JP7629685B2 - Joining materials and articles - Google Patents

Description

The present invention relates to a bonding material and an article bonded with the bonding material.

Conventionally, solder has been used as a bonding material for bonding metal members together, between a metal member and a semiconductor element, or between a metal member and an LED element. In the field of next-generation power electronics, a lead-free alternative to solder is required as a bonding agent for devices such as SiC that can operate at high temperatures, from the environmental consideration aspect, and a bonding material using silver nanoparticles has been proposed. In general, metal nanoparticles, typified by silver nanoparticles, have their particle surfaces coated with an organic substance for stabilization, and when the coating material volatilizes and/or decomposes during sintering, the metal nanoparticles are sintered together to form a strong metal film.
As an example of a bonding material using such silver nanoparticles, Patent Document 1 describes a silver nano bonding paste containing a sintering accelerator, which has excellent coating suitability and bonding strength before and after thermal cycles. Patent Document 2 describes a bonding material containing a specific amount of silver fine particles and silver particles with an average primary particle size of nm size and a specific sintering aid, which can suppress the generation of unsintered parts.

JP 2018-172728 A JP 2015-225842 A

However, the bonding materials described in Patent Documents 1 and 2 are unable to solve the problems of bonding strength, particularly thermal shock resistance such as thermal cycle resistance.
Regarding the above, it is believed that the joining paste described in Patent Document 1 has an insufficient design of the boiling points of the coating material that coats the metal particles and the solvent, and the gas generated by the evaporation and/or decomposition of the coating material is not smoothly discharged to the outside of the film, but remains inside the film and forms voids (air gaps).
Regarding the above, in the bonding material described in Patent Document 2, one metal particle is coated with a kind of fatty acid, so that the metal particle coated with the coating material having a low boiling point starts sintering first, and after the coating film hardens, the other metal particle coated with the coating material having a high boiling point sinters, so that the gas cannot be discharged smoothly and many voids are formed inside the film.
The formation of voids causes problems such as weakening of the film, lowering of the bonding strength due to a reduction in the contact area with the substrate, and a significant deterioration in thermal shock resistance.

The objective of the present invention is therefore to provide a bonding material that has sinterability at a relatively low temperature of about 300°C and can form a sintered film that has excellent bonding strength before and after thermal cycles, and an article that uses the bonding material.

As a result of extensive research into solving the above problems, we discovered that the above problems could be solved by the embodiment shown below, and thus completed the present invention.

An embodiment of the present invention relates to a bonding material that includes metal particles coated with a fatty acid and an organic solvent, in which the fatty acid includes fatty acid A having 4 to 8 carbon atoms and fatty acid B having 14 to 20 carbon atoms, and the organic solvent includes organic solvent C having a boiling point of 170°C to 230°C and organic solvent D having a boiling point of 300°C to 350°C.

Another embodiment of the present invention relates to the above bonding material in which the molar ratio of fatty acid A and fatty acid B (moles of fatty acid A/moles of fatty acid B) is 0.5 to 30.

Another embodiment of the present invention relates to the above bonding material in which the mass ratio of organic solvent C to organic solvent D (mass of organic solvent C/mass of organic solvent D) is 1 to 3.

Another embodiment of the present invention relates to the above bonding material, in which the boiling point of fatty acid A is a temperature within ±0 to ±20°C of the boiling point of organic solvent C.

Another embodiment of the present invention relates to the above bonding material, in which the boiling point of fatty acid B is a temperature within ±0 to ±50°C of the boiling point of organic solvent D.

Another embodiment of the present invention relates to the above-mentioned bonding material, in which the metal particles are a reduced product of a silver compound using a carbodihydrazide represented by the following formula (1) or a polybasic acid polyhydrazide represented by the following formula (2).

［式（２）中、Ｒはｎ価の多塩基酸残基を表す。］

[In formula (2), R represents an n-valent polybasic acid residue.]

Another embodiment of the present invention relates to an article in which metal members are joined together, a metal member and a semiconductor element, or a metal member and an LED element are joined together with a sintered body formed from the above-mentioned joining material.

The present invention provides a bonding material that can be sintered at a relatively low temperature of about 300°C and can form a sintered film that has excellent bonding strength before and after thermal cycles, as well as an article that uses the bonding material.

The bonding material of the present invention is characterized in that it contains metal particles coated with a fatty acid, the fatty acid including fatty acid A having 4 to 8 carbon atoms and fatty acid B having 14 to 20 carbon atoms, organic solvent C having a boiling point of 170° C. or more and 230° C. or less, and organic solvent D having a boiling point of 300° C. or more and 350° C. or less.
As a result of extensive research, the applicant has found that in order for volatile components such as fatty acids in the bonding material to be smoothly released to the outside of the film, it is important that the bonding material has a low viscosity during sintering and that the fatty acids volatilize together with the solvent components. The applicant has found that by combining two types of fatty acids having specific carbon numbers with two types of organic solvents having specific boiling points, it is possible to form a sintered body that exhibits excellent low-temperature sintering properties and thermal shock resistance while maintaining the stability of the bonding material, and that has excellent bonding strength before and after thermal cycles.
The present invention will be described in detail below.

