JP7200527B2 - METAL PASTE FOR JOINING AND METHOD FOR MANUFACTURING JOINT - Google Patents

Description

TECHNICAL FIELD The present invention relates to a joining metal paste, a joined body, and a method for producing the joined body.

2. Description of the Related Art When manufacturing a semiconductor device, various bonding materials are used to bond a semiconductor element and a lead frame or the like (supporting member). Among semiconductor devices, high-melting-point lead solder has been used as a bonding material for bonding power semiconductors, LSIs, and the like that operate at high temperatures of 150° C. or higher. In recent years, the operating temperature has risen to near the melting point of high-melting-point lead solder due to the increase in capacity and space saving of semiconductor devices, making it difficult to ensure connection reliability. On the other hand, with the tightening of RoHS regulations, there is a demand for jointing materials that do not contain lead.

So far, studies have been made on bonding semiconductor elements using materials other than lead solder. For example, Patent Document 1 below proposes a technique for forming a sintered silver layer by sintering silver nanoparticles at a low temperature.

As yet another material, a technique of sintering copper particles to form a sintered body (sintered copper layer) has been proposed. For example, Patent Document 2 below discloses a bonding paste containing cupric oxide particles and a reducing agent as a bonding material for bonding a semiconductor element and an electrode. Further, Patent Document 3 below discloses a bonding material containing copper nanoparticles, copper microparticles or copper submicroparticles, or both. A die-bonding material that uses sintering of copper particles has excellent thermal conductivity and cycle fatigue resistance, and is inexpensive, so it is attracting attention as a material that can replace lead solder.

Patent No. 4928639 Patent No. 5006081 JP 2014-167145 A

The method described in Patent Literature 1 requires a thermocompression bonding process accompanied by pressurization because the sintered silver layer must be densified in order to obtain high connection reliability. When performing a thermocompression bonding process involving pressurization, there are problems such as a decrease in production efficiency and a decrease in yield. Furthermore, when silver nanoparticles are used, a significant increase in material cost due to silver poses a problem.

The method described in Patent Document 2 avoids volumetric shrinkage during reduction of copper oxide to copper by a thermocompression bonding process. However, the thermocompression bonding process has the problems described above.

The method described in Patent Document 3 performs sintering without pressure, but is still insufficient for practical use in the following respects. In other words, it is necessary to modify the surface of copper nanoparticles with a protective agent to suppress oxidation and improve dispersibility. There is a tendency for the compounding amount of the surface protective agent to increase. In addition, there is a tendency to increase the blending amount of the dispersion medium in order to ensure dispersibility. Therefore, the bonding material described in Patent Document 3 has a large proportion of a surface protective agent or a dispersion medium for supply stability during storage, coating, etc., and volume shrinkage during sintering tends to increase, In addition, it is difficult to ensure the strength of the sintered body because the denseness tends to decrease after sintering.

The present invention provides a bonding metal paste capable of obtaining sufficient bonding strength even when bonding is performed without pressure, a bonded body using the bonding metal paste, and a method for manufacturing the same. for the purpose.

The present inventors used a combination of flaky copper particles with a large particle size and copper particles with a small particle size as the metal particles in the metal paste, and when the metal paste was applied or printed, By forming a structure consisting of flake-shaped copper particles oriented approximately parallel to each other and copper particles dispersed between the flake-shaped copper particles, the bonding strength at the time of bonding without pressure (non-pressure bonding) was found to be able to improve Further, it was found that the bonding strength during non-pressure bonding can be further improved by using a specific polyethylene glycol in addition to a specific dispersion medium suitable for forming the above structure, thus completing the present invention. let me

One aspect of the present invention relates to a bonding metal paste containing metal particles and a dispersion medium for dispersing the metal particles. In this metal paste, the metal particles include first flaky copper particles having a particle size of 2 μm or more and second copper particles having a particle size of 0.8 μm or less, and the dispersion medium is Dispersion medium 1 contains an organic compound having a boiling point of 235° C. or less and a weight average molecular weight of 130 to 170, and polyethylene glycol having a weight average molecular weight of 200 to 600.

According to the metal paste, sufficient bonding strength can be obtained even when bonding is performed without pressure. Although the reason why such an effect is obtained is not clear, the present inventors speculate as follows.

That is, since the metal paste contains the first dispersion medium having a weight average molecular weight of 130 to 170 as a dispersion medium, the metal particles can be well dispersed, and the first dispersion medium can be dispersed during application or printing of the metal paste. The second copper particles can be dispersed among the first copper particles while the copper particles are oriented substantially parallel to the bonding interface. That is, according to the metal paste, the structure is composed of the first flaky copper particles oriented substantially parallel to the bonding interface and the second copper particles dispersed between the first flaky copper particles. can be formed. Such a structure improves the bonding strength at the time of bonding without pressure (non-pressure bonding). Furthermore, when the metal paste does not contain the second dispersion medium, the dispersion medium evaporates during sintering of the copper particles or during drying before sintering, resulting in the collapse of the above structure and a reduction in the effect of improving the bonding strength. However, in the metal paste, since the structure is maintained by the second dispersion medium, a high bonding strength improvement effect can be obtained. The inventors presume that the above effects are obtained for the reasons described above. The reason why the bonding strength is improved by the above structure is not clear, but the volume shrinkage during sintering is suppressed, the overlapping area of the flake-shaped first copper particles increases, and the flake-shaped It is believed that the first copper particles align the second copper particles to provide a reinforcing effect.

In addition, when the metal paste does not contain the second dispersion medium, the bonding strength may vary depending on the time from application of the metal paste to the sintering of the copper particles, and the difference in conditions such as the surrounding environment such as temperature. However, according to the metal paste, it is possible to suppress the occurrence of such variations in bonding strength. That is, according to the metal paste, the influence of the environment during manufacturing of the bonded body is less likely to occur, and the production stability of the bonded body such as a semiconductor device can be further improved. The reason why such an effect is obtained is that when the metal paste does not contain the second dispersion medium, volatilization of the first dispersion medium progresses and the bonding strength decreases, whereas in the above metal paste, It is conceivable that the structure formed by the first copper particles and the second copper particles is maintained by the second dispersion medium.

The dispersion medium preferably contains polyethylene glycol having a weight average molecular weight of 350 to 450 as the second dispersion medium.

The content of the second dispersion medium is preferably 4 to 14 parts by mass with respect to 100 parts by mass of the metal particles.

The content of the first dispersion medium is preferably 2 to 15 parts by mass with respect to 100 parts by mass of the metal particles.

The mass ratio of the content of the second dispersion medium to the content of the first dispersion medium is preferably 0.3 to 3.0.

The aspect ratio of the first copper particles is preferably 3.0 or more.

The first copper particles preferably contain 50% by mass or more of copper particles having a particle size of 2 to 50 μm, and the second copper particles include copper particles having a particle size of 0.12 to 0.8 μm. It is preferable to contain 20% by mass or more.

The content of the first copper particles is preferably 10 to 70% by mass based on the total mass of the metal particles, and the content of the second copper particles is based on the total mass of the metal particles. , preferably 30 to 90% by mass.

The metal particles preferably further contain at least one metal particle selected from the group consisting of zinc particles and silver particles in an amount of 0.01 to 10% by mass based on the total mass of the metal particles.

Another aspect of the present invention is to prepare a laminate in which a first member, the above-described metal paste, and a second member are laminated in this order, and apply the metal paste to receive the weight of the first member. The present invention relates to a method for manufacturing a bonded body, comprising a step of sintering at 300° C. or less in a state where the first member is pressed or subjected to the weight of the first member and a pressure of 0.01 MPa or less.

At least one of the first member and the second member may be a semiconductor device. That is, the method for manufacturing a bonded body may be a method for manufacturing a semiconductor device.

Another aspect of the present invention relates to a joined body comprising a first member, a second member, and the sintered body of the metal paste described above that joins the first member and the second member. .

At least one of the first member and the second member may contain at least one metal selected from the group consisting of copper, nickel, silver, gold and palladium on the surface in contact with the sintered body.

At least one of the first member and the second member may be a semiconductor device. That is, the junction may be a semiconductor device.

According to the present invention, there is provided a bonding metal paste capable of obtaining sufficient bonding strength even when bonding is performed without pressure, a bonded body using the bonding metal paste, and a manufacturing method thereof. can provide.

FIG. 2 is a schematic cross-sectional view showing an example of a joined body manufactured using the joining metal paste of the present embodiment; 1 is a schematic cross-sectional view showing an example of a bonded body (semiconductor device) manufactured using the bonding metal paste of the present embodiment; FIG. FIG. 2 is a schematic cross-sectional view showing an example of a joined body manufactured using the joining metal paste of the present embodiment; FIG. 2 is a schematic cross-sectional view showing an example of a joined body manufactured using the joining metal paste of the present embodiment;

In this specification, unless otherwise specified, the exemplified materials can be used singly or in combination of two or more. The content of each component in the metal paste means the total amount of the plurality of substances present in the metal paste unless otherwise specified when there are multiple substances corresponding to each component in the metal paste. A numerical range indicated using "-" indicates a range including the numerical values before and after "-" as the minimum and maximum values, respectively. In the numerical ranges described stepwise in this specification, the upper limit value or lower limit value of the numerical range at one step may be replaced with the upper limit value or lower limit value of the numerical range at another step. Moreover, in the numerical ranges described in this specification, the upper and lower limits of the numerical ranges may be replaced with the values shown in the examples. Moreover, the upper limit value and lower limit value described herein can be arbitrarily combined. The term "layer" includes not only a shape structure formed over the entire surface but also a shape structure formed partially when observed as a plan view. Moreover, in this specification, the boiling point is the boiling point at 1 atmosphere, and the viscosity is the viscosity at room temperature (25°C).

Preferred embodiments of the present invention are described below. However, the present invention is by no means limited to the following embodiments.

<Metal paste>
The metal paste of the present embodiment is, for example, a bonding material (bonding metal paste) used for bonding a plurality of members. This metal paste contains metal particles and a dispersion medium for dispersing the metal particles. and a second copper particle having a boiling point of 235 ° C. or less and a weight average molecular weight of 130 to 170 (first dispersion medium) as a dispersion medium, and a weight average molecular weight of 200 ∼600 polyethylene glycol (second dispersion medium).

According to the metal paste of the present embodiment, sufficient bonding strength can be obtained even when bonding is performed without pressure. Therefore, according to the metal paste of the present embodiment, a thermocompression bonding process involving pressurization becomes unnecessary, and production efficiency and yield can be improved. Moreover, according to the metal paste of the present embodiment, it is possible to suppress the occurrence of variations in bonding strength due to the environment during manufacturing of the bonded body. That is, according to the metal paste of the present embodiment, performance such as bonding strength of the bonded body is less likely to be affected by the environment during manufacturing, and production stability of bonded bodies such as semiconductor devices can be further improved. Moreover, since the metal particles are dispersed in the first dispersion medium, the metal paste of the present embodiment does not have an excessively high viscosity, and therefore tends to be excellent in coatability.

(metal particles)
In the present embodiment, since the metal paste contains both the first copper particles and the second copper particles and contains the first dispersion medium, volume shrinkage and sintering shrinkage due to drying are unlikely to increase. When the metal paste is sintered, it becomes difficult to separate from the adherend surface. That is, by using the first copper particles, the second copper particles, and the first dispersion medium together, the volume shrinkage when the metal paste is sintered is suppressed, and even in pressureless bonding, The bonded body can have more sufficient bonding strength. When the metal paste of the present embodiment is used for joining semiconductor elements, an effect is obtained that the semiconductor device exhibits better die shear strength and connection reliability.

The metal particles may contain copper particles other than the first copper particles and the second copper particles, and may contain metal particles other than the copper particles. The copper particles may contain metals other than copper that are inevitably contained, but are particles that consist essentially of copper. In this specification, for convenience, an aggregate of a plurality of metal particles may be referred to as "metal particles". The same applies to copper particles.

[First copper particles]
The first copper particles preferably contain copper particles having a particle size of 2 to 50 μm. The first copper particles can contain, for example, 50% by mass or more of copper particles having a particle size of 2 to 50 μm. From the viewpoint of orientation in the bonded body, reinforcing effect, and filling properties of the bonding paste, the content of the copper particles having a particle size of 2 to 50 μm in the first copper particles is 70% by mass or more, 80% by mass or more, or 90% by mass. % or more, or 100% by mass. That is, the first copper particles may be copper particles having a particle size of 2 to 50 μm.

The particle size of the copper particles can be calculated, for example, from an SEM image. Specifically, first, a powder of copper particles is placed on a carbon tape for SEM with a spatula to obtain a sample for SEM. This sample for SEM is observed at 5000 times with an SEM apparatus. A rectangle circumscribing the copper particles in the SEM image is drawn using image processing software, and one side of the rectangle is defined as the grain size of the particle. When the circumscribing quadrilateral is a rectangle, the long side is taken as the grain size (maximum diameter) of the grain.

The volume average particle size of the first copper particles may be 2-50 μm. If the volume average particle diameter of the first copper particles is within the above range, the volume shrinkage when the metal paste is sintered can be sufficiently reduced, and the bonding strength of the joined body produced by sintering the metal paste can be increased. When the metal paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit better die shear strength and connection reliability. From the viewpoint of achieving the above effect, the volume average particle diameter of the first copper particles may be 3 to 50 μm, or may be 3 to 20 μm.

As used herein, the volume average particle size means a 50% volume average particle size. When determining the volume average particle size of copper particles, the raw material copper particles or the dry copper particles obtained by removing volatile components from the metal paste are dispersed in a dispersion medium using a dispersant, and the particle size distribution is measured by the light scattering method. Apparatus (for example, Shimadzu nanoparticle size distribution measuring apparatus (SALD-7500nano, manufactured by Shimadzu Corporation) can be determined by a method of measurement, etc. As the dispersion medium, the dispersion medium described later (first dispersion medium and second 2 dispersion medium) is used.

The shape of the first copper particles is flaky. By using flaky copper particles as the first copper particles, the first copper particles in the metal paste are oriented substantially parallel to the bonding surface, so that the volume when the metal paste is sintered Shrinkage can be suppressed, and it becomes easy to ensure the bonding strength of the bonded body manufactured by sintering the metal paste. When a metal paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of easily obtaining such effects, the aspect ratio of the flaky copper particles is preferably 3.0 or more, more preferably 4.0 or more, and still more preferably 6.0 or more. In addition, in this specification, "flake-like" includes plate-like shapes such as a plate-like shape and a scale-like shape. Also, as used herein, the term "aspect ratio" indicates the long side/thickness of a particle. Particle long sides and thickness measurements can be obtained, for example, from SEM images of the particles.

The maximum diameter and average maximum diameter of the first copper particles may be 2 to 50 μm, 3 to 50 μm, or 3 to 20 μm. The maximum diameter and average maximum diameter of the flaky copper particles can be obtained, for example, from an SEM image of the particles, and obtained as the long diameter X and the average long diameter Xav of the flaky copper particles. The major axis X is the distance of two parallel planes selected so that the distance between these two parallel planes is the maximum among the two parallel planes circumscribing the flaky copper particles in the three-dimensional shape of the flaky copper particles. be.

The first copper particles may be treated with a specific surface treatment agent. Specific surface treatment agents include, for example, organic acids having 8 to 16 carbon atoms. Examples of organic acids having 8 to 16 carbon atoms include caprylic acid, methylheptanoic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid, methyloctanoic acid, ethylheptanoic acid, propylhexanoic acid, capric acid, methylnonanoic acid, ethyl octanoic acid, propylheptanoic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanoic acid, lauric acid, methylundecanoic acid, ethyldecanoic acid, propylnonanoic acid, butyloctanoic acid, pentylheptanoic acid, Tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyldodecanoic acid, propylundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid , methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, ethyltetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecane acid, heptylnonanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, nonylcyclohexanecarboxylic acid, etc. unsaturated fatty acids such as octenoic acid, nonenoic acid, methylnonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, and sabienic acid; Aromas such as acid, pyromellitic acid, o-phenoxybenzoic acid, methylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, butylbenzoic acid, pentylbenzoic acid, hexylbenzoic acid, heptylbenzoic acid, octylbenzoic acid, nonylbenzoic acid group carboxylic acids. An organic acid may be used individually by 1 type, and may be used in combination of 2 or more type. By combining such an organic acid with the first copper particles, there is a tendency that both the dispersibility of the first copper particles and the detachability of the organic acid during sintering can be achieved.

The treatment amount of the surface treatment agent may be an amount equal to or greater than one molecular layer on the particle surface. The treatment amount of such a surface treatment agent varies depending on the specific surface area of the first copper particles, the molecular weight of the surface treatment agent, and the minimum coverage area of the surface treatment agent. The treatment amount of the surface treatment agent is usually 0.001% by mass or more based on the total mass of the first copper particles after the surface treatment. The specific surface area of the first copper particles, the molecular weight of the surface treatment agent, and the minimum coverage area of the surface treatment agent can be calculated by methods described later.

Examples of commercially available materials containing the first copper particles include MA-C025 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle diameter 7.5 μm, average maximum diameter 4.1 μm), 3L3 (Fukuda Metal Foil Powder Kogyo Co., Ltd., volume average particle diameter 8.0 μm, average maximum diameter 7.3 μm), 2L3 (Fukuda Metal Foil & Powder Co., Ltd., volume average particle diameter 9.9 μm, average maximum diameter 9 μm), 2L3N / A ( Fukuda Metal Foil & Powder Co., Ltd., volume average particle diameter 9.4 μm, average maximum diameter 9 μm), 1110F (Mitsui Kinzoku Co., Ltd., volume average particle diameter 3.8 μm, average maximum diameter 5 μm), HWQ 3.0 μm ( Fukuda Metal Foil & Powder Co., Ltd., volume average particle diameter 3.0 μm), 2L3N (Fukuda Metal Foil & Powder Industry Co., Ltd., volume average particle diameter 7.2 μm), 3L3N (Fukuda Metal Foil & Powder Industry Co., Ltd., volume average particle diameter average particle diameter 5.9 μm), 4L3 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle diameter 4.5 μm), and C3 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle diameter 40.0 μm). .

The content of the first copper particles may be 10 to 70% by mass, 10 to 50% by mass, or 15 to 45% by mass, based on the total mass of the metal particles. , 20 to 40% by mass. If the content of the first copper particles is within the above range, it becomes easy to ensure the bonding strength of the bonded body manufactured by sintering the metal paste, and when the metal paste is used to bond semiconductor elements. tend to show better die shear strength and connection reliability in semiconductor devices. The above content does not include the amount of the surface treatment agent. Also, the total mass of the metal particles does not include the amount of the surface treatment agent adsorbed on the surfaces of the metal particles.

[Second copper particles]
The second copper particles preferably contain copper particles having a particle size of 0.12 to 0.8 μm. The second copper particles can contain, for example, 10% by mass or more of copper particles having a particle size of 0.12 to 0.8 μm. The content of copper particles having a particle size of 0.12 to 0.8 μm in the second copper particles is 20% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, from the viewpoint of sinterability of the metal paste. It may be at least 80% by mass, at least 90% by mass, or at least 100% by mass. That is, the second copper particles may be copper particles having a particle size of 0.12 to 0.8 μm. When the content of the copper particles having a particle size of 0.12 to 0.8 μm in the second copper particles is 20% by mass or more, the dispersibility of the copper particles is further improved, the viscosity is increased, and the paste concentration is reduced. can be suppressed more.

The volume average particle size of the second copper particles is preferably 0.10 μm or more and preferably 0.8 μm or less. If the volume average particle diameter of the second copper particles is 0.10 μm or more, it is possible to reduce the expensive synthesis cost seen in bonding materials that mainly use copper nanoparticles. Moreover, the dispersibility can be improved, and a decrease in the amount of volume shrinkage after sintering can be suppressed. Furthermore, it becomes easy to obtain the effect of suppressing the amount of the surface treatment agent used. If the volume average particle size of the second copper particles is 0.8 μm or less, the effect of excellent sinterability of the metal paste is likely to be obtained. From the viewpoint of further achieving the above effects, the volume average particle diameter of the second copper particles may be 0.12 to 0.8 μm, may be 0.15 to 0.8 μm, or may be 0.15 ~0.6 μm, 0.2-0.5 μm, or 0.3-0.45 μm. From the above viewpoint, the content of copper nanoparticles (particles having a particle size of 1 to 100 nm) in the second copper particles is preferably 2% by mass or less, more preferably 1% by mass or less. The content of copper nanoparticles in the second copper particles may be 0.5% by mass or more.

The shape of the second copper particles is not particularly limited. The shape of the second copper particles includes, for example, spherical, massive, needle-like, flake-like, substantially spherical, and aggregates thereof. From the viewpoint of dispersibility and filling property, the shape of the second copper particles may be spherical, approximately spherical, or flaky. It may be spherical or substantially spherical from the viewpoint of miscibility with particles).

The aspect ratio of the second copper particles may be 5.0 or less from the viewpoint of dispersibility, filling properties, and mixing with flaky particles (e.g., flaky first copper particles), It may be 3.0 or less.

The second copper particles may be treated with a specific surface treatment agent. Specific surface treatment agents include, for example, organic acids having 8 or more carbon atoms (excluding monovalent carboxylic acids having 1 to 9 carbon atoms). Examples of organic acids having 8 or more carbon atoms include polyvalent carboxylic acids having 8 to 9 carbon atoms, the aforementioned carboxylic acids having 10 or more carbon atoms (monovalent and polyvalent carboxylic acids), and alkyl groups having 8 or more carbon atoms. Among these, carboxylic acids having 10 or more carbon atoms are preferred. In the present embodiment, there is a tendency that the carboxylic acid having 10 or more carbon atoms is desorbed during sintering. Therefore, when a carboxylic acid having 10 or more carbon atoms is used, the effect of the present invention can be remarkable.

Specific examples of such surface treatment agents include capric acid, methylnonanoic acid, ethyloctanoic acid, propylheptanoic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanoic acid, lauric acid, Methylundecanoic acid, ethyldecanoic acid, propylnonanoic acid, butyloctanoic acid, pentylheptanoic acid, tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyl Dodecanoic acid, propylundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid, methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanic acid , ethyltetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octyl Saturated fatty acids such as cyclohexanecarboxylic acid and nonylcyclohexanecarboxylic acid; Unsaturated fatty acids such as decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid and sabienic acid; acids, pyromellitic acid, o-phenoxybenzoic acid, propylbenzoic acid, butylbenzoic acid, pentylbenzoic acid, hexylbenzoic acid, heptylbenzoic acid, octylbenzoic acid, nonylbenzoic acid and other aromatic carboxylic acids. An organic acid may be used individually by 1 type, and may be used in combination of 2 or more type. By combining such an organic acid with the second copper particles, there is a tendency that both the dispersibility of the second copper particles and the detachability of the organic acid during sintering can be achieved.

The treatment amount of the surface treatment agent may be 0.07 to 2.1% by mass, and 0.10 to 1.6% by mass, based on the total mass of the second copper particles after surface treatment. may be 0.2 to 1.1% by mass.

The treatment amount of the surface treatment agent may be an amount that allows one to three molecular layers to adhere to the surface of the second copper particles. This throughput is measured by the following method. W1 (g) of the surface-treated second copper particles is weighed into an alumina crucible (for example, manufactured by AS ONE, model number: 1-7745-07) that has been treated at 700 ° C. for 2 hours in the air, and is placed in the air at 700 ° C. Bake for 1 hour. After that, it is treated in hydrogen at 300° C. for 1 hour, and the mass W2 (g) of the copper particles in the crucible is measured. Next, the treatment amount of the surface treatment agent is calculated based on the following formula.
Treatment amount of surface treatment agent (% by mass) = (W1-W2)/W1 x 100

The specific surface area of the second copper particles may be 0.5 m ² /g to 10 m ² /g, and 1.0 m ² /g to 8.0 m ² from the viewpoint of sinterability, packing between particles, etc. /g, or from 1.2 m ² /g to 6.5 m ² /g. The specific surface area of the second copper particles can be calculated by measuring the dried second copper particles by the BET specific surface area measurement method.

Examples of commercially available materials containing second copper particles include CH-0200 (Mitsui Kinzoku Co., Ltd., volume average particle size 0.36 μm), HT-14 (Mitsui Kinzoku Co., Ltd., volume average particle diameter 0.41 μm), CT-500 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle diameter 0.72 μm), and Tn-Cu100 (manufactured by Taiyo Nissan Co., Ltd., volume average particle diameter 0.12 μm).

The content of the second copper particles may be 30 to 90% by mass, may be 35 to 90% by mass, or may be 40 to 85% by mass or less, based on the total mass of the metal particles. It may be 45 to 80% by mass or less. If the content of the second copper particles is within the above range, it becomes easy to ensure the bonding strength of the bonded body manufactured by sintering the metal paste, and when the metal paste is used for bonding semiconductor elements, Semiconductor devices tend to exhibit good die shear strength and connection reliability. The above content does not include the amount of the surface treatment agent. Also, the total mass of the metal particles does not include the amount of the surface treatment agent adsorbed on the surfaces of the metal particles.

The content of the second copper particles is preferably 30 to 90% by mass based on the sum of the mass of the first copper particles and the mass of the second copper particles. If the content of the second copper particles is 30% by mass or more, the space between the first copper particles can be filled, and the bonding strength of the bonded body manufactured by sintering the metal paste can be secured. When the metal paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. If the content of the second copper particles is 90% by mass or less, the volume shrinkage when the metal paste is sintered can be sufficiently suppressed, so the joining strength of the joined body produced by sintering the metal paste When the metal paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of further achieving the above effects, the content of the second copper particles may be 35 to 85% by mass based on the total mass of the first copper particles and the second copper particles. , 40 to 85% by mass, or 45 to 80% by mass. The above content does not include the amount of the surface treatment agent. Also, the total mass of the metal particles does not include the amount of the surface treatment agent adsorbed on the surfaces of the metal particles.

The sum of the content of the first copper particles and the content of the second copper particles may be 80-100% by mass based on the total mass of the metal particles. If the sum of the content of the first copper particles and the content of the second copper particles is within the above range, the volume shrinkage when the metal paste is sintered can be sufficiently reduced, and the metal paste can be sintered. It becomes easy to ensure the bonding strength of the manufactured bonded body. When a metal paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of further achieving the above effects, the total content of the first copper particles and the content of the second copper particles may be 90% by mass or more based on the total mass of the metal particles, It may be 95% by mass or more, or may be 100% by mass. The above content does not include the amount of the surface treatment agent. Also, the total mass of the metal particles does not include the amount of the surface treatment agent adsorbed on the surfaces of the metal particles.

[Other metal particles other than copper particles]
Metal particles other than copper particles include at least one metal particle selected from the group consisting of zinc particles and silver particles. When such metal particles are mixed, the bonding strength tends to be improved, and particularly when the adherend is gold or silver, the bonding strength tends to be improved. The other metal particles may be treated with a surface treatment agent. The content of the other metal particles (for example, the sum of the content of zinc particles and the content of silver particles) is 0.01 based on the total mass of the metal particles from the viewpoint of further improving the adhesiveness. ~10% by mass is preferable, 0.05 to 5% by mass is more preferable, and 0.1 to 2% by mass is even more preferable. The volume average particle diameter of the other metal particles (for example, the volume average particle diameter of zinc particles and the volume average particle diameter of silver particles) may be 0.01 to 10 μm, or 0.01 to 5 μm. Well, it may be 0.05-3 μm. The shape of other metal particles is not particularly limited. The above content does not include the amount of the surface treatment agent. Also, the total mass of the metal particles does not include the amount of the surface treatment agent adsorbed on the surfaces of the metal particles.

(dispersion medium)
The dispersion medium includes at least a first dispersion medium and a second dispersion medium. The dispersion medium has a function of dispersing the metal particles.

[First dispersion medium]
The first dispersion medium is a volatile organic compound having a boiling point of 235° C. or less and a weight average molecular weight of 130-170.

The boiling point of the first dispersion medium is preferably 230°C or lower, more preferably 220°C or lower. From the viewpoint of improving production stability, the boiling point of the first dispersion medium is preferably 150° C. or higher, more preferably 200° C. or higher, and even more preferably 215° C. or higher.

The weight-average molecular weight of the first dispersion medium is preferably 140 or more, more preferably 150 or more, from the viewpoint of easily obtaining thixotropy and facilitating the orientation of the copper particles. The weight average molecular weight of the first dispersion medium is preferably 165 or less, more preferably 160 or less, from the viewpoint of facilitating the orientation of the copper particles without excessively increasing the viscosity. The weight average molecular weight of the first dispersion medium can be measured, for example, by gel permeation chromatography using polystyrene as a standard substance.

The viscosity of the first dispersion medium is preferably 5 mPa·s or more, more preferably 10 mPa·s or more, and still more preferably 30 mPa·s or more, from the viewpoint of facilitating dispersion of the metal particles. The viscosity of the first dispersion medium is preferably 150 mPa·s or less, more preferably 100 mPa·s or less, and even more preferably 80 mPa·s or less, from the viewpoint of facilitating coating or printing. The viscosity of the first dispersion medium can be measured by, for example, a tuning fork vibration viscometer.

Specific examples of the first dispersion medium include α-terpineol and butyl carbitol. Among these, it is easy to form a structure composed of first flake-shaped copper particles oriented substantially parallel to the bonding interface and second copper particles dispersed between the first flake-shaped copper particles, α-Terpineol is preferably used because it is easy to obtain the effect of improving the bonding strength.

The content of the first dispersion medium is preferably 2 parts by mass or more with respect to 100 parts by mass of the metal particles from the viewpoint of easily obtaining the effect of improving the bonding strength. The content of the first dispersion medium may be 4 parts by mass or more or 7 parts by mass or more with respect to 100 parts by mass of the metal particles. The content of the first dispersion medium is less likely to inhibit the sintering of the copper particles and more likely to suppress a decrease in the effect of improving the bonding strength due to volatilization of the dispersion medium. It is preferably 15 parts by mass or less. The content of the first dispersion medium may be 12 parts by mass or less or 10 parts by mass or less with respect to 100 parts by mass of the metal particles. From these viewpoints, the content of the first dispersion medium is, for example, 2 to 15 parts by mass, 4 to 12 parts by mass, 4 to 10 parts by mass, or 7 to 10 parts by mass with respect to 100 parts by mass of the metal particles. be.

(Second dispersion medium)
The weight average molecular weight of polyethylene glycol as the second dispersion medium is 200-600. Since the boiling point of polyethylene glycol having a weight-average molecular weight of 200 or higher is usually 250°C or higher, the second dispersion medium hardly volatilizes at a temperature of at least 200°C. For example, even if the bonding metal paste of the present embodiment is dried at 50 to 180° C. for 1 to 120 minutes, the second dispersion medium remains in the bonding metal paste. Therefore, the structure formed by the first copper particles and the second copper particles is maintained even in the sintering process. Moreover, since the melting point of polyethylene glycol having a weight average molecular weight of 600 or less is usually lower than room temperature (25° C.), good applicability can be obtained. Moreover, when the weight average molecular weight of polyethylene glycol is 600 or less, the boiling point does not become too high, and it is easy to remove when sintering the copper particles.

The weight-average molecular weight of polyethylene glycol is preferably 300 or more, more preferably 350 or more, and even more preferably 400 or more, from the viewpoint of further obtaining the effect of improving joint strength. The weight-average molecular weight of polyethylene glycol is preferably 500 or less, more preferably 450 or less, and still more preferably 400 or less from the viewpoint of obtaining a further effect of improving the bonding strength and obtaining better coating properties. be. From these viewpoints, the weight average molecular weight of polyethylene glycol is, for example, 200-600, 300-600, 300-500, 300-450, 300-400, 350-450 or 400-450. In particular, when the copper particles are sintered at 300° C. or lower, the weight average molecular weight of polyethylene glycol is preferably within the above range. Within such a range, polyethylene glycol residues are less likely to remain in the joint (sintered body of the metal paste), and there is a tendency to obtain more excellent joint strength.

Specific examples of the second dispersion medium include polyethylene glycol 200 (manufactured by Wako Pure Chemical Industries, Ltd., Wako first grade), polyethylene glycol 300 (manufactured by Wako Pure Chemical Industries, Ltd., Wako first grade), and polyethylene glycol 400. (manufactured by Wako Pure Chemical Industries, Ltd., Wako first grade), polyethylene glycol 600 (manufactured by Wako Pure Chemical Industries, Ltd., Wako first grade), and the like can be used. These may be used singly or in combination.

The content of the second dispersion medium is preferably 4 parts by mass or more with respect to 100 parts by mass of the metal particles, from the viewpoint of further obtaining the effect of improving the bonding strength. The content of the second dispersion medium may be 5 parts by mass or more, 6 parts by mass or more, or 9 parts by mass or more with respect to 100 parts by mass of the metal particles. The content of the second dispersion medium is preferably 14 parts by mass or less, more preferably 10 parts by mass or less with respect to 100 parts by mass of the metal particles, from the viewpoint of further obtaining the effect of improving the bonding strength. The content of the second dispersion medium may be 7 parts by mass or less with respect to 100 parts by mass of the metal particles. From these points of view, the content of the second dispersion medium is, for example, 4 to 14 parts by mass, 4 to 10 parts by mass, 4 to 7 parts by mass, 5 to 14 parts by mass with respect to 100 parts by mass of the metal particles, 5 to 10 parts by mass, 6 to 10 parts by mass, or 9 to 14 parts by mass.

A preferred range of the mass ratio r of the content of the second dispersion medium to the content of the first dispersion medium (content of the second dispersion medium/content of the first dispersion medium) is depending on the weight average molecular weight of When the second dispersion medium contains multiple polyethylene glycols with different weight average molecular weights, the weight average molecular weight of the second dispersion medium is the weight average molecular weight obtained by measuring a mixture of multiple polyethylene glycols. .

For example, when the weight average molecular weight of the second dispersion medium is 200 or more and less than 350, the mass ratio r is preferably 0.3 or more, more preferably 0.3 or more, more preferably 0.3 or more, from the viewpoint of further obtaining the effect of improving the bonding strength. 8 or more, more preferably 1.0 or more, particularly preferably 1.2 or more, and extremely preferably 2.0 or more. The mass ratio r is preferably 3.0 or less, more preferably 2.5 or less, from the viewpoint of further obtaining the effect of improving the bonding strength. From these points of view, the mass ratio r is, for example, 0.3-3.0, 0.8-3.0, 1.0-3.0, 1.0-2.5, 1.2-2. 5 or 2.0 to 2.5.

Further, for example, when the weight average molecular weight of the second dispersion medium is 350 or more and 450 or less, the mass ratio r is preferably 0.3 or more, more preferably 0.45 or more. The mass ratio r is preferably 3.0 or less, more preferably 2.5 or less, even more preferably 1.2 or less, and particularly preferably 0.85 or less, from the viewpoint of further improving the bonding strength. . From these points of view, the mass ratio of the content of the second dispersion medium to the content of the first dispersion medium is, for example, 0.3 to 3.0, 0.45 to 2.5, 0.45 to 1 .2 or 0.45 to 0.85.

Further, for example, when the weight average molecular weight of the second dispersion medium is more than 450 and 600 or less, the mass ratio r is preferably 0.3 or more, more preferably It is 0.45 or more, more preferably 0.8 or more, particularly preferably 1.2 or more, and most preferably 2.0 or more. The mass ratio r is preferably 3.0 or less, more preferably 2.5 or less, from the viewpoint of further obtaining the effect of improving the bonding strength. From these points of view, the mass ratio r is, for example, 0.3 to 3.0, 0.45 to 3.0, 0.8 to 3.0, 1.2 to 3.0 or 2.0 to 2.0. 5.

The content of the dispersion medium (for example, the sum of the content of the first dispersion medium and the content of the second dispersion medium) may be 2 to 50% by mass based on the total mass of the bonding metal paste, It may be 5 to 30% by mass, 5 to 20% by mass, or 5 to 12% by mass. Also, the content of the dispersion medium may be 5 to 50 parts by mass, with the total mass of the metal particles being 100 parts by mass. If the content of the dispersion medium is within the above range, the metal paste for bonding can be adjusted to have a more appropriate viscosity, and the sintering of the copper particles is less likely to be inhibited.

(Surface treatment agent)
The above surface treatment agent (for example, carboxylic acid having 10 or more carbon atoms) may be adsorbed to the metal particles by hydrogen bonding or the like, or may be free or dispersed in the paste (for example, in the dispersion medium). The content of the surface treatment agent may be 0.07 to 2.1 parts by mass, 0.10 to 1.6 parts by mass, or 0.2 to 1.6 parts by mass with respect to 100 parts by mass of the metal particles. It may be 1.1 parts by mass. The components described above as the surface treatment agent do not necessarily need to be contained for the purpose of surface treatment of the metal particles, and may be contained in the metal paste for purposes other than surface treatment (for example, as a dispersion medium). .

(other ingredients)
The metal paste may contain, for example, additives as components other than the components described above. Examples of additives include wettability improvers such as nonionic surfactants and fluorosurfactants; antifoaming agents such as silicone oil; ion trapping agents such as inorganic ion exchangers. The content of the additive can be adjusted as appropriate within a range that does not impair the effects of the present invention.

The viscosity of the metal paste described above is not particularly limited, and in the case of molding by means of printing, coating, or the like, the viscosity may be adjusted to suit the molding method. The metal paste may have, for example, a Casson viscosity at 25° C. of 0.05 Pa·s or more and 2.0 Pa·s or less, or 0.06 Pa·s or more and 1.0 Pa·s or less.

The metal paste is preferably stored below 30°C. If the paste is stored at 30° C. or higher, the monovalent carboxylic acid having 1 to 10 carbon atoms and optionally the dispersing medium may easily volatilize, which may change the concentration of the metal paste. As a result, when disposing the metal paste on the member, it may be difficult to dispose it on a desired portion. The metal paste may be stored frozen (eg −30° C.) or at temperatures below that. However, since it is preferable to use the metal paste at room temperature (for example, 10 to 30°C), if it is stored at less than -30°C, it takes time to thaw, and heating is required for thawing, which increases the process cost. Connect.

It is preferable that the change in volume average particle size of the metal paste is within 20% before and after storage. When the copper particles (for example, the second copper particles) forming the metal paste agglomerate in the metal paste to form secondary particles, the volume average particle size increases. If the volume-average particle size becomes large, voids are likely to form after sintering, and the thermal conductivity may decrease. In addition, the voids become stress concentration points and cracks are likely to occur, making it difficult to obtain desired performance (for example, performance evaluated in a temperature cycle test and a power cycle test).

<Preparation of metal paste>
The metal paste described above includes copper particles (first copper particles and second copper particles), a dispersion medium (first dispersion medium and second dispersion medium), and optionally other components (other metal particles, additives, etc.). After mixing each component, a stirring treatment may be performed. The metal paste may be classified to adjust the maximum particle size of the dispersion. At this time, the maximum particle size of the dispersion can be 20 μm or less, and can be 10 μm or less.

The metal paste is obtained by pre-mixing the second copper particles, the first dispersion medium, and, if necessary, a surface treatment agent (for example, an organic acid having 8 or more carbon atoms), and performing a dispersion treatment to form the second may be prepared by preparing a dispersion of copper particles, further mixing the first copper particles, other metal particles and additives, and finally adding and mixing the second dispersion medium. By adopting such a procedure, for example, the dispersibility of the second copper particles is improved, the mixing property with the first copper particles is improved, and the performance of the metal paste is further improved. Further, aggregates may be removed from the dispersion of the second copper particles by a classification operation.

The stirring treatment can be performed using a stirrer. The stirrer includes, for example, a rotation-revolution stirrer, a Raikai machine, a Hibis Dispermix, a twin-screw kneader, a three-roll mill, a planetary mixer, and a thin-layer shearing disperser.

The classification operation can be performed using, for example, filtration, natural sedimentation, centrifugation, or the like. Examples of filters for filtration include metal meshes, metal filters, nylon meshes, and the like.

Dispersion treatment includes, for example, a thin-layer shearing disperser, disperser, bead mill, Hivis Dispermix, ultrasonic homogenizer, high shear mixer, narrow gap three-roll mill, wet ultra-atomizing device, supersonic jet mill, and ultra-high pressure. A homogenizer etc. are mentioned.

<Joint body>
A bonded body (for example, a semiconductor device) according to the present embodiment will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted. Also, the dimensional ratios in the drawings are not limited to the illustrated ratios.

FIG. 1 is a schematic cross-sectional view showing an example of a joined body manufactured using the metal paste of this embodiment.

A joined body 100 shown in FIG. And prepare.

Examples of the first member 2 and the second member 3 include semiconductor elements such as IGBTs, diodes, Schottky barrier diodes, MOS-FETs, thyristors, logic, sensors, analog integrated circuits, LEDs, semiconductor lasers, and oscillators. , lead frames, metal plate bonded ceramic substrates (e.g. DBC), substrates for mounting semiconductor devices such as LED packages, metal wiring such as copper ribbons and metal frames, block bodies such as metal blocks, power supply members such as terminals, heat dissipation plates, water-cooled plates, and the like.

The surfaces 2a and 3a of the first member 2 and the second member 3 that are in contact with the metal paste sintered body 1 may contain metal. Examples of metals include copper, nickel, silver, gold, palladium, platinum, lead, tin and cobalt. A metal may be used individually by 1 type, and may be used in combination of 2 or more type. Also, the surface in contact with the sintered body may be an alloy containing the above metals. Metals used for the alloy include zinc, manganese, aluminum, beryllium, titanium, chromium, iron, molybdenum, etc., in addition to the above metals. Examples of members containing metal on the surface in contact with the sintered body include members having various metal platings (chips having metal plating, lead frames having various metal platings, etc.), wires, heat spreaders, and metal plates attached. Examples include ceramic substrates, lead frames made of various metals, copper plates, and copper foils.

The die shear strength of the bonded body 100 may be 10 MPa or more, 15 MPa or more, or 20 MPa or more from the viewpoint of sufficiently bonding the first member 2 and the second member 3. It may be 25 MPa or more. The die shear strength can be measured using a universal bond tester (Royce 650, manufactured by Royce Instruments).

The thermal conductivity of the metal paste sintered body 1 may be 100 W/(mK) or more, and may be 120 W/(mK) or more, from the viewpoint of heat dissipation and connection reliability at high temperatures. may be 150 W/(m·K) or more. The thermal conductivity can be calculated from the thermal diffusivity, specific heat capacity, and density of the sintered metal paste.

In the bonded body 100, when the first member 2 is a semiconductor element, the bonded body 100 becomes a semiconductor device. The resulting semiconductor device can have sufficient die shear strength and connection reliability.

FIG. 2 is a schematic cross-sectional view showing an example of a semiconductor device manufactured using the metal paste of this embodiment. The semiconductor device 110 shown in FIG. 2 is connected to the lead frame 15a through the sintered body 11 of the metal paste according to the present embodiment, the lead frame 15a, the lead frame 15b, the wire 16, and the sintered body 11. and a mold resin 17 for molding them. Semiconductor element 18 is connected to lead frame 15b via wire 16 .

Semiconductor devices manufactured using the metal paste of the present embodiment include, for example, power modules such as diodes, rectifiers, thyristors, MOS gate drivers, power switches, power MOSFETs, IGBTs, Schottky diodes, fast recovery diodes, oscillators, etc. machines, amplifiers, high-brightness LED modules, sensors, etc.

<Method for manufacturing joined body>
A method for manufacturing a bonded body 100 (for example, a semiconductor device 110) using the metal paste of this embodiment will be described below.

The method for manufacturing the joined body 100 according to the present embodiment is a lamination in which the first member 2, the metal paste, and the second member 3 are laminated in this order on the side in which the weight of the first member 2 acts. A body is prepared, and the metal paste is sintered at 300 ° C. or less under the weight of the first member 2 or under the weight of the first member 2 and a pressure of 0.01 MPa or less. It has a process to do. The direction in which the weight of the first member 2 acts can also be said to be the direction in which gravity acts.

The laminate can be prepared, for example, by applying the metal paste of the present embodiment to a necessary portion of the first member 2 or the second member 3, and then arranging the members to be joined on the metal paste. .

As a method for providing the metal paste of the present embodiment on the necessary portions of the first member and the second member, any method that allows the metal paste to be deposited may be used. Examples of such methods include printing methods such as screen printing, transfer printing, offset printing, letterpress printing, intaglio printing, gravure printing, stencil printing, and jet printing, dispensers (eg, jet dispensers, needle dispensers), and comma coaters. , a method using a slit coater, a die coater, a gravure coater, a slit coater, a bar coater, an applicator, a spray coater, a spin coater, a dip coater, a method using soft lithography, a particle deposition method, a method using electrodeposition coating, and the like.

The thickness of the metal paste may be 1-1000 μm, 10-500 μm, 50-200 μm, 10-3000 μm, or 15-500 μm. , 20-300 μm, 5-500 μm, 10-250 μm, or 15-150 μm.

The metal paste provided on the member may be dried as appropriate from the viewpoint of suppressing flow and generation of voids during sintering. The gas atmosphere at the time of drying may be the atmosphere, an oxygen-free atmosphere such as nitrogen or rare gas, or a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying by standing at room temperature, drying by heating, or drying under reduced pressure. For heat drying or reduced pressure drying, for example, hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic A heating device, a heater heating device, a steam heating furnace, a hot plate press device, or the like can be used. The drying temperature and time may be appropriately adjusted according to the type and amount of the volatile component (eg, dispersion medium) used. The drying temperature and time may be, for example, 50 to 180° C. for 1 to 120 minutes. Further, for example, the metal paste provided on the member may be dried, for example, at 15° C. to 50° C. for 1 to 120 minutes in terms of the production process.

As a method of placing one member on the other member (for example, a method of placing the first member on a second member provided with a metal paste), for example, a chip mounter, a flip chip bonder, a carbon Alternatively, a ceramic positioning jig or the like may be used.

The metal paste is sintered by heat-treating the laminate. For heat treatment, for example, hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic heating device, A heater heating device, a steam heating furnace, or the like can be used.

The gas atmosphere during sintering may be an oxygen-free atmosphere from the viewpoint of suppressing oxidation of the sintered body and members (the first member and the second member). The gas atmosphere during sintering may be a reducing atmosphere from the viewpoint of removing the surface oxides of the copper particles in the metal paste. The oxygen-free atmosphere includes, for example, an oxygen-free gas atmosphere such as nitrogen or rare gas, or a vacuum. Examples of the reducing atmosphere include a pure hydrogen gas atmosphere, a mixed gas atmosphere of hydrogen and nitrogen represented by forming gas, a nitrogen atmosphere containing formic acid gas, a mixed gas atmosphere of hydrogen and a rare gas, a rare gas atmosphere containing formic acid gas, and the like. is mentioned.

The temperature (maximum temperature reached) during the heat treatment may be 170 to 300° C. from the viewpoint of reducing thermal damage to the members (the first member and the second member) and improving the yield. It may be 200° C. or more and less than 300° C., it may be 200 to 275° C., it may be 225° C. or more and less than 275° C., it may be 250 to 275° C., or it may be 250° C. or more and less than 275° C. may be

In the present embodiment, the temperature (maximum temperature reached) during heat treatment is preferably 300° C. or less, but for the purpose of improving reliability in reliability tests such as temperature cycle tests and power cycle tests, the temperature is 301° C. or more. Heat treatment can also be performed under conditions of 400° C. or less.

The reaching maximum temperature holding time may be 1 to 120 minutes from the viewpoint of volatilizing all the volatile components (eg, the first dispersion medium and the second dispersion medium) and improving the yield, and 1 to 60 minutes. , 1 minute or more and less than 40 minutes, or 1 minute or more and less than 30 minutes.

By using the metal paste of the present embodiment, when sintering the laminate, the bonded body can have sufficient bonding strength even when bonding is performed without pressure. That is, only the weight of the first member laminated on the metal paste, or in addition to the weight of the first member, under pressure of 0.01 MPa or less, preferably 0.005 MPa or less, sufficient bonding strength can be obtained. If the pressure received during sintering is within the above range, a special pressurizing device is not required, and void reduction, die shear strength, and connection reliability can be further improved without impairing yield. As a method for applying a pressure of 0.01 MPa or less to the metal paste, for example, a method of placing a weight on a member (for example, the first member) arranged vertically upward can be used.

When at least one of the first member and the second member is a semiconductor element, that is, when the bonded body 100 is the semiconductor device 110, it can be manufactured by the method described above. In this case, for example, a metal paste is provided on the lead frame 15a, and then the semiconductor element 18 is arranged on the metal paste. The resulting semiconductor device can have sufficient die shear strength and connection reliability even when bonding is performed without pressure. The semiconductor device of the present embodiment has sufficient bonding strength and has sufficient die shear strength and excellent connection reliability by being provided with a sintered body of metal paste containing copper with high thermal conductivity and melting point. At the same time, it can be excellent in power cycle resistance.

An example of the bonded body manufactured using the metal paste of the present embodiment has been described above, but the bonded body manufactured using the metal paste of the present embodiment is not limited to the above embodiment. A joined body manufactured using the metal paste of the present embodiment may be, for example, the joined bodies shown in FIGS.

A joined body 120 shown in FIG. The sintered body 1a of the metal paste to be joined, the sintered body 1b of the metal paste to join the first member 2 and the third member 4, the third member 4 and the fourth member 5 and a sintered body 1c of the metal paste to be joined.

Such a bonded body 120 includes, for example, the third member 4, the second metal paste, the first member 2, the first metal paste, and the second metal paste on the side in which the weight of the third member 4 acts. A laminated portion in which the second member 3 is laminated in this order, a third member 4, and a third metal paste and a fourth member 5 are laminated in this order on the side in which the weight of the third member 4 acts. A method comprising a step of preparing a laminate having a laminated portion and sintering the first metal paste, the second metal paste, and the third metal paste in the same manner as in the method for manufacturing the joined body 100 Obtainable. In the above method, the first metal paste, the second metal paste, and the third metal paste are the metal pastes according to the present embodiment, and the sintered body 1a is obtained by sintering the first metal paste. , the sintered body 1b is obtained by sintering the second metal paste, and the sintered body 1c is obtained by sintering the third metal paste.

In addition, for example, after the bonded body 100 is obtained, the bonded body 120 includes the third member 4, the second metal paste, and the first member 2 on the side in which the weight of the third member 4 acts. is laminated in this order, a third member 4, a laminated part in which a third metal paste and a fourth member 5 are laminated in this order on the side in which the weight of the third member 4 acts. and sintering the second metal paste and the third metal paste in the same manner as in the manufacturing method of the joined body 100.

A joined body 130 shown in FIG. 4 includes a first member 2, a second member 3, a third member 4, a fourth member 5, a fifth member 6, and a first member A sintered body 1a of the metal paste that joins the second member 3, a sintered body 1c of the metal paste that joins the third member 4 and the fourth member 5, and the first member 2 A sintered body 1d of the metal paste that joins the fifth member 6 and a sintered body 1e of the metal paste that joins the third member 4 and the fifth member 6 are provided.

Such a bonded body 130 includes the third member 4, the fifth metal paste, the fifth member 6, the fourth metal paste, the first member on the side in which the weight of the third member 4 acts. 2, a laminated portion in which the first metal paste and the second member 3 are laminated in this order, a third member 4, a third metal paste on the side in which the weight of the third member 4 acts, A laminate having a laminated portion in which the fourth member 5 is laminated in this order is prepared, and the first metal paste, the third metal paste, and the fourth metal are prepared in the same manner as in the manufacturing method of the joined body 100. It can be obtained by a method comprising a step of sintering a paste and a fifth metal paste. In the above method, the first metal paste, the third metal paste, the fourth metal paste, and the fifth metal paste are the metal pastes according to the present embodiment, and the first metal paste is sintered to sinter the metal paste. A sintered body 1c is obtained by sintering the third metal paste, a sintered body 1d is obtained by sintering the fourth metal paste, and a fifth metal paste is obtained. is sintered to obtain a sintered body 1e.

In addition, the bonded body 130 includes the third member 4, the fifth metal paste, the fifth member 6, the fourth metal paste, the first member 2, the third member 4, the fifth member 6, the fourth metal paste, and the first member 2 on the side in which the weight of the third member 4 acts. , the first metal paste, and the second member 3 are laminated in this order, and the first metal paste, the fourth metal paste, and the second After the five metal pastes are sintered, the third member 4, the laminated portion in which the third metal paste and the fourth member 5 are laminated in this order on the side in which the weight of the third member 4 acts. It can also be obtained by a method including a step of forming and sintering a third metal paste in the same manner as in the method of manufacturing the bonded body 100 described above.

After the joined body 100 is obtained, the joined body 130 includes the third member 4, the fifth metal paste, the fifth member 6 and the fourth metal paste in the direction in which the weight of the third member 4 acts. A laminated portion in which the metal paste of the first member 2 is laminated in this order, a third member 4, a third metal paste, a fourth member 5 on the side in which the weight of the third member 4 acts. are laminated in this order, and sintering the third metal paste, the fourth metal paste, and the fifth metal paste in the same manner as in the method for manufacturing the joined body 100. can also be obtained with

In the modified example, examples of the third member 4, the fourth member 5 and the fifth member 6 are the same as the example of the second member. Further, the surfaces of the third member 4, the fourth member 5 and the fifth member 6, which are in contact with the sintered body of the metal paste, may contain metal. Examples of the metal that can be contained are the same as those of the metal that can be contained in the surfaces of the first member 2 and the second member 3 in contact with the sintered body of the metal paste. Moreover, the first metal paste, the second metal paste, the third metal paste, the fourth metal paste, and the fifth metal paste used in the modified examples may be the same or different.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Preparation of materials>
The following materials were prepared.

[Metal particles]
・ CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd., shape: pseudospherical, surface treatment agent: lauric acid (dodecanoic acid), surface treatment amount: 0.973% by mass (based on the total mass of CH-0200), 50% volume Average particle diameter: 0.36 μm, content of copper particles having a particle diameter of 0.1 μm or more and less than 1 μm: 100% by mass, content of copper particles having a particle diameter of 0.12 μm or more and 0.8 μm or less: 100 mass %)
・ 2L3N / A (manufactured by Fukuda Metal Foil & Powder Co., Ltd., shape: flake, surface treatment amount: 0.8% by mass (based on the total mass of 2L3N / A), 50% volume average particle size: 9.4 μm, BET Specific surface area: 13400 cm ² /g, aspect ratio: 5.25, content of copper particles with a maximum diameter of 2 to 50 μm: 100% by mass)
・ Zinc particles (product number: 13789, manufactured by Alfa Aesar)

[First dispersion medium]
・α-terpineol (manufactured by Wako Pure Chemical Industries, Ltd.)

[Second dispersion medium]
- Polyethylene glycol 200 (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight: 200)
- Polyethylene glycol 300 (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight: 300)
- Polyethylene glycol 400 (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight: 400)
- Polyethylene glycol 600 (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight: 600)

(Example 1)
<Preparation of Metal Paste 1>
α-Terpineol (first dispersion medium) 0.5 g, polyethylene glycol 200 (second dispersion medium) 0.6 g, CH-0200 2.86 g, and 2L3N / A 1.53 g were added to an agate mortar and dried powder. The mixture was kneaded until there was no liquid left, and the mixture was transferred to a plastic bottle. The sealed plastic bottle was stirred for 2 minutes at 2000 min ⁻¹ (2000 rpm) using a rotation-revolution stirrer (Planetary Vacuum Mixer ARV-310, manufactured by Thinky Corporation). After that, the resulting mixture and 0.009 g of zinc particles were added to an agate mortar and kneaded until no dry powder remained, and the mixture was transferred to a plastic bottle. The sealed plastic bottle was stirred for 2 minutes at 2000 min ⁻¹ (2000 rpm) using a rotation-revolution stirrer (Planetary Vacuum Mixer ARV-310, manufactured by Thinky Corporation). The obtained paste-like mixed liquid was designated as metal paste 1. Table 1 shows the content of the first dispersion medium and the content of the second dispersion medium based on 100 parts by mass of the metal particles, and the content of the second dispersion medium with respect to the content of the first dispersion medium. ("second dispersion medium/first dispersion medium" in Table 1).

<Production of joined body>
Using metal paste 1, a joined body of Example 1 was produced according to the following method.
First, a stainless steel metal mask (thickness: 100 μm) having 3 mm × 3 mm square openings in 3 rows and 3 columns was placed on a 19 mm × 25 mm electrolytic nickel-plated copper plate (total thickness: 3 mm, plating thickness: 3 to 5 μm). ), and the metal paste 1 was applied onto the copper plate by stencil printing using a metal squeegee. Next, a 3 mm×3 mm silicon chip (thickness: 400 μm) was prepared by sputtering titanium and nickel in this order, and nickel was placed on the applied metal paste so that the nickel was in contact with the metal paste. The silicon chip was placed. The silicon chip was brought into close contact with the metal paste by lightly pressing with tweezers. As a result, a laminate was obtained in which the copper plate, the metal paste 1 and the silicon chip were laminated in this order.

The obtained laminate was fired by the following method to obtain a joined body A and a joined body B. First, the laminate was set in a tube furnace (manufactured by ABC Co., Ltd.), and argon gas was flowed into the tube furnace at 3 L/min to replace the air in the tube furnace with argon gas. Thereafter, the temperature of the tube furnace was raised to 200° C. over 30 minutes while flowing hydrogen gas into the tube furnace at 500 ml/min. After the temperature was raised, sintering was performed under the conditions of a maximum maximum temperature of 300°C (measured on an electrolytic nickel-plated copper plate) and a maximum maximum temperature holding time of 60 minutes, and the nickel-plated copper plate and nickel-sputtered silicon A bonded body in which the chip was bonded was obtained. After sintering, the flow rate of argon gas was changed to 0.3 L/min to cool, and the joined body was taken out into the air at 50° C. or lower. By the above operation, the metal paste 1 was sintered without pressurization, and the joined body A of Example 1 was obtained. A joined body B of Example 1 was obtained in the same manner as in the joined body A except that the laminated body obtained above was heated on a hot plate heated to 90° C. for 2 hours and then baked. .

(Examples 2 to 15)
A paste mixture was prepared in the same manner as in Example 1, except that the amount of the first dispersion medium used and the type and amount of the second dispersion medium used were changed to the values shown in Tables 1 to 3. were prepared to obtain metal pastes 2 to 15, respectively. Next, joined bodies A and B of Examples 2 to 15 were produced in the same manner as in Example 1, except that metal pastes 2 to 15 prepared above were used instead of metal paste 1.

(Comparative example 1)
A paste mixture was prepared in the same manner as in Example 1 except that the second dispersion medium was not used and the amount of the first dispersion medium used was changed to the value shown in Table 3, A metal paste 16 was obtained. Next, joined bodies A and B of Comparative Example 1 were produced in the same manner as in Example 1, except that Metal Paste 16 was used instead of Metal Paste 1.

(Comparative example 2)
A paste mixture was prepared in the same manner as in Example 1 except that the first dispersion medium was not used and the amount of the second dispersion medium used was changed to the value shown in Table 3, A metal paste 17 was obtained. The obtained metal paste 17 had a high viscosity and was significantly inferior in coatability.

<Evaluation>
The die shear strengths of joined bodies A and B were measured according to the following procedure. The results are shown in Tables 1-3.

(Measurement of die shear strength)
The bonding strength of bonded bodies A and B was evaluated by die shear strength. Using a universal bond tester (Royce 650, manufactured by Royce Instruments) equipped with a load cell (SMS-200K-24200, manufactured by Royce Instruments), the silicon chip of the bonded body was measured horizontally at a measurement speed of 5 mm / min and a measurement height of 50 μm. Then, the die shear strength of the joined body was measured. The die shear strength was measured for each of eight bonded bodies A and B, and the average value of the values obtained by measuring the eight bonded bodies was taken as the die shear strength of the bonded body (bonded body A and bonded body B). and

DESCRIPTION OF SYMBOLS 1, 11... Sintered body of metal paste for joining 2... First member 3... Second member 15a, 15b... Lead frame 16... Wire 17... Mold resin 18... Semiconductor element 100... Bonded body 110 Semiconductor device 2a Surface in contact with the sintered body of the metal paste for bonding of the first member 3a Surface in contact with the sintered body of the metal paste for bonding of the second member.

Claims (11)

containing metal particles and a dispersion medium for dispersing the metal particles,
The metal particles include first flake-shaped copper particles having a particle size of 2 μm or more and second copper particles having a particle size of 0.8 μm or less,
A metal paste for bonding, wherein the dispersion medium contains α-terpineol as a first dispersion medium and polyethylene glycol having a weight average molecular weight of 200 to 600 as a second dispersion medium. 2. The joining metal paste according to claim 1, wherein said dispersion medium contains polyethylene glycol having a weight average molecular weight of 350 to 450 as said second dispersion medium. 3. The bonding metal paste according to claim 1, wherein the content of said second dispersion medium is 4 to 14 parts by mass with respect to 100 parts by mass of said metal particles. The metal paste for bonding according to any one of claims 1 to 3, wherein the content of the first dispersion medium is 2 to 15 parts by mass with respect to 100 parts by mass of the metal particles. The bonding metal according to any one of claims 1 to 4, wherein the mass ratio of the content of the second dispersion medium to the content of the first dispersion medium is 0.3 to 3.0. paste. The metal paste for bonding according to any one of claims 1 to 5, wherein the first copper particles have an aspect ratio of 3.0 or more. The first copper particles contain 50% by mass or more of copper particles having a particle size of 2 to 50 μm,
The metal paste for bonding according to any one of claims 1 to 6, wherein the second copper particles contain 20% by mass or more of copper particles having a particle size of 0.12 to 0.8 µm. The content of the first copper particles is 10 to 70% by mass based on the total mass of the metal particles,
The metal paste for bonding according to any one of claims 1 to 7, wherein the content of the second copper particles is 30 to 90 mass% based on the total mass of the metal particles. The metal particles further contain at least one metal particle selected from the group consisting of zinc particles and silver particles in an amount of 0.01 to 10% by mass based on the total mass of the metal particles. The metal paste for bonding according to any one of 1 to 8. A laminate in which a first member, the bonding metal paste according to any one of claims 1 to 9, and a second member are laminated in this order is prepared, and the bonding metal paste is applied to the second member. A method of manufacturing a joined body, comprising a step of sintering at 300° C. or less under the weight of one member or under the weight of the first member and a pressure of 0.01 MPa or less. 11. The method of manufacturing a joined body according to claim 10, wherein at least one of said first member and said second member is a semiconductor element.

Images