example, the bonding strength, heat dissipation, and conductivity do not substantially change even after undergoing a thermal cycle). That) is insufficient.

To deal with such inconvenience, Patent Document 1 proposes a bonding material containing conductive particles obtained by coating resin particles having an average particle diameter of, for example, about 10 μm with silver, copper, or the like, and metal fine particles. Due to the presence of conductive particles that are much larger than the metal fine particles, the thickness of the metal bonding layer formed from such a bonding material corresponds to the size of the conductive particles. That is, the conductive particles function as a spacer that increases the thickness of the metal bonding layer (compared to the thickness of the metal bonding layer formed from the bonding material containing only metal fine particles as metal particles).

Patent Document 2 discloses a silver paste containing three types of silver particles. In the examples of Patent Document 2, these three types of silver particles are prepared or prepared in Production Examples 1 to 3, respectively.
It is described that the average particle size of the silver particles according to Production Example 1 is about 60 nm.
LM1 (manufactured by Toxen Industries, Ltd.) described as single crystal silver particles according to Production Example 2 is described as having a particle diameter of 0.1 to 5.0 μm, but D50 in the product catalog of the LM1 is 1.0. It is ± 0.3 μm.
AgC239 (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) described as non-spherical silver particles (flakes) according to Production Example 3 has a particle diameter of 2 to 15 μm, but the median diameter in the product catalog of AgC239. Is 2.0 to 3.4 μm.

Japanese Unexamined Patent Publication No. 2016-195126 Japanese Unexamined Patent Publication No. 2016-54098

The technique disclosed in Patent Document 2 has an object to provide a silver paste capable of forming a highly dense silver sintered body even when sintered at a low temperature and low pressure, and for this purpose, there are three sizes. By mixing different silver particles, fine silver particles are efficiently filled in the gaps formed by the large silver particles coming into contact with each other, and as a result, a silver sintered body having a high density is to be obtained. Among the silver particles used in the examples, even the largest one has a median diameter (cumulative 50% particle diameter) of about 3 μm, and the thickness of the silver sintered body (silver bonding layer) is about this size. Cannot be made large enough in terms of bonding reliability.

On the other hand, Patent Document 1 uses predetermined conductive particles as a spacer to form a thick metal bonding layer, but the core particles of the conductive particles are resin, which is the heat dissipation of the metal bonding layer. And has an adverse effect on conductivity.

As a result of diligent studies to solve such problems, the applicant of the present application filed an application for a bonding material containing a metal small particle powder and a coarse metal large particle powder that functions as a spacer. Request 2019-174120).

However, the present inventor has found that the above new configuration also has further problems. Specifically, when two bonded members such as a substrate and a semiconductor element are bonded using a bonding material containing coarse metal large particle powder according to the above application, cracks are formed in the metal bonding layer formed. May occur. The cracked metal bonding layer is concerned about deterioration of bonding reliability and deterioration of conductivity.

Therefore, it is an object of the present invention to provide a bonding material containing coarse metal large particle powder that functions as a spacer, and that is less likely to cause cracks in the metal bonding layer when bonding is performed.

[1] Small metal particle powder having an average primary particle diameter of 150 nm or less, large metal particle powder having a cumulative 90% particle diameter (D90) of 7 to 40 μm on a volume basis measured by a laser diffraction type particle size distribution measuring device, and a plurality of particles. A bonding material containing compound A having a functional group and a molecular weight of 600 to 1500, and a solvent.

[2] The small metal particle powder is composed of silver, copper, gold, aluminum or an alloy of two or more of these.
The bonding material according to [1], wherein the large metal particle powder is composed of silver, copper, gold, aluminum, or an alloy of two or more of these.

[3] The bonding material according to [1] or [2], wherein the cumulative 90% particle diameter (D90) of the large metal particle powder is 18 to 35 μm.

[4] The bonding material according to any one of [1] to [3], wherein the functional group is a hydroxyl group, an amino group, a thiol group or a carboxyl group.

（式（Ｉ）において、ｖ及びｙはそれぞれ独立に１〜２の整数であり、ｗは０〜１０の整数であり、ｘは１４〜４０の整数である。
式（ＩＩ）において、Ｒ^１は水素原子、カルボキシル基、ヒドロキシル基、アルコキシル基又は炭素数１〜１０のアルキル基を含む有機基である。ｐは１〜２０の整数、ｍは１〜５の整数である。ｍが２以上の場合、複数存在するＲ^１は互いに同一でも異なっていてもよく、複数存在する−（ＣＨ_２）_ｐ−は互いに同一でも異なっていてもよい。） [5] The bonding material according to any one of [1] to [4], wherein the compound A is a compound represented by the following formula (I) or (II):

(In the formula (I), v and y are independently integers of 1 to 2, w is an integer of 0 to 10, and x is an integer of 14 to 40.
In formula (II), R ¹ is an organic group containing a hydrogen atom, a carboxyl group, a hydroxyl group, an alkoxyl group or an alkyl group having 1 to 10 carbon atoms. p is an integer of 1 to 20, and m is an integer of 1 to 5. When m is 2 or more, a plurality of R ^1s may be the same or different from each other, and a plurality of − (CH ₂ ) _p − may be the same or different from each other. )

[6] The bonding material according to any one of [1] to [5], wherein the content of the small metal particle powder in the bonding material is 7 to 55% by mass.

[7] Of [1] to [6], further containing particle powder in a metal having a cumulative 50% particle diameter (D50) of 1.1 to 4.5 μm on a volume basis measured by a laser diffraction type particle size distribution measuring device. The bonding material described in either.

[8] The bonding material according to [7], wherein the content of the particle powder in the metal in the bonding material is 40 to 85% by mass.

[9] The bonding material according to any one of [1] to [8], wherein the content of the large metal particle powder in the bonding material is 2 to 20% by mass.

[10] The bonding material according to any one of [1] to [9], wherein the small metal particle powder is composed of silver and the large metal particle powder is composed of silver.

[11] The bonding material according to any one of [1] to [10], wherein the metal large particle powder has an average aspect ratio of 3 or less.

[12] Small metal particle powder having an average primary particle diameter of 150 nm or less, large metal particle powder having a cumulative 90% particle diameter (D90) of 7 to 40 μm based on a volume measured by a laser diffraction type particle size distribution measuring device, and a plurality of particles. A method for producing a bonding material, which comprises mixing a compound A having a functional group and a molecular weight of 600 to 1500 and a solvent.

[13] The small metal particle powder is composed of silver, copper, gold, aluminum or an alloy of two or more of these.
The method for producing a bonding material according to [12], wherein the large metal particle powder is composed of silver, copper, gold, aluminum or an alloy thereof.

[14] The amounts of the metal small particle powder and the metal large particle powder used, and the contents of the metal small particle powder and the metal large particle powder in the bonding material are 7 to 55% by mass and 2 to 20, respectively. The method for producing a bonding material according to [12] or [13], which is an amount that becomes a mass%.

（式（Ｉ）において、ｖ及びｙはそれぞれ独立に１〜２の整数であり、ｗは０〜１０の整数であり、ｘは１４〜４０の整数である。
式（ＩＩ）において、Ｒ^１は水素原子、カルボキシル基、ヒドロキシル基、アルコキシル基又は炭素数１〜１０のアルキル基を含む有機基である。ｐは１〜２０の整数、ｍは１〜５の整数である。ｍが２以上の場合、複数存在するＲ^１は互いに同一でも異なっていてもよく、複数存在する−（ＣＨ_２）_ｐ−は互いに同一でも異なっていてもよい。） [15] The method for producing a bonding material according to any one of [12] to [14], wherein the compound A is a compound represented by the following formula (I) or (II):

(In the formula (I), v and y are independently integers of 1 to 2, w is an integer of 0 to 10, and x is an integer of 14 to 40.
In formula (II), R ¹ is an organic group containing a hydrogen atom, a carboxyl group, a hydroxyl group, an alkoxyl group or an alkyl group having 1 to 10 carbon atoms. p is an integer of 1 to 20, and m is an integer of 1 to 5. When m is 2 or more, a plurality of R ^1s may be the same or different from each other, and a plurality of − (CH ₂ ) _p − may be the same or different from each other. )

[16] In addition to the small metal particle powder, large metal particle powder, compound A and a solvent, the cumulative 50% particle diameter (D50) on a volume basis measured by a laser diffraction type particle size distribution measuring device is 1.1 to 4 The method for producing a bonding material according to any one of [12] to [15], wherein 5 μm of the particle powder in the metal is mixed.

[17] The method for producing a bonding material according to [16], wherein the amount of the particle powder in the metal used is such that the content of the particle powder in the metal in the bonding material is 40 to 85% by mass.

[18] A joining method for joining two members to be joined.
The joining material according to any one of [1] to [11] or the joining material manufactured by the method for manufacturing a joining material according to any one of [12] to [17] is applied onto one of the members to be joined. And the process of forming a coating film
The step of placing the other member to be joined on the coating film, and
A bonding method comprising a step of firing a coating film on which the other member to be bonded is placed at 160 to 350 ° C. to form a metal bonding layer from the coating film.

[19] The joining method according to [18], wherein one of the members to be joined is a substrate and the other member to be joined is a semiconductor element.

According to the present invention, there is provided a bonding material containing coarse metal large particle powder that functions as a spacer, which is less likely to cause cracks in the metal bonding layer when bonding is performed.

FIG. 1 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Example 1 with a microfocus X-ray fluoroscope. be. FIG. 2 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Example 2 with a microfocus X-ray fluoroscope. be. FIG. 3 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Example 3 with a microfocus X-ray fluoroscope. be. FIG. 4 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Comparative Example 1 with a microfocus X-ray fluoroscope. be. FIG. 5 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Comparative Example 2 with a microfocus X-ray fluoroscope. be. FIG. 6 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Comparative Example 3 with a microfocus X-ray fluoroscope. be. FIG. 7 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Comparative Example 4 with a microfocus X-ray fluoroscope. be. FIG. 8 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Comparative Example 5 with a microfocus X-ray fluoroscope. be. FIG. 9 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Comparative Example 6 with a microfocus X-ray fluoroscope. be. FIG. 10 is a diagram showing the results of photographing the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding material of Comparative Example 7 with a microfocus X-ray fluoroscope. be.

Hereinafter, a joining material of the present invention, a method for manufacturing the joining material, and an embodiment of the joining method will be described.

[Joint material]
<Small metal particle powder>
Embodiments of the bonding material of the present invention include small metal particle powder having an average primary particle diameter of 150 nm or less. A powder of such a size is excellent in sinterability (hereinafter, also referred to as “low temperature sinterability”) by firing at a low temperature (for example, a temperature of 160 to 350 ° C.). From the viewpoint of low-temperature sinterability, the average primary particle diameter of the small metal particle powder is preferably 130 nm or less, more preferably 100 nm or less. The average primary particle diameter of the small metal particle powder is usually 1 nm or more.

In the present specification, the average primary particle size is an average value of the primary particle size (average primary particle based on the number) obtained from a transmission electron micrograph (TEM image) or a scanning electron micrograph (SEM image) of the particles. Diameter). More specifically, the particles are predetermined by, for example, a transmission electron microscope (TEM) (JEM-1011 manufactured by Nippon Denshi Co., Ltd.) or a scanning electron microscope (SEM) (S-4700 manufactured by Hitachi High-Technologies Co., Ltd.). Average primary particles from the primary particle diameter (diameter of a circle (area equivalent circle) having the same area as the particles) of 100 or more, preferably 250 arbitrary particles on the image (SEM image or TEM image) observed at the magnification of The diameter can be calculated. The diameter of the circle corresponding to the area can be calculated by, for example, image analysis software (A image-kun (registered trademark) manufactured by Asahi Kasei Engineering Co., Ltd.).

The content of the small metal particle powder in the embodiment of the bonding material of the present invention is from the viewpoint that the bonding material is sufficiently sintered by firing to form a strong metal bonding layer, and the bonding material of the large metal particle powder described later. From the viewpoint of ensuring the content in the metal and forming a thick metal bonding layer with few cracks, the content is preferably 7 to 55% by mass, more preferably 10 to 50% by mass.

The shape of the small metal particle powder is not particularly limited. It may have any shape such as substantially spherical (average aspect ratio of 1 to 1.5 described later), flakes, and amorphous, but substantially spherical metal small particle powder is preferable because it is easy to produce.

As the constituent metal of the small metal particle powder, silver, copper, gold and aluminum are preferable from the viewpoint of heat dissipation and conductivity. Of these, alloys of two or more kinds of metals may be used. From the same viewpoint and the viewpoint of cost, silver is particularly preferable as the constituent metal of the small metal particle powder.

Since the small metal particle powder has a small particle size, it tends to aggregate easily. In order to prevent this, it is preferable that the small metal particle powder is coated with an organic compound. As the organic compound, a known organic compound capable of covering the particle surface of the small metal particle powder can be used without particular limitation. Examples of the organic compound include organic compounds having 1 to 18 carbon atoms having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a thiol group and a disulfide group. The organic compound may have branches and may be saturated or unsaturated.

The organic compound preferably has 12 or less carbon atoms so that it is sufficiently separated from the small metal particle powder by firing at about 160 to 350 ° C. and does not hinder the sintering of the particles of the small metal particle powder. Saturated fatty acids or unsaturated fatty acids of number 2-8, saturated amines or unsaturated amines are more preferable. Examples of such fatty acids and amines include caproic acid, sorbic acid, hexylamine and octylamine.

The amount of the organic compound in the small metal particle powder is 0.1 to 12 mass out of 100% by mass of the small metal particle powder (including the organic compound covering the particles) from the viewpoint of preventing aggregation and low-temperature sinterability. %, More preferably 0.4 to 8% by mass. In the present specification, the amount of the organic compound in the small metal particle powder is obtained by raising the temperature of the small metal particle powder from room temperature to 700 ° C. and holding at 700 ° C. for 10 minutes to remove the organic compound. The rate of mass reduction at the time ((mass before heating-mass after heating) / mass before heating × 100 (mass%)). The same applies to the large metal particle powder and the medium particle powder described later.

<Metallic large particle powder>
An embodiment of the bonding material of the present invention comprises a large metal particle powder having a cumulative 90% particle size (D90) of 7 to 40 μm on a volume basis as measured by a laser diffraction type particle size distribution measuring device.

By including the powder of such large particles in the bonding material, it is possible to form a metal bonding layer according to the size while maintaining low temperature sinterability (due to the small metal particle powder). That is, the large metal particle powder functions as spacer particles that increase the thickness of the metal bonding layer.

The cumulative 90% particle size (D90) of the large metal particle powder is preferably 10 to 38 μm, more preferably 18 to 35 μm. In particular, when the D90 of the large metal particle powder is 18 μm or more, the metal bonding layer becomes thick and cracks are likely to occur, but by applying the present invention, the generation of cracks is suppressed.

It should be noted that the cumulative 90% particle diameter (D90) is defined in the particle size distribution according to the study of the present inventor, instead of the particle diameter generally called the average particle diameter such as the cumulative 50% particle diameter (D50). This is because it was found that the size of the particles per D90, which is a large region, but not the maximum size, is approximately reflected in the thickness of the metal bonding layer formed from the bonding material containing the large metal particle powder. That is, the thickness of the metal bonding layer corresponds to the size (D90) of one particle constituting the large metal particle powder, and the thickness of the metal bonding layer can be easily adjusted by the size of the particles of the large metal particle powder. Can be adjusted.

If the cumulative 99% particle diameter (D99) of the large metal particle powder is too large, the coating film formed by applying the bonding material on one of the members to be bonded, such as a substrate, has particles corresponding to D99. Only the coating film is thick, and when the other member to be bonded such as a semiconductor element is placed on it and fired to form a metal bonding layer, the other bonded member is formed in the vicinity of a portion of the particles. There is a possibility that a gap may be created between the member and the metal bonding layer, or the two members to be bonded cannot be bonded in parallel. From the viewpoint of avoiding such a situation, D99 is preferably 15 to 70 μm, more preferably 20 to 65 μm.

It is preferable that the particle size distribution of the large metal particle powder is narrow because it leads to a small number of small particles that do not function as a spacer. From this point, the cumulative 50% particle diameter (D50) of the large metal particle powder is preferably 5 to 30 μm, more preferably 6 to 28 μm, and even more preferably 7 to 25 μm.

Regarding the function as a spacer, the average aspect ratio of the large metal particle powder is preferably 3 or less, more preferably 1 to 2, still more preferably 1 to 1.5, and particularly preferably 1 to 1. It is 3. When the average aspect ratio is large, in the coating film formed by applying the bonding material on a member to be bonded such as a substrate, the constituent particles of the large metal particle powder have a line corresponding to the major axis perpendicular to the substrate. Unless the particles of the large metal particle powder are arranged in a direction close to (that is, each particle of the large metal particle powder is arranged vertically), the thickness of the metal bonding layer cannot be increased (the thickness of the metal bonding layer is the minor axis of the large metal particle powder). It will correspond to). However, it is difficult to assume that most of the constituent particles of the large metal particle powder having a large average aspect ratio are arranged in this way in the coating film. From the above, the preferable value of the average aspect ratio of the large metal particle powder is defined as described above.

The average aspect ratio of the large metal particle powder is the average value obtained by dividing the major axis of the constituent particles of the large metal particle powder by the minor axis, and the aspect ratio is individually obtained for any 100 or more arbitrary particles, and the average thereof is obtained. Calculated as a value. The major axis and the minor axis are the major axis and the minor axis in the planar shape of each constituent particle, which can be seen in the image obtained by observing the large metal particle powder by SEM at a predetermined magnification. In the image, first determine the major axis (the length of the longest line segment (major axis) that connects two points on the contour of the particle and does not pass outside the particle), and then The minor axis is the length of a line segment (minor axis) that connects two points on the contour of a particle that passes through the midpoint of the major axis and is orthogonal to the major axis and does not pass outside the particle. .. The average aspect ratio of the above-mentioned small metal particle powder and the medium-sized metal particle powder described later can also be calculated in the same manner as in the case of the large metal particle powder.

The content of the large metal particle powder in the embodiment of the bonding material of the present invention is preferably 2% by mass or more in order to sufficiently function as a spacer. Further, in addition to the function as a spacer, the content of the large metal particle powder in the bonding material is 2 to 20 from the viewpoint of securing the amount of the small metal particle powder in the bonding material to form a strong metal bonding layer. It is preferably by mass, more preferably 5 to 15% by mass.

The constituent metals of the large metal particle powder are the same as those of the small metal particle powder, and silver, copper, gold, and aluminum are preferable from the viewpoint of heat dissipation and conductivity. Of these, alloys of two or more kinds of metals may be used. As the constituent metal, silver is particularly preferable from the viewpoint of heat dissipation, conductivity and cost. From the viewpoint of forming a metal bonding layer having the same linear expansion coefficient as the metal small particle powder and having excellent bonding reliability, the metal small particle powder and the metal large particle powder are made of the same metal or alloy. Is preferable.

The large metal particle powder may be coated with an organic compound from the viewpoint of enhancing the dispersibility in the bonding material and enabling dense filling with the small metal particle powder. As the organic compound, a known organic compound capable of covering the particle surface of a large metal particle powder can be used without particular limitation. Examples of the organic compound include organic compounds having 12 to 24 carbon atoms having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a thiol group and a disulfide group. The organic compound may have branches and may be saturated or unsaturated. Examples of such organic compounds include lauric acid, myristic acid, margaric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, myristoleic acid, palmitic acid and the like.

The amount of the organic compound in the large metal particle powder is 0.05 to 1.5% by mass based on 100% by mass of the large metal particle powder (including the organic compound covering the particles) from the viewpoint of dispersibility. It is preferably 0.08 to 1.0% by mass, and more preferably 0.08 to 1.0% by mass.

<Compound A>
Embodiments of the bonding material of the present invention include compound A having a plurality of functional groups and having a molecular weight of 600 to 1500. More specifically, the embodiment of the bonding material of the present invention is a bonding material in which compound A is blended in addition to a small metal particle powder, a large metal particle powder, and a solvent described later.

It is considered that the compound A crosslinks various particles in the bonding material with its functional group to maintain a certain distance from each other so that the particles are evenly present in the bonding material. In this state, it is considered that the bonding material is applied to one of the members to be bonded such as a substrate to form a coating film, and the above state is maintained even if the coating film is formed. The molecular weight of compound A is in the above range and is not an excessively large value. Therefore, when the coating film is fired, the compound A volatilizes or decomposes and is separated from the coating film, and the particles (particularly small particles) are sufficiently sintered. As a result, it is considered that a bonding material in which cracks are less likely to occur in the metal bonding layer can be obtained when the bonding is performed.

Incidentally, when the compound A is not blended, it is considered that the particles are aggregated and settled and separated in the bonding material, and the particles are unevenly present in the bonding material. In other words, it is considered that the place where the particles are densely present and the place where the particles are sparsely exist coexist. It is considered that this state can occur even with a coating film. When the coating film is fired in this state, the place where the particles are sparsely present becomes a void, which is considered to be a crack in the metal bonding layer (when sedimentation separation occurs, the particle is substantially absent). The metal bonding layer is not formed in the place where only the organic component is present). In the metal small particle powder which is very small and easily aggregates, the constituent particles are preferably coated with an organic compound as described above in order to prevent aggregation. However, especially when the amount of the organic compound is in the above-mentioned preferable range, it is considered that the entire surface of the particles cannot be covered with the organic compound, and it is difficult to completely prevent aggregation. Therefore, it is considered that if compound A is not added to the bonding material as described above, particle agglutination will occur (and when compound A is added, the functional groups thereof will be bound to the surface of the particles not covered with the organic compound. Therefore, it is considered that the distance between the particles is maintained while preventing the aggregation of the particles).

The number of the plurality of functional groups in the compound A is not limited as long as it is 2 or more (the number of functional groups is preferably 2 to 16). Further, the type of functional group is not limited as long as it can exhibit the function of cross-linking various particles in the bonding material, maintaining a certain distance from each other, and allowing the particles to be evenly present in the bonding material. Specific examples thereof include a hydroxyl group, an amino group, a thiol group and a carboxyl group. The functional group contained in the compound A may be one kind or two or more kinds among them. A hydroxyl group, an amino group and a carboxyl group are preferable as the functional group from the viewpoint of minimizing the adverse effect on the semiconductor device.

From the viewpoint of exerting the above-mentioned function, it is preferable that the functional group is attached to the end of the main chain or side chain of compound A. The main chain is a chain composed of a divalent or higher atom (excluding divalent or higher atoms constituting the functional group) in compound A having the largest number of constituent atoms. Say. The side chain is a chain branched from any of the constituent atoms of the main chain (having one or more divalent or higher atoms (excluding divalent or higher atoms constituting the functional group)).

The molecular weight of the compound A is 600 or more as described above, and if the molecular weight is large as described above, the particles in the bonding material (and the coating film formed from the coating film) can maintain a certain distance from each other. On the other hand, the molecular weight of compound A is 1500 or less, and if the molecular weight is not too large as described above, the particles in the bonding material (and the coating film formed from the coating film) are present in a state of being too far apart from each other, so that the metal bonding layer is formed. It is possible to prevent the generation of cracks in the film (as described above, the compound A volatilizes / decomposes by firing, which also prevents the generation of cracks).

Regarding the molecular weight of compound A, when compound A is a mixture of compounds having different molecular weights such as a polymer, the average molecular weight may be defined as the molecular weight. In that case, the molecular weight of compound A refers to the weight average molecular weight Mw. The molecular weight of compound A is preferably 650 to 1100, and more preferably 690 to 1000, from the viewpoint of maintaining an appropriate distance between the particles and easiness of volatilization / decomposition of compound A itself.

A specific example of the compound A described above is a compound represented by the following formula (I) or (II).

In the formula (I), v and y are independently integers of 1 to 2, w is an integer of 0 to 10, and x is an integer of 14 to 40. Note that-(CH = CH) w- (CH ₂ ) x- has a block-like structure in which w (CH = CH) are continuously connected and then _{x (CH 2) are continuously connected.} Alternatively, it may have a random structure in which (CH = CH) and (CH _{2) are randomly arranged.} Further, w is preferably an integer of 0 to 8, and x is preferably an integer of 18 to 36.

Further, in the formula (II), R ¹ is an organic group containing a hydrogen atom, a carboxyl group, a hydroxyl group, an alkoxyl group or an alkyl group having 1 to 10 carbon atoms. p is an integer of 1 to 20, and m is an integer of 1 to 5. When m is 2 or more, a plurality of R ^1s may be the same or different from each other, and a plurality of − (CH ₂ ) _p − may be the same or different from each other.

The Hypermer KD9 (manufactured by Croda International plc) used in Examples 1 and 3 below is an example of the compound represented by the formula (II), and BYK-R606 (Big Chemie Japan) used in Example 2 below. (Manufactured by Co., Ltd.) is an example of a compound represented by the formula (I).

The content of the compound A described above in the embodiment of the bonding material of the present invention fully exerts its function, and the compound A is contained as an organic component in the metal bonding layer formed by performing the bonding. From the viewpoint of preventing the residue, it is preferably 0.02 to 0.8% by mass, more preferably 0.04 to 0.6% by mass, and further preferably 0.05 to 0.3% by mass. be.

<Solvent>
Embodiments of the bonding material of the present invention include a solvent. As the solvent, a small metal particle powder and a large metal particle powder can be dispersed, and a solvent having substantially no reactivity with the components in the bonding material can be widely used.

The content of the solvent in the bonding material is preferably 2 to 18% by mass, more preferably 2.5 to 16% by mass. A polar solvent or a non-polar solvent can be used as this solvent, but it is preferable to use a polar solvent from the viewpoint of compatibility with other components in the bonding material and an environmental load.

An example of a polar solvent is water;
Tarpineol, texanol, phenoxypropanol, 1-octanol, 1-decanol, 1-dodecanol, 1-tetradecanol, Telsolve MTPH (manufactured by Nippon Terpen Chemical Co., Ltd.), dihydroterpinyloxyethanol (manufactured by Nippon Terpen Chemical Co., Ltd.) , Telsolve TOE-100 (manufactured by Nippon Telpen Chemical Co., Ltd.), Telsolve DTO-210 (manufactured by Nippon Telpen Chemical Co., Ltd.) and other monoalcohols;
3-Methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol (octanediol), hexyldiglycol, 2-ethylhexylglycol, dibutyldiglycol, glycerin, dihydroxytriol, 3-methylbutane-1, 2,3-Triol (Isoplentriol A (IPTL-A), manufactured by Nippon Telpen Chemical Co., Ltd.), 2-Methylbutane-1,2,4-Triol (Isoplentriol B (IPTL-B), manufactured by Nippon Telpen Chemical Co., Ltd.) ) And other polyols;
Ether compounds such as butyl carbitol, diethylene glycol monobutyl ether, turpinylmethyl ether (manufactured by Nippon Terpen Chemical Co., Ltd.), dihydroterpinyl methyl ether (manufactured by Nippon Terpen Chemical Co., Ltd.);
Glycol ether acetate such as butyl carbitol acetate, diethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate;
Nitrogen-containing cyclic compounds such as 1-methylpyrrolidinone and pyridine;
γ-Butyrolactone, methoxybutyl acetate, methoxypropyl acetate, ethyl lactate, 3-hydroxy-3-methylbutyl acetate, dihydroterpinyl acetate, Telsolv IPG-2Ac (manufactured by Nippon Telpen Chemical Co., Ltd.), Telsolv THA-90 (Japan) Ester compounds such as Telpen Chemical Co., Ltd.) and Telsolve THA-70 (manufactured by Nippon Telpen Chemical Co., Ltd.);
Etc. can be used. These may be used alone or in combination of two or more.

Hereinafter, preferred examples and modified examples of the present invention will be described.

<Powder of particles in metal>
An embodiment of the bonding material of the present invention may include particle powder in a metal having a cumulative 50% particle diameter (D50) of 0.4 to 4.7 μm based on a volume measured by a laser diffraction type particle size distribution measuring device. The content thereof is preferably 40 to 85% by mass. By containing a specific amount of such a powder of a specific size, crack generation is more effectively prevented in the metal bonding layer formed from the bonding material. The present inventors speculate the mechanism as follows.

When the bonding material contains a metal powder having a large particle diameter (the large metal particle powder) as in the embodiment of the bonding material of the present invention, the coating film formed by applying the bonding material to a substrate or the like The powder functions as a spacer. Due to this function, the heat shrinkage in the thickness direction of the coating film due to firing is suppressed, while the heat shrinkage in the horizontal direction is strengthened. However, in the case of this preferred example, a considerable amount (40 to 85% by mass) of particle powder in the metal, which causes sintering but has weak sinterability, is contained in the bonding material, and the sintering structure (40 to 85% by mass) of the powder is contained. = The skeleton of the metal bonding layer) is formed. Since the medium particle powder and the large metal particle powder have weak or substantially no sinterability, their thermal shrinkage is very small. The small metal particle powder has strong heat shrinkage, but since the skeleton of the sintered structure is formed by the above-mentioned medium particle powder in metal, it is considered that the heat shrinkage at the time of formation is weak for the entire metal bonding layer. .. It is considered that the above mechanism alleviates the thermal shrinkage during the formation of the metal bonding layer and prevents the generation of cracks in the bonding layer.

From the above estimation mechanism (from the viewpoint of forming the skeleton of an appropriate sintered structure by the appropriate sinterability of the particle powder in the metal), the cumulative 50% particle diameter (D50) of the particle powder in the metal is preferably 1. .1 to 4.5 μm.

From the viewpoint that the particle powder in the metal forms the skeleton of the above-mentioned sintered structure, from the viewpoint of securing the amount of the small metal particle powder in the bonding material to form a strong metal bonding layer, and the large metal particles in the bonding material. From the viewpoint of securing the amount of the powder and sufficiently exerting its function as a spacer, the content of the particle powder in the metal is more preferably 42 to 80% by mass.

The constituent metals of the medium particle powder in the metal are the same as in the case of the large metal particle powder and the small metal particle powder, and silver, copper, gold, and aluminum are preferable from the viewpoint of heat dissipation and conductivity. Of these, alloys of two or more kinds of metals may be used. As the constituent metal, silver is particularly preferable from the viewpoint of heat dissipation, conductivity and cost. From the viewpoint of forming a metal bonding layer having the same linear expansion coefficient and excellent bonding reliability, the metal small particle powder, the metal medium particle powder, and the metal large particle powder are made of the same metal or alloy. Is preferable.

The shape of the particle powder in the metal is not particularly limited. It may have any shape such as substantially spherical (average aspect ratio of 1 to 1.5 described later), flakes, and irregular shape, but the substantially spherical particle powder in the metal has a strong sintered structure with improved particle filling property. It is preferable because it can form a skeleton.

The particle powder in the metal may be coated with an organic compound from the viewpoint of increasing the dispersibility in the bonding material and enabling dense filling. As the organic compound, a known organic compound capable of covering the particle surface of the particle powder in the metal can be used without particular limitation. Examples of the organic compound include organic compounds having 12 to 24 carbon atoms having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a thiol group and a disulfide group. The organic compound may have branches and may be saturated or unsaturated. Examples of such organic compounds include lauric acid, myristic acid, margaric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, myristoleic acid, palmitic acid and the like.

The amount of the organic compound in the particle powder in metal is 0.05 to 1.8% by mass in 100% by mass of the particle powder in metal (including the organic compound that coats the particles) from the viewpoint of dispersibility. It is preferably 0.1 to 1.2% by mass, and more preferably 0.1 to 1.2% by mass.

Further, the total content of the metal small particle powder and the metal medium particle powder in the bonding material is preferably 70% by mass or more. When the bonding material contains the metal small particle powder and the metal medium particle powder in a high content as described above, a metal bonding layer having excellent bonding reliability can be formed from the bonding material. If the total is too large, the viscosity of the bonding material (affecting printing characteristics) may increase, and the amount of large metal particle powder that functions as a spacer may not be secured. From these viewpoints, the total content of the metal small particle powder and the metal medium particle powder in the bonding material is preferably 75 to 92% by mass.

The ratio (D50 _L / D50 _M ) of the cumulative 50% particle size (D50 _L ) of the large metal particle powder to the cumulative 50% particle size (D50 _M ) of the medium particle powder is formed from the medium particle powder. From the viewpoint of reducing the gap generated between the skeleton of the sintered structure and the particles of the large metal particle powder (and filling the gap with the particles of the small metal particle powder) to more effectively reduce the occurrence of cracks, 5 It is preferably ~ 20.

Furthermore, from the viewpoint that the metal small particle powder, the metal medium particle powder and the metal large particle powder exert their respective functions well, the total content (mass ratio) of the metal small particle powder and the metal medium particle powder in the bonding material is added. , The ratio (small metal particle powder + medium particle powder: large metal particle powder) to the content (mass ratio) of the large metal particle powder in the bonding material is 1: 0.02 to 1: 0.3. It is preferably 1: 0.08 to 1: 0.2, and more preferably 1: 0.08 to 1: 0.2.

<Other ingredients (additives)>
Embodiments of the bonding material of the present invention may contain additives known as other components. Specifically, as additives, dispersants such as acid-based dispersants, sintering accelerators such as glass frit, antioxidants, viscosity regulators, pH adjusters, buffers, defoamers, leveling agents, and volatilization suppression. Agents are mentioned. The content of the additive in the bonding material is preferably 2% by mass or less (when a plurality of types of additives are contained, the total content is 2% by mass or less). When the bonding material contains an additive, the content thereof is usually 0.005% by mass or more (when a plurality of types of additives are contained, the content of each is 0.005% by mass or more).

There is a type of bonding material in which a resin is mixed to function as a binder between small metal particle powders, but a type of resin that functions as a binder between small metal particle powders is a metal formed from the bonding material. It remains in the bonding layer and may adversely affect heat dissipation and conductivity. Even in the case of conductive particles in which resin particles are coated with silver, copper, or the like, the resin portion adversely affects heat dissipation and the like. Further, since the resin has a coefficient of linear expansion significantly different from that of the metal, stress is generated due to the above difference when the metal bonding layer is subjected to a thermal cycle, which adversely affects the bonding reliability.

From the above, it is preferable that the resin (excluding the compound corresponding to the compound A in the present invention) is substantially not blended in the embodiment of the bonding material of the present invention. Specifically, the content of the resin in the bonding material is preferably 0.3% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0.05% by mass or less. preferable.

[Manufacturing method of bonding material]
An embodiment of the bonding material of the present invention comprises the above-described small metal particle powder (preferably medium particle powder in metal), large metal particle powder, compound A and solvent, and other optional components (for example, additives). It can be produced by mixing by a known method. The amount of each component used is such that the content of each component in the bonding material is calculated from the amount of each component charged and is the amount explained above (that is, for example, of a small metal particle powder). The content is preferably 7 to 55% by mass, the content of the particle powder in the metal is preferably 40 to 85% by mass, and the content of the large metal particle powder is preferably 2 to 20% by mass). ..

The mixing method is not particularly limited. For example, each component is prepared individually, and in any order, an ultrasonic disperser, a disper, a three-roll mill, a ball mill, a bead mill, a twin-screw kneader, a planetary mixer, etc. Alternatively, the bonding material can be manufactured by mixing with a revolving rotation type stirrer or the like.

[Joining method]
In the embodiment of the joining method of the present invention, two members to be joined are joined by using the joining material manufactured by the embodiment of the joining material of the present invention or the embodiment of the method of manufacturing the joining material of the present invention. How to do it. The embodiment of the bonding method of the present invention includes a coating film forming step, a mounting step, and a metal bonding layer forming step, and may also carry out a pre-drying step and the like. Hereinafter, each of these steps will be described.

<Coating film forming process>
In this step, the bonding material produced according to the embodiment of the bonding material of the present invention or the method of manufacturing the bonding material of the present invention is printed on one of the members to be bonded (for example, metal mask printing, screen printing). Apply by printing, pin transfer, dispense), etc. to form a coating film. An example of the one of the members to be joined is a substrate. As the substrate, a metal substrate such as a copper substrate, an alloy substrate of copper and some kind of metal (for example, W (tungsten) or Mo (molybdenum)), a SiN (silicon nitride) plate or an AlN (aluminum nitride) plate sandwiched between copper plates. Examples thereof include a ceramic substrate, a plastic substrate such as a PET (polyethylene terephthalate) substrate, and a PCB substrate such as FR4. Further, a laminated substrate in which these are laminated can also be used in the joining method of the present invention.

The portion to which the bonding material of one of the members to be bonded is applied may be plated with metal. The metal small particle powder having high sinterability and atomic diffusivity has a great influence on the bonding between the metal bonding layer formed from the coating film and the member to be bonded. From the viewpoint of bonding compatibility with the small metal particle powder in the coating film, it is preferable that the metal plating is a plating of the same metal as the constituent metal of the small metal particle powder.

<Placement process>
Subsequently, the other member to be joined is placed on the coating film formed on the one member to be joined. Examples of the other member to be joined include semiconductor devices such as Si elements, SiC, and GaN elements, and the same substrate as mentioned as an example of one member to be joined. Since crack generation is prevented from the coating film and therefore a metal bonding layer having excellent reliability and conductivity can be formed, the embodiment of the bonding method of the present invention is used for bonding a substrate and a semiconductor element. It is preferable to be done. That is, a semiconductor element is preferable as the other member to be joined.

The portion (bottom surface) of the other member to be joined that comes into contact with the coating film may be plated with metal. From the viewpoint of bonding compatibility with the small metal particle powder in the coating film, it is preferable that the metal plating of the other member to be bonded is the same metal plating as the constituent metal of the small metal particle powder. Further, when the other member to be joined is placed on the coating film, a pressure in the direction of compressing the coating film may or may not be applied between the two members to be joined.

<Preliminary drying process>
The coating film on which the other member to be bonded is placed is heated to form a small metal particle powder (preferably the powder and the particle powder in the metal. Hereinafter, the coating film formed from the bonding material) is the particle powder in the metal. Before or after mounting the other member to be bonded on the coating film (before or after the mounting step), a pre-drying step of pre-drying the coating film is performed. It may be carried out. The pre-drying is intended to remove the solvent from the coating film, and is dried under conditions such that the solvent volatilizes and the small metal particle powder and the medium particle powder do not substantially cause sintering. The condition that compound A is not substantially lost during this drying is adopted. Specifically, the pre-drying is preferably carried out by heating the coating film at 60 to 150 ° C. Drying by this heating may be performed under atmospheric pressure, or may be performed under reduced pressure or vacuum. Further, in the metal bonding layer forming step described below, if the rate of temperature rise to the firing temperature is about 7 ° C./min or less, the preliminary drying step can be carried out by raising the temperature to the firing temperature.

<Metal bonding layer forming process>
After carrying out the mounting step and, if necessary, the pre-drying step, the coating film sandwiched between the two members to be joined is calcined at 160 to 350 ° C. to obtain the metal small particle powder and the metal medium particle powder. By sintering, a metal bonding layer is formed and the two members to be bonded are bonded. By this step, the skeleton of the sintered structure formed from the metal medium particle powder and the metal large particle powder were connected by the sintered metal small particle powder (although the shape of the particles does not usually remain) and were continuous. A dense metal bonding layer is formed.

In the metal bonding layer forming step, the temperature is raised to the firing temperature of 160 to 350 ° C., and the temperature is maintained at the firing temperature for, for example, 1 minute to 2 hours to form the metal bonding layer from the coating film of the bonding material. The rate of temperature rise is not particularly limited, but can be, for example, 1.5 ° C./min to 10 ° C./min, preferably 2 ° C./min to 6 ° C./min.

The firing temperature is preferably 175 to 280 ° C. from the viewpoint of the bonding strength and cost of the formed metal bonding layer.

The time for holding at the firing temperature is preferably 10 to 90 minutes from the viewpoint of the bonding strength and cost of the formed metal bonding layer. If the firing temperature is higher than the firing temperature range shown above, such as 280 ° C. or higher, a metal bonding layer may be formed before the temperature rises to the firing temperature. In such a case, the holding time at the firing temperature may be 0 minutes.

Further, in this metal bonding layer forming step, it is not necessary to apply a pressure (in the direction of compressing the coating film) between the members to be bonded, but a pressure of 5 MPa or less (usually 15 Pa or more) may be applied. When the metal bonding layer is formed by pressure firing to apply pressure as described above, the sandwich structure of the member to be bonded-coating film-member to be bonded is pressure-fired one by one to perform bonding. If so, productivity is very low. In order to increase productivity, it is conceivable to pressurize and bake many sandwich structures at the same time, but it is not easy to apply the same pressurization to the sandwich structures in the same direction at the same time, and at the same time. When pressure firing is performed, there is a concern about the uniformity of the quality of the obtained product. From the above, in the present invention, it is preferable to carry out the metal bonding layer forming step without pressurizing (that is, under atmospheric pressure or reduced pressure) to form the metal bonding layer.

Further, the metal bonding layer forming step may be carried out in an atmospheric atmosphere or in an inert atmosphere such as a nitrogen atmosphere.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

<Preparation of small silver particle powder 1>
A small silver particle powder 1 coated with caproic acid having an average primary particle diameter of 20 nm was prepared as follows.

3400 g of water is put into a 5 L reaction vessel, nitrogen is flowed into the water in the reaction vessel for 600 seconds at a flow rate of 3000 mL / min from a nozzle provided at the bottom of the reaction vessel to remove dissolved oxygen, and then from the upper part of the reaction vessel. Nitrogen is supplied into the reaction vessel at a flow rate of 3000 mL / min to create a nitrogen atmosphere in the reaction vessel, and the temperature of the water in the reaction vessel is 60 while stirring with a stirring rod equipped with a stirring blade provided in the reaction vessel. Adjusted to ℃. After adding 7 g of ammonia water having a concentration of 28% by mass to the water in the reaction vessel, the mixture was stirred for 1 minute to obtain a uniform solution. After adding 45.5 g (molar ratio to silver is 1.98) of a saturated fatty acid, hexanoic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as an organic compound to the solution in this reaction vessel and stirring for 4 minutes to dissolve the solution. , 23.9 g (4.82 equivalent with respect to silver) of hydrazine hydrate (manufactured by Otsuka Chemical Co., Ltd.) in an amount of 50% by mass was added as a reducing agent to prepare a reducing agent solution.

In addition, a silver nitrate aqueous solution prepared by dissolving 33.8 g of silver nitrate crystals (manufactured by Wako Pure Chemical Industries, Ltd.) in 180 g of water was prepared as a silver salt aqueous solution, and the temperature of this silver salt aqueous solution was adjusted to 60 ° C. 0.00008 g (1 ppm in terms of copper with respect to silver) of copper nitrate trihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the silver salt aqueous solution. The addition of copper nitrate trihydrate was carried out by adding an aqueous solution obtained by diluting an aqueous solution of copper nitrate trihydrate having a high concentration to some extent so as to add the target amount of copper.

Next, the above-mentioned silver salt aqueous solution was added to the above-mentioned reducing agent solution all at once, mixed, and the reduction reaction was started while stirring. About 10 seconds after the start of this reduction reaction, the color change of the slurry as the reaction solution was completed, and after aging for 10 minutes while stirring, the stirring was finished and solid-liquid separation by suction filtration was performed to obtain the obtained product. The solid was washed with pure water and vacuum dried at 40 ° C. for 12 hours to obtain a dry powder of substantially spherical small silver particle powder 1 (coated with hexaxic acid).

The ratio of silver in the small silver particle powder 1 is 97% by mass from the weight after raising the temperature from room temperature to 700 ° C. in a muffle furnace and holding at 700 ° C. for 10 minutes to remove the hexane acid. It was calculated that there was (thus, the amount of hexanoic acid in the small silver particle powder 1 is 3% by weight). Further, when the average primary particle diameter of the small silver particle powder 1 was determined by a transmission electron microscope (TEM), it was 20 nm.

<Preparation of small silver particle powder 2>
An aqueous silver nitrate solution was prepared as a raw material solution by putting 180.0 g of pure water in a 300 mL beaker and adding 33.6 g of silver nitrate (manufactured by Toyo Kagaku Co., Ltd.) to dissolve it.

Further, 3322.0 g of pure water was placed in a 5 L beaker, and nitrogen was aerated in the pure water for 30 minutes to remove dissolved oxygen, and the temperature was raised to 40 ° C. After adding 44.8 g of sorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as an organic compound (for coating silver fine particle powder) to this pure water, ammonia water (Wako Pure Chemical Industries, Ltd.) having a concentration of 28% by mass as a stabilizer is added. (Manufactured by Kogyo Co., Ltd.) 7.1 g was added.

While stirring the aqueous solution after adding the ammonia water, 14.91 g of water-containing hydrazine (manufactured by Otsuka Chemical Co., Ltd.) having a purity of 80% was added as a reducing agent 5 minutes after the addition of the ammonia water (at the start of the reaction). The mixture was added to prepare a reducing agent-containing aqueous solution as a reducing solution. After 9 minutes have passed from the start of the reaction, the raw material solution (silver nitrate aqueous solution) whose temperature was adjusted to 40 ° C. was added to the reducing solution (reducing agent-containing aqueous solution) at once to react, and the mixture was further stirred for 80 minutes, and then ascended. The liquid temperature was raised from 40 ° C. to 60 ° C. at a temperature rate of 1 ° C./min, and stirring was completed.

After forming aggregates of silver fine particles coated with sorbic acid in this way, a liquid containing the aggregates of silver fine particles was designated as No. It was filtered with a filter paper of 5C, and the recovered product by this filtration was washed with pure water to obtain an aggregate of silver fine particles. The aggregates of silver fine particles were dried at 80 ° C. for 12 hours in a vacuum dryer to obtain a dry powder of the aggregates of silver fine particles. The dry powder thus obtained was crushed to adjust the size of the secondary aggregate to obtain a substantially spherical small silver particle powder 2.

The average primary particle diameter of the small silver particle powder 2 was determined by a scanning electron microscope (SEM) and found to be 80 nm.

<Preparation of silver medium particle powders 1 and 2>
AG2-1C (manufactured by DOWA Hightech Co., Ltd.) is used as a substantially spherical silver medium particle powder 1 having a cumulative 50% particle diameter (D50) of 0.87 μm on a volume basis measured by a laser diffraction type particle size distribution measuring device. I prepared it. The D50 uses a laser diffraction type particle size distribution measuring device (SIMPATEC's Heros particle size distribution measuring device (HELOS & RODOS (air flow type dispersion module))), a dispersion pressure of 5 bar, and a lens having a focal length of 20 mm. Then, the particle size distribution on a volume basis was obtained.
AG-3-60 (DOWA) as a substantially spherical silver medium particle powder 2 having a cumulative 50% particle diameter (D50) of 1.4 μm on a volume basis measured by a laser diffraction type particle size distribution measuring device under the same conditions as described above. High Tech Co., Ltd.) was prepared.

<Preparation of large silver particle powder>
As a large silver particle powder, the volume-based cumulative 50% particle diameter (D50) measured by a laser diffraction type particle size distribution measuring device is 19.06 μm, and the volume-based cumulative 90% particle diameter (D90) is 26.04 μm. R & D AgPowerer 27019-NM-1 R08517-00 manufactured by AMES GOLDSMITH, which is substantially spherical and has an average aspect ratio of about 1.0, was prepared. The D50 and D90 are lenses having a dispersion pressure of 5 bar and a focal length of 200 mm using a laser diffraction type particle size distribution measuring device (Hellos particle size distribution measuring device (HELOS & RODOS (air flow type dispersion module)) manufactured by SYMPATEC). It was obtained by obtaining the particle size distribution on a volume basis using. The proportion of silver in this large silver particle powder was calculated to be 99.2% by mass from the weight after removing the organic matter by heating in the same manner as in the case of the small silver particle powder 1 (hence, silver). The amount of the organic compound that coats the particles in the large particle powder is 0.8% by mass).

[Comparative Example 1]
Silver small particle powder 1 is 14.66% by mass, silver small particle powder 2 is 27.08% by mass, and silver medium particle powder is 51.3% by mass. Ethyl-1,3-hexanediol (isomer mixture) (having two hydroxyl groups and having a molecular weight of 146) 1.50% by mass, 1-dodecanol (having one hydroxyl group and having a molecular weight of 120) 1. 45% by mass and Telsolv IPTL-B (manufactured by Nippon Telpen Chemical Co., Ltd., having 3 hydroxyl groups and having a molecular weight of 120) 3.50% by mass, and BEA (butoxyethoxyacetic acid: one carboxyl group) as a dispersant. The molecular weight was 176) (manufactured by Tokyo Kasei Kogyo Co., Ltd.) and 0.50% by mass was kneaded to prepare a silver paste.

To 90 parts by mass of the silver paste, 10 parts by mass of silver large particle powder was added and kneaded to obtain a bonding material of Comparative Example 1.

This bonding material includes 13.20% by mass of small silver particle powder 1, 24.38% by mass of small silver particle powder 2, 46.17% by mass of medium particle powder in silver, and 2-ethyl-1,3-hexanediol. 1.35% by mass, dodecanol 1.30% by mass, Telsolve IPTL-B 3.15% by mass, BEA 0.45% by mass, and silver large particle powder 10.00% by mass.

In addition, Comparative Example 1 and other comparative examples described later are examples for comparison with Examples 1 to 3 described below, and are not conventional examples.

[Example 1]
The amount of each component used was changed, and when the silver paste was prepared, the compound A was Hypermer® KD9 (manufactured by Croda International plc. Hereinafter, the same applies to Hypermer) (a polycarboxylic acid having a plurality of carboxyl groups. The bonding material of Example 1 was prepared in the same manner as in Comparative Example 1 except that the weight average molecular weight Mw (measured by the GPC method) was 760) and the amount of the silver medium particle powder 1 used was slightly reduced. did.

[Examples 2 and 3 and Comparative Examples 2 to 7]
The bonding materials of Example 2 and Comparative Examples 2 to 7 were prepared in the same manner as in Example 1 except that a compound different from Hypermer KD9, which is the compound A used in Example 1, was used (Comparative Example 2). In ~ 7, a compound that does not correspond to compound A was used). In Example 3, while using Hypermer KD9, silver medium particle powder 2 having a relatively large D50 was used, and the amount of the component used was slightly changed.

The characteristics and molecular weight of the functional groups of each reagent used in each example are as follows.

(solvent)
2-Ethyl-1,3-hexanediol: 2 hydroxyl groups, molecular weight 146
1-Dodecanol: 1 hydroxyl group, molecular weight 186
-Telsolv IPTL-B: 3 hydroxyl groups, molecular weight 120

(Dispersant)
-(2-Butyloxyethoxy) acetic acid: one carboxyl group, molecular weight 176

(Compound)
Examples 1 and 3: Hypermer KD9: polycarboxylic acid, molecular weight (Mw) is 760.
Example 2: BYK-R606 (manufactured by Big Chemie Japan Co., Ltd.): 2 to 4 hydroxyl groups, molecular weight 815-830 (mixture of compounds having different molecular weights)
Comparative Example 2: Hypermer KD16: dicarboxylic acid, molecular weight is 490.
Comparative Example 3: Hypermer KD57: Dicarboxylic acid, molecular weight is 470.
-Comparative Example 4: BYK-P105 (manufactured by Big Chemie Japan Co., Ltd.): Polycarboxylic acid, molecular weight (Mw) is several thousand (2000 or more)
Comparative Example 5: Malonic acid: dicarboxylic acid, molecular weight is 104
Comparative Example 6: BTA (benzotriazole): one amino group, molecular weight 119
Comparative Example 7: Curesol 2PZ (2-phenylimidazole): One amino group, molecular weight 144

The compositions of the bonding materials of Examples 1 to 3 and Comparative Examples 1 to 7 obtained as described above are shown in Table 1 below.

[evaluation]
The following evaluations were made for each of the bonding materials manufactured in each of the above Examples and Comparative Examples.

<Joining test>
A copper substrate with a size of 10 mm x 10 mm x 1 mm degreased with ethanol and an Au-plated joint, and a semiconductor device with a size of 1.2 mm x 1.2 mm x 0.13 mm with the joint surface Au-plated. (EV-B45A, manufactured by Asahi Akira Koden (Crotch) Co., Ltd. Semi LEDs) was prepared.

Next, the bonding materials of the above Comparative Examples and Examples were applied on the copper substrate (the gold-plated portion of the pin) by pin transfer (the inner diameter of the pin was 393 μm) to form a coating film. A manual bonder (7200CR, manufactured by Westbond) is placed on this coating film so that the Au-plated portion (joint surface) of the above-mentioned semiconductor element is in contact with the coating film, and the element is coated by pressing the upper surface of the semiconductor element. After being pushed into the membrane, the temperature rises from 25 ° C to 210 ° C in an air atmosphere with an infrared lamp heating device (MILA-5000-PN, manufactured by ULVAC ULVAC-RIKO, Inc.) at a heating rate of 6 ° C / min. The baking was carried out by warming and holding at 210 ° C. for 60 minutes. As a result, a silver bonding layer was formed, and the semiconductor element was bonded to the copper substrate by this silver bonding layer. Although the bonding material of each Example and Comparative Example contains silver large particle powder, a silver bonding layer having approximately the same size (thickness) as that of D90 was formed.

(Results of imaging of the joint)
A microfocus X-ray fluoroscope (SMX-160LT, Taken at Shimadzu Corporation).

FIGS. 1 to 3 show the joint portion of the semiconductor element-silver joint layer-copper substrate of the joint obtained in the joint test using the joint materials of Examples 1 to 3 taken with a microfocus X-ray fluoroscope. It is a figure which shows the result of this.

FIGS. 4 to 10 show the joint portion of the semiconductor element-silver bonding layer-copper substrate of the bonded body obtained in the bonding test using the bonding materials of Comparative Examples 1 to 7, respectively, photographed by a microfocus X-ray fluoroscope. It is a figure which shows the result of this.

Looking at each figure related to each comparative example, it can be seen that cracks represented by white were generated in the silver bonding layer. On the other hand, looking at each figure according to each example, it can be seen that the generation of cracks in the silver bonding layer was remarkably suppressed (compared to the comparative example).

(Evaluation of joint strength)
The bonding strength of each bonded body obtained in the above bonding test was confirmed. The object to be joined (semiconductor element) joined on the copper substrate was pushed in the horizontal direction, and the force when the joined surface was broken because it could not withstand the pushing force was measured. The evaluation was performed using a bond tester (series 4000) manufactured by Nordson Dage. The shear height was 25 μm with respect to the substrate surface, the test speed was 5 mm / min, and the measurement was performed at room temperature. In the test, the force (N) at which the joint surface breaks is directly measured, and is a value that depends on the joint area. Therefore, in order to obtain the standard value, the value (MPa) obtained by dividing the measured breaking force by the joint area (1.2 (mm) x 1.2 (mm) = 1.44 mm ^{2 in this case).} Was defined as shear strength. The intensity was measured with n = 2, and the average value was obtained. The results are shown in Table 2.

As shown in Table 2, when BYK-R606 (a specific example of the above formula (I)) was used as compound A as in Example 2, relatively high bonding strength was obtained even in each example. .. Further, when a powder having a relatively high D50 value was used as the particle powder in the metal as in Example 3, high bonding strength was obtained.

Claims (19)

Small metal particle powder with an average primary particle size of 150 nm or less, large metal particle powder with a cumulative 90% particle size (D90) of 7 to 40 μm on a volume basis measured by a laser diffraction type particle size distribution measuring device, and multiple functional groups. A bonding material containing compound A having a molecular weight of 600 to 1500 and a solvent. The small metal particle powder is composed of silver, copper, gold, aluminum or an alloy of two or more of these.
The bonding material according to claim 1, wherein the large metal particle powder is composed of silver, copper, gold, aluminum, or an alloy of two or more of these. The bonding material according to claim 1 or 2, wherein the cumulative 90% particle diameter (D90) of the large metal particle powder is 18 to 35 μm. The bonding material according to any one of claims 1 to 3, wherein the functional group is a hydroxyl group, an amino group, a thiol group or a carboxyl group. The bonding material according to any one of claims 1 to 4, wherein the compound A is a compound represented by the following formula (I) or (II).

(In the formula (I), v and y are independently integers of 1 to 2, w is an integer of 0 to 10, and x is an integer of 14 to 40.
In formula (II), R ¹ is an organic group containing a hydrogen atom, a carboxyl group, a hydroxyl group, an alkoxyl group or an alkyl group having 1 to 10 carbon atoms. p is an integer of 1 to 20, and m is an integer of 1 to 5. When m is 2 or more, a plurality of R ^1s may be the same or different from each other, and a plurality of − (CH ₂ ) _p − may be the same or different from each other. ) The bonding material according to any one of claims 1 to 5, wherein the content of the small metal particle powder in the bonding material is 7 to 55% by mass. 13. Joining material. The bonding material according to claim 7, wherein the content of the particle powder in the metal in the bonding material is 40 to 85% by mass. The bonding material according to any one of claims 1 to 8, wherein the content of the large metal particle powder in the bonding material is 2 to 20% by mass. The bonding material according to any one of claims 1 to 9, wherein the small metal particle powder is composed of silver and the large metal particle powder is composed of silver. The bonding material according to any one of claims 1 to 10, wherein the metal large particle powder has an average aspect ratio of 3 or less. Small metal particle powder with an average primary particle size of 150 nm or less, large metal particle powder with a cumulative 90% particle size (D90) of 7 to 40 μm on a volume basis measured by a laser diffraction type particle size distribution measuring device, and multiple functional groups. A method for producing a bonding material, which comprises mixing compound A having a molecular weight of 600 to 1500 and a solvent. The small metal particle powder is composed of silver, copper, gold, aluminum or an alloy of two or more of these.
The method for producing a bonding material according to claim 12, wherein the large metal particle powder is composed of silver, copper, gold, aluminum, or an alloy thereof. The amount of the metal small particle powder and the metal large particle powder used is 7 to 55% by mass and the content of the metal small particle powder and the metal large particle powder in the bonding material are 7 to 55% by mass and 2 to 20% by mass, respectively. The method for producing a bonding material according to claim 12 or 13, which is an amount thereof. The method for producing a bonding material according to any one of claims 12 to 14, wherein the compound A is a compound represented by the following formula (I) or (II).

(In the formula (I), v and y are independently integers of 1 to 2, w is an integer of 0 to 10, and x is an integer of 14 to 40.
In formula (II), R ¹ is an organic group containing a hydrogen atom, a carboxyl group, a hydroxyl group, an alkoxyl group or an alkyl group having 1 to 10 carbon atoms. p is an integer of 1 to 20, and m is an integer of 1 to 5. When m is 2 or more, a plurality of R ^1s may be the same or different from each other, and a plurality of − (CH ₂ ) _p − may be the same or different from each other. ) In addition to the small metal particle powder, large metal particle powder, compound A and a solvent, the cumulative 50% particle diameter (D50) on a volume basis measured by a laser diffraction type particle size distribution measuring device is 1.1 to 4.5 μm. The method for producing a bonding material according to any one of claims 12 to 15, wherein the particle powder in the metal is mixed. The method for producing a bonding material according to claim 16, wherein the amount of the particle powder in the metal used is such that the content of the particle powder in the metal in the bonding material is 40 to 85% by mass. It is a joining method that joins two members to be joined.
A coating film is coated on one of the members to be joined by applying the bonding material according to any one of claims 1 to 11 or the bonding material manufactured by the method for producing a bonding material according to any one of claims 12 to 17. And the process of forming
The step of placing the other member to be joined on the coating film, and
A bonding method comprising a step of firing a coating film on which the other member to be bonded is placed at 160 to 350 ° C. to form a metal bonding layer from the coating film. The joining method according to claim 18, wherein one of the members to be joined is a substrate and the other member to be joined is a semiconductor element.

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