<Metal Particles>
The bonding material of the present invention includes metal particles coated with a specific fatty acid. Examples of the metal particles include metal powders such as gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, and platinum, alloys thereof, and composite powders thereof. Examples of the metal particles include fine particles coated with a core and a material different from the core material, specifically, silver-coated copper powder in which the core is made of copper and the surface is coated with silver. The metal particles may be used alone or in combination of two or more types.

The metal particles preferably include metal nanoparticles. The metal nanoparticles are not particularly limited as long as they have an average particle size at the nano level, and are preferably 1 to 200 nm, more preferably 5 to 100 nm, even more preferably 8 to 80 nm, and particularly preferably 8 to 50 nm. The metal nanoparticles may be used alone with a specific average particle size, or may be used in combination with a plurality of nanoparticles with different average particle sizes.
By including metal nanoparticles, the activity of the particle surface increases, and the melting point decreases due to the nano-size effect, making it possible to sinter at a low temperature. In other words, low-temperature sintering makes it possible to lower the temperature when mounting electronic components, thereby reducing thermal stress. Furthermore, when the metal nanoparticles are bonded together by sintering and increase in size, they exhibit a high melting point equivalent to that of normal-sized metal materials (bulk metal materials), so the heat resistance temperature can be improved after mounting.

The content of metal nanoparticles is preferably 25 to 100% by mass, more preferably 80 to 100% by mass, even more preferably 90 to 100% by mass, and particularly preferably 95 to 100% by mass, based on 100% by mass of metal particles.

The average particle size of metal nanoparticles can be the cumulative particle size (D50) value of the volume particle size distribution measured using a Nanotrac UPA-EX150 (manufactured by Nikkiso Co., Ltd.). The average particle size of metal particles that are larger than metal nanoparticles can be the cumulative particle size (D50) value of the volume particle size distribution measured using a laser diffraction particle size distribution measuring device "SALD-3000" manufactured by Shimadzu Corporation.

<Fatty acids>
At least a portion of the surface of the metal particles is coated with a fatty acid including fatty acid A having 4 or more and 8 or less carbon atoms and fatty acid B having 14 or more and 20 or less carbon atoms.
The term "fatty acid" refers to a carboxylic acid (R-COOH) having one carboxyl group in the molecule, which has a chain structure, and includes those having a straight chain structure and those having a branched structure, and also includes saturated fatty acids and unsaturated fatty acids. As described below, fatty acids are not only used as raw materials for producing metal particles, but also exist near the metal surface even after the metal particles are generated by a reduction reaction, and function well as a dispersant that helps stabilize the fine particles.

[Fatty acid A having 4 to 8 carbon atoms and fatty acid B having 14 to 20 carbon atoms]
The fatty acid A having 4 to 8 carbon atoms mainly imparts the effect of low-temperature sinterability due to low-temperature decomposability. When the fatty acid A has 4 or more carbon atoms, the metal particles are stabilized and the aggregation of the particles is suppressed. Furthermore, when the fatty acid A has 8 or less carbon atoms, the decomposability at low temperatures is good and the low-temperature sinterability is excellent.
Examples of the fatty acid A having 4 to 8 carbon atoms include linear saturated fatty acids, linear unsaturated fatty acids, and branched fatty acids. Examples of linear saturated fatty acids include butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, and octanoic acid. Examples of linear unsaturated fatty acids include crotonic acid and isocrotonic acid. Examples of branched fatty acids include 2-ethylhexanoic acid.
As the fatty acid A having 4 to 8 carbon atoms, a straight-chain saturated fatty acid is preferred. A straight-chain fatty acid is preferred because it has excellent lipophilicity, improved stability in non-aqueous solvents, and a low decomposition temperature and excellent low-temperature sintering property. The fatty acid A having 4 to 8 carbon atoms may be used alone or in combination.

The fatty acid B having 14 to 20 carbon atoms mainly provides an effect of stabilizing metal particles. When the fatty acid B has 14 or more carbon atoms, the metal particles are stabilized, the aggregation of the particles is suppressed, and the viscosity of the bonding material is reduced, resulting in excellent coating suitability. Furthermore, when the fatty acid B has 14 or more carbon atoms, the affinity of the metal particles to non-aqueous solvents is improved. When the fatty acid B has 20 or less carbon atoms, the effect of low-temperature sintering is exhibited.
Examples of the fatty acid B having 14 or more and 20 or less carbon atoms include linear saturated fatty acids, linear unsaturated fatty acids, and branched fatty acids. Examples of linear saturated fatty acids include myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, and arachic acid. Examples of linear unsaturated fatty acids include palmitoleic acid, oleic acid, and erucic acid. Examples of branched fatty acids include 2-hexyldecanoic acid.
As the fatty acid B having 14 to 20 carbon atoms, a straight-chain unsaturated fatty acid is preferred. A straight-chain unsaturated fatty acid is preferred because it has excellent lipophilicity, improved stability in non-aqueous solvents, and a low decomposition temperature and excellent low-temperature sintering property. The fatty acid B having 14 to 20 carbon atoms may be used alone or in combination.
Therefore, by using fatty acid A and fatty acid B in combination, both the stability of the metal particles and the low-temperature sintering property can be achieved, which is preferable.

The boiling point of fatty acid A is preferably a temperature within ±0 to 20° C. of the boiling point of organic solvent C, and more preferably a temperature within ±0 to 10° C. of the boiling point of organic solvent C. When the boiling point difference is within the range of ±0 to 20° C., an excellent void reduction effect is exhibited.
For example, if the boiling point of fatty acid A is too high relative to the boiling point of organic solvent C, the organic solvent C volatilizes first, causing the film to become highly viscous, and the volatile components of fatty acid A that volatilize later cannot be discharged smoothly, causing the volatile components of fatty acid A to remain and form voids. On the other hand, if the boiling point of organic solvent C is too high relative to the boiling point of fatty acid A, the fatty acid A volatilizes first, and sintering progresses partially, causing the film to become highly viscous, and the volatile components of organic solvent C that volatilize later cannot be discharged smoothly, causing the volatile components of organic solvent C to remain and form voids.
By setting the boiling point of fatty acid A to a temperature within ±0 to 20°C of the boiling point of organic solvent C, both components volatilize at the same time, maintaining a low viscosity state and allowing the volatile components to be discharged smoothly. This reduces voids.

The boiling point of the fatty acid B is preferably a temperature within the boiling point of the organic solvent D ±0 to 50°C.
For example, if the boiling point of fatty acid B is too high relative to the boiling point of organic solvent D, organic solvent D volatilizes first, causing the inside of the film to become highly viscous, and the volatile components of fatty acid B that volatilize later cannot be discharged smoothly, causing the volatile components of fatty acid B to remain and form voids. On the other hand, if the boiling point of organic solvent D is too high relative to the boiling point of fatty acid B, fatty acid B volatilizes first, and sintering progresses partially, causing the inside of the film to become highly viscous, and the volatile components of organic solvent D that volatilize later cannot be discharged smoothly, causing the volatile components of organic solvent D to remain and form voids.
By setting the boiling point of fatty acid B to a temperature within ±0 to 50°C of the boiling point of organic solvent D, both components volatilize at the same time, maintaining a low viscosity state and allowing the volatile components to be discharged smoothly, thereby reducing voids.

The molar ratio of fatty acid A to fatty acid B (moles of fatty acid A/moles of fatty acid B) is preferably 0.5-30, more preferably 1-15, and even more preferably 2-8.
When the molar ratio of fatty acid A and fatty acid B is 0.5 or more, the ratio of fatty acid A, which has excellent low-temperature sinterability, becomes high, and the resulting bonding material has excellent low-temperature sinterability. As mentioned above, in the sintering process, fatty acid A volatilizes before fatty acid B due to the difference in carbon number, and the bonding material has a high viscosity at the stage when fatty acid B volatilizes, so the volatile components of fatty acid B tend to remain in the film of the bonding material more easily than fatty acid A, leading to void formation. Therefore, a high ratio of fatty acid A is preferable from the viewpoint of reducing voids in the film formed by the bonding material.
It is preferable that the molar ratio of fatty acid A to fatty acid B is 30 or less, since fatty acid B further stabilizes the metal particles.

The method for determining the molar ratio of fatty acid A and fatty acid B is not particularly limited, but examples include methods using pyrolysis GC or pyrolysis GC-MS. Specifically, a powder of metal particles coated with fatty acid is heated to above the boiling point of fatty acid B, and the volatile components generated are then introduced into a GC or GC-MS for analysis. From the area of the resulting chart, the molar ratio of fatty acid A and fatty acid B can be calculated by quantifying each component using a calibration curve.

<Production of Metal Particles Coated with Fatty Acids>
The method for producing the metal particles coated with fatty acid is not particularly limited, and they can be produced by a known method. Among them, the metal particles coated with fatty acid are preferably reduced metal compounds, more preferably reduced silver compounds using carbodihydrazide represented by the following formula (1) or polybasic acid polyhydrazide represented by the following formula (2).

［式（２）中、Ｒはｎ価の多塩基酸残基を表す。］

[In formula (2), R represents an n-valent polybasic acid residue.]

The carbodihydrazide or polybasic acid polyhydrazide functions as a reducing agent, and the reduction reaction may be carried out by either mixing a liquid medium with a metal salt compound of a fatty acid and then adding the carbodihydrazide or polybasic acid polyhydrazide to reduce the metal salt compound, or by mixing a liquid medium with a carbodihydrazide or polybasic acid polyhydrazide and then adding a metal salt compound of a fatty acid to reduce the metal salt compound.

The liquid medium in which the metal salt compound of the fatty acid is dispersed is not particularly limited, but considering the process of removing impurities, a non-aqueous solvent that undergoes phase separation from water is preferred, and after dispersing the metal salt compound of the fatty acid in the non-aqueous solvent, it is preferable to add an aqueous solution of carbodihydrazide or polybasic acid polyhydrazide, which is a reducing agent.

As the fatty acid of the metal salt compound of a fatty acid, it is preferable to use the above-mentioned fatty acid A having from 4 to 8 carbon atoms and/or fatty acid B having from 14 to 20 carbon atoms.
The metal capable of forming a metal salt compound of a fatty acid is not particularly limited, but is preferably at least one metal selected from Group VIII and Group IB metals such as gold, silver, copper, nickel, palladium, platinum, iron, cobalt, and mercury, and in consideration of low-temperature sintering, is preferably at least one metal selected from the group consisting of gold, silver, and copper.
The metal salt compound of fatty acid can be obtained by using a known method. For example, a commercially available fatty acid sodium salt or a fatty acid sodium salt obtained by mixing fatty acid and sodium hydroxide in water is dissolved in pure water, an equivalent amount of an inorganic salt of a target metal is added, and the precipitated metal salt compound of fatty acid is filtered by suction filtration and dried, whereby the metal salt compound of fatty acid can be easily obtained.
The inorganic salts of the above metals are not particularly limited, and examples thereof include chlorides such as chloroauric acid, chloroplatinic acid, and silver chloride, nitrates such as silver nitrate, acetates such as silver acetate and copper(II) acetate, perchlorates such as silver perchlorate, sulfates such as copper(II) sulfate, carbonates, silicates, phosphates, etc., and can be appropriately selected according to the desired metal. These inorganic salts of metals may be used alone or in combination of two or more.

The polybasic acid polyhydrazide represented by formula (2) is not particularly limited, and examples thereof include dibasic acid dihydrazide, tribasic acid trihydrazide, and tetrabasic acid tetrahydrazide. Among them, dibasic acid dihydrazide is preferred because it has good solubility in the solvent, which allows the reduction reaction to proceed uniformly, and it also has good storage stability.

Examples of dibasic acid dihydrazides include malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, dodecanoic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, tartaric acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, hexadecanoic acid dihydrazide, 2,6-naphthoic acid dihydrazide, 1,4-naphthoic acid dihydrazide, tartaric acid dihydrazide, malic acid dihydrazide, iminodiacetic acid dihydrazide, and itaconic acid dihydrazide.

Examples of tribasic acid trihydrazides include citric acid trihydrazide, trimellitic acid trihydrazide, nitriloacetic acid trihydrazide, and cyclohexanetricarboxylic acid trihydrazide. Examples of tetrabasic acid tetrahydrazides include ethylenediaminetetraacetic acid tetrahydrazide and pyromellitic acid tetrahydrazide.

Other examples of polybasic acid polyhydrazides include polyacrylic acid polyhydrazide, etc. These polybasic acid polyhydrazides may be used alone or in combination of two or more, and may also be used in combination with the carbodihydrazide of formula (1).
In the carbodihydrazide or polybasic acid polyhydrazide, one or more hydrogen atoms may be substituted with a functional group such as a hydroxyl group.

Considering purification after the reaction, it is preferable to add the reducing agent as an aqueous solution. Considering solubility in water, the reducing agent is preferably adipic acid dihydrazide, succinic acid dihydrazide, or glutaric acid dihydrazide.

In the process of dispersing a metal salt compound of a fatty acid in a liquid medium and carrying out a reduction reaction, a sufficient dispersion effect can be obtained for the metal salt compound of the fatty acid or the generated metal microparticles using only the fatty acid derived from the raw material, but if necessary, a compound having a dispersion stabilizing function (hereinafter sometimes referred to as a "dispersant") may be appropriately added.
The compound having the dispersion stabilizing function is not particularly limited, but is preferably a compound having one or more functional groups having affinity to metal compounds, such as an amino group, a quaternary ammonium salt, a hydroxyl group, a cyano group, a carboxyl group, a thiol group, or a sulfonic acid group. The functional group may be contained in the main chain of the compound, or in the side chain, or in both the main chain and the side chain. The compound having the functional group is not particularly limited, but is preferably used, for example, an amine compound, a pigment dispersant, a surfactant, a fatty acid, etc. The fatty acid may be the same fatty acid as the fatty acid of the metal salt compound of the fatty acid as the raw material, or may be a different fatty acid.

The particle size of the metal particles can be adjusted as needed, but is preferably 1 to 200 nm, more preferably 5 to 100 nm, even more preferably 8 to 80 nm, and particularly preferably 8 to 50 nm.

In 100% by mass of metal particles coated with fatty acids, the content of the fatty acids A and B is preferably 1 to 30% by mass, and more preferably 3 to 15% by mass. If the fatty acid content is 3% by mass or more, aggregation of the metal particles is further suppressed, resulting in excellent stability, which is preferable. If the fatty acid content is 15% by mass or less, voids are further reduced, which is preferable.

<Organic Solvent>
The bonding material of the present invention contains organic solvent C having a boiling point of 170° C. or more and 230° C. or less, and organic solvent D having a boiling point of 300° C. or more and 350° C. or less. Organic solvent C and organic solvent D having a boiling point within a predetermined range are not only dispersion media for dispersing metal particles, but also important components for smoothly releasing volatile components of fatty acid A and fatty acid B to the outside of the film during sintering and suppressing void formation.
Since the boiling point of the organic solvent C is 170°C or more and 230°C or less, the viscosity of the inside of the bonding material is reduced when the fatty acid A volatilizes and is discharged, and voids are reduced. In addition, the boiling point of the fatty acid A having 4 to 8 carbon atoms is close to the boiling point of the organic solvent C, so that both can volatilize efficiently. For the same reason, since the boiling point of the organic solvent D is 300 to 350°C, the viscosity of the inside of the bonding material is reduced when the fatty acid B volatilizes and is discharged, and voids are reduced. In addition, the boiling point of the fatty acid B having 14 to 20 carbon atoms is close to the boiling point of the organic solvent D, so that both can volatilize efficiently. Then, when the sintering is completed, the fatty acid A, fatty acid B, organic solvent C, and organic solvent D are all volatilized and discharged outside the film, forming a film with reduced voids.
Furthermore, since fatty acid B volatilizes after fatty acid A is discharged, it is possible to further reduce voids, so it is also important that the upper limit of the boiling point of organic solvent C (230°C) and the lower limit of organic solvent D (300°C) are not too close to each other.

Examples of organic solvents C having a boiling point of 170°C or higher and 230°C or lower include dipropylene glycol dimethyl ether (boiling point 175°C), ethylene glycol n-butyl ether acetate (boiling point 188°C), octanol (boiling point 195°C), Isopar L (boiling point 199°C), dihydroterpineol (boiling point 210°C), diethylene glycol monobutyl ether (boiling point 230°C), and 2-2-butoxyethoxyethanol (boiling point 230°C). These organic solvents C can be used alone or in combination as appropriate.

Examples of organic solvents D having a boiling point of 300°C or higher and 350°C or lower include polyethylene glycol monomethyl ether (boiling point 300°C), isobornylcyclohexanol (boiling point 318°C), benzyl benzoate (boiling point 324°C), and bis(2-ethylhexyl) adipate (boiling point 335°C). These organic solvents D can be used alone or in combination as appropriate.

The mass ratio of organic solvent C to organic solvent D (mass of organic solvent C/mass of organic solvent D) is preferably 1 to 3, and more preferably 1 to 2. A mass ratio of 1 or more promotes the discharge of the volatile components of fatty acid A outside the film and inhibits the volatile components of organic solvent D, which has a high boiling point, from remaining in the film, resulting in excellent void reduction. A mass ratio of 3 or less promotes the discharge of the volatile components of fatty acid B outside the film, resulting in excellent void reduction.

<Bonding material>
The bonding material of the present invention contains the above-mentioned metal particles coated with fatty acids, organic solvent C, and organic solvent D. The content of the metal particles coated with fatty acids relative to 100% by mass of the total solid content of the bonding material is preferably 80% by mass or more, more preferably 85 to 99% by mass, and even more preferably 90 to 99% by mass. By containing 80% by mass or more of the metal particles coated with fatty acids, it becomes possible to more firmly bond the members to be bonded together, which will be described later.

The bonding material of the present invention may contain a sintering accelerator. The sintering accelerator is a compound having a functional group with high affinity to metal particles, and due to the high affinity, it has the function of peeling off the organic matter covering the metal particles. The metal particles from which the organic matter has been peeled off lose their dispersion stability and aggregate, which promotes contact and fusion between the particles, forming a dense metal film.
There are no particular limitations on the functional group that has a high affinity for metal particles, and those containing nitrogen atoms in particular have a high affinity for metal particles and are preferably used as sintering accelerators.
The sintering accelerator containing a nitrogen atom is not particularly limited, and examples thereof include aromatic amines such as metaphenylenediamine and diaminodiphenylmethane, imidazole compounds such as 2-ethyl-4-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole and 1-cyanoethyl-2-methylimidazole, imidazoline compounds such as 2-methylimidazoline, dihydrazide compounds such as sebacic acid dihydrazide and isophthalic acid dihydrazide, amine adducts such as Amicure PN-23 and Amicure MY-24, and dicyandiamide. Among these, dicyandiamide is preferably used because of its high sintering-accelerating effect.
The sintering accelerator may be used alone or in combination of two or more.

The bonding material of the present invention may contain a dispersant from the viewpoint of preventing aggregation. Commercially available dispersants include, for example, Solsperse 9000, Solsperse 12000, Solsperse 17000, Solsperse 20000, Solsperse 21000, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000, Solsperse 32000, Solsperse 35100, Solsperse 54000, Solsix 250 (all manufactured by Lubrizol Japan Co., Ltd.), EFKA 4008, EFKA 4009, EFKA 4010, EFKA 4015, EFKA 4046, EFKA 4047, EFKA 4060, EFKA 4080, EFKA 7462, EFKA 4020, EFKA 4050, EFKA 4055, EFKA 4400, EFKA 4401, EFKA 4402, EFKA 4403, EFKA 4300, EFKA 4330, EFKA 4340, EFKA 6220, EFKA 6225, EFKA 6700, EFKA 6780, EFKA 6782, EFKA 8503 (all manufactured by Fuka Additives Co., Ltd.), Ajisper PA111, Ajisper PB711, Ajisper PB821, Ajisper PB822, Ajisper PN411, Famex L-12 (all manufactured by Ajinomoto Fine-Techno Co., Ltd.), DisperBYK101, DisperBYK102, DisperBYK106, DisperBYK108, DisperBYK109, DisperBYK200, DisperBYK201, DisperBYK202, DisperBYK203, DisperBYK204, DisperBYK205, DisperBYK206, DisperBYK208, DisperBYK209, DisperBYK301, DisperBYK302, DisperBYK306, DisperBYK308, DisperBYK309, DisperBYK401, DisperBYK402, DisperBYK403, DisperBYK501, DisperBYK502, DisperBYK506, DisperBYK502, DisperBYK503, DisperBYK601, DisperBYK602 ... rBYK111, DisperBYK116, DisperBYK130, DisperBYK140, DisperBYK142, DisperBYK145, DisperBYK1 61, DisperBYK162, DisperBYK163, DisperBYK164, DisperBYK166, DisperBYK167, DisperBYK168, Dis perBYK170, DisperBYK171, DisperBYK174, DisperBYK180, DisperBYK182, DisperBYK192, DisperBY K193, DisperBYK2000, DisperBYK2001, DisperBYK2020, DisperBYK2025, DisperBYK2050, DisperBYK 2070, Disper BYK2155, Disper BYK2164, BYK220S, BYK300, BYK306, BYK320, BYK322, BYK325, BYK330, BYK340, BYK350, BYK377, BYK378, BYK380N, BYK410, BYK425, BYK430 (all manufactured by BYK Japan K.K.).
The content of the dispersant is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, based on 100% by mass of the bonding material, in order to prevent residues during sintering. In order to prevent aggregation, the content is preferably 0.1% by mass or more.

<Joining method and article>
The article of the present invention comprises a first member and a second member joined together with a sintered body formed from the joining material of the present invention. Since the joining material is a conductive paste, the joined article can be developed into an electric circuit on an electronic substrate, such as an IC chip, and an electronic component mounted thereon.
The article of the present invention can be obtained by a manufacturing method including a step of applying a bonding material to at least a first member, and a step of contacting a second member with the bonding material on the first member and then firing the resulting product. The types of the first and second members are not particularly limited, and may be the same or different. The members may be appropriately processed by corona treatment, plating, or the like to increase the bonding strength.

Examples of the first and second members include metal members, electronic elements, plastic materials, and ceramic materials. Among these, it is preferable to join metal members together, a metal member and a semiconductor element, or a metal member and an LED element.
That is, it is preferable to sandwich the bonding material of the present invention between metal members, between a metal member and a semiconductor element, or between a metal member and an LED element, heat it to remove organic solvents and coating materials, and melt at least a portion of the metal particles to form a sintered body, and then bond the metal members together, between the metal member and the semiconductor element, or between the metal member and the LED element with the sintered body.

Examples of the metal member include a copper substrate, a gold substrate, and an aluminum substrate.
Examples of the electronic element include a semiconductor element and an LED element.
Semiconductor elements may be made of, for example, silicon, germanium, gallium arsenide, gallium phosphide, or cadmium sulfide.
Examples of LED elements include aluminum, silicon nitride, diamond, graphite, yttrium oxide, and magnesium oxide, and power device elements such as silicon carbide and gallium nitride can also be used.
Examples of plastic materials include polyimide, polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, and polyethylene naphthalate.
Examples of ceramic materials include glass and silicon.

The method for applying the bonding material is not particularly limited as long as it can be applied uniformly to the member, and examples include various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, and gravure offset printing, or the dispenser method.

The firing conditions in the bonding step can be appropriately adjusted, but examples of the firing conditions include atmospheric pressure, a nitrogen atmosphere, a vacuum, a pressurized or reducing atmosphere, and a temperature of 200 to 300°C.
Examples of the baking device include a hot air oven, an infrared oven, a reflow oven, a microwave oven, and a light baking device. In the case of a light baking device, the type of light to be irradiated is not particularly limited, and examples thereof include a mercury lamp, a metal halide lamp, a chemical lamp, a xenon lamp, a carbon arc lamp, and a laser light. These devices can be used alone or in combination as appropriate.

The present invention will be described in more detail below using examples and comparative examples, but the technical scope of the present invention is not limited thereto. Parts and % represent parts by mass and % by mass.

<Production of Metal Particles>
(Silver particles 1)
A separable 4-neck flask was fitted with a cooling tube, a thermometer, a nitrogen gas inlet tube, and a stirrer, and 200 parts of toluene and 22.3 parts of silver hexanoate were charged under a nitrogen atmosphere and stirred at room temperature to obtain a 0.5M solution, and then 2.3 parts of diethylaminoethanol (0.2 mol times per mol of metal) and 2.8 parts of oleic acid (0.1 mol times per mol of metal) were added as dispersants and dissolved. Then, 73.1 parts of a 20% solids concentration aqueous solution of succinic acid dihydrazide (hereinafter, SUDH) (2 mol times hydrazide group per mol of metal) were dropped as a reducing agent, and the liquid color changed from pale yellow to dark brown. In order to further promote the reaction, the temperature was raised to 40 ° C., and the reaction was allowed to proceed. After standing and separating, the aqueous phase was removed to remove excess reducing agent and impurities, and distilled water was added to the toluene layer several times, followed by repeated washing and separation to obtain a toluene dispersion of nanoparticles. 2.4 parts of hexanoic acid was added to this toluene dispersion, and a poor solvent was further added, followed by repeating centrifugation and washing, and then drying, to obtain Silver Powder 1. The average particle size of Silver Powder 1 was 10 nm.

(Silver particles 2)
Silver powder 2 was obtained in the same manner as silver powder 1, except that 22.3 parts of silver hexanoate was replaced with 19.5 parts of silver butanoate, and 2.4 parts of hexanoic acid was added to the toluene dispersion with 1.9 parts of butanoic acid. The average particle size of silver powder 2 was 10 nm.

(Silver particles 3)
Silver Powder 3 was obtained in the same manner as Silver Powder 1, except that 22.3 parts of silver hexanoate was replaced with 25.1 parts of silver octanoate, and 2.4 parts of hexanoic acid was added to the toluene dispersion with 3.0 parts of octanoic acid. The average particle size of Silver Powder 3 was 10 nm.

(Silver particles 4)
Silver Powder 4 was obtained in the same manner as Silver Powder 1, except that 2.8 parts of oleic acid was changed to 2.3 parts of myristic acid. The average particle size of Silver Powder 4 was 10 nm.

(Silver particles 5)
Silver Powder 5 was obtained in the same manner as Silver Powder 1, except that the amount of hexanoic acid added to the toluene dispersion was changed from 2.4 parts to 9.8 parts. The average particle size of Silver Powder 5 was 10 nm.

(Silver Particles 6)
Silver Powder 6 was obtained in the same manner as in Example 1, except that 2.4 parts of hexanoic acid was added to the toluene dispersion, and 5.9 parts of oleic acid was added. The average particle size of Silver Powder 6 was 10 nm.

(Silver particles 7)
A separable 4-neck flask was fitted with a cooling tube, a thermometer, a nitrogen gas inlet tube, and a stirrer, and 200 parts of toluene and 22.3 parts of silver hexanoate were charged while stirring at room temperature under a nitrogen atmosphere to obtain a 0.5M solution, and then 2.3 parts of diethylaminoethanol (0.2 mol times per mol of metal) and 2.8 parts of oleic acid (0.1 mol times per mol of metal) were added as dispersants and dissolved. Then, 10.0 parts of hydrazine monohydrate (2 mol times per mol of metal) was added, and the reaction proceeded vigorously. Next, 100 parts of distilled water was added, left to stand and separated, and the aqueous layer was removed to remove precipitates, excess reducing agent, and impurities. Distilled water was further added to the toluene layer several times, and washing and separation were repeated to obtain a toluene dispersion of nanoparticles. 2.4 parts of hexanoic acid were added to this toluene dispersion, and a poor solvent was further added, followed by repeated centrifugation and washing, and drying to obtain silver powder 7. The average particle size of silver powder 7 was 20 nm.

(Silver Particles A)
A separable 4-neck flask was fitted with a cooling tube, a thermometer, a nitrogen gas inlet tube and a stirrer, and 200 parts of toluene and 22.3 parts of silver hexanoate were charged under a nitrogen atmosphere at room temperature while stirring to obtain a 0.5M solution. Then, 2.3 parts of diethylaminoethanol (0.2 mol times per mol of metal) and 1.2 parts of hexanoic acid (0.1 mol times per mol of metal) were added as dispersants and dissolved. Then, 73.1 parts of a succinic acid dihydrazide aqueous solution with a solid content concentration of 20% (2 mol times the hydrazide group per mol of metal) were dropped as a reducing agent, and the liquid color changed from pale yellow to dark brown. In order to further promote the reaction, the temperature was raised to 40 ° C., and the reaction was allowed to proceed. After standing and separating, the aqueous phase was removed to remove excess reducing agent and impurities, and distilled water was added to the toluene layer several times, followed by repeated washing and separation to obtain a toluene dispersion of nanoparticles. After adding a poor solvent to this toluene dispersion, centrifugation and washing were repeated, and drying was performed to obtain silver powder A. The average particle size of the silver powder A was 20 nm.

(Silver Particles B)
Silver powder B was obtained in the same manner as silver powder A, except that 22.3 parts of silver hexanoate was replaced with 38.9 parts of silver oleate, and 1.2 parts of hexanoic acid was added to the toluene dispersion with 2.8 parts of oleic acid. The average particle size of silver powder B was 800 nm.

(Silver Particles C)
Silver Powder C was obtained in the same manner as Silver Powder 1, except that 22.3 parts of silver hexanoate was replaced with 16.7 parts of silver acetate, and 2.4 parts of hexanoic acid was added to the toluene dispersion with 1.3 parts of acetic acid. The average particle size of Silver Powder C was 10 nm.

(Silver Particles D)
Silver Powder D was obtained in the same manner as Silver Powder 1, except that 22.3 parts of silver hexanoate was replaced with 27.9 parts of silver decanoate, and 2.4 parts of hexanoic acid was added to the toluene dispersion with 3.6 parts of decanoic acid. The average particle size of Silver Powder D was 10 nm.

(Silver Particles E)
Silver Powder E was obtained in the same manner as Silver Powder 1, except that 2.8 parts of oleic acid was changed to 2.0 parts of lauric acid. The average particle size of Silver Powder E was 10 nm.

(Silver Particles F)
Silver Powder F was obtained in the same manner as Silver Powder 1, except that 2.8 parts of oleic acid was changed to 3.4 parts of erucic acid. The average particle size of Silver Powder F was 10 nm.

The molar ratios of fatty acids A and B coating silver particles 1 to 7 and silver particles A to F were calculated by quantitatively analyzing the volatile components generated by heating the silver particles to 400°C or higher using a GC-MS (QP-5050, manufactured by Shimadzu Corporation) equipped with a pyrolysis injection device. The results are shown in Table 1.

<Adjustment of bonding material>
[Example 1] (Preparation of bonding material 1)
90.0 parts of silver particles 1, 6.0 parts of Isopar L (manufactured by Exxon Mobil Corp., boiling point 199° C.), and 4.0 parts of Tersolve MTPH (manufactured by Nihon Terpene Chemical Co., Ltd., isobornylcyclohexanol, boiling point 318° C.) were mixed to obtain a bonding material 1.

[Examples 2 to 14, Comparative Examples 1 to 10] (Preparation of Bonding Materials 2 to 24)
Bonding materials 2 to 24 were obtained in the same manner as bonding material 1, except that the types and amounts of metal particles, organic solvent, and sintering accelerator were changed to those shown in Table 1.

<Evaluation of bonding materials>
The obtained bonding material was subjected to the following evaluations. The results are shown in Table 1.

[viscosity]
The viscosity was measured using an E-type viscometer one minute after the start of rotation after leaving the bonding material at 25° C. for one day, and the measured value was (Pa·s).

[Coating suitability]
The bonding material was applied to a steel plate under the following conditions, and its coatability was evaluated according to the following criteria.
(Coating conditions)
Metal mask: opening 4 mm square, plate thickness 50 μm (manufactured by Celia Corporation)
Metal squeegee: 40 mm x 250 mm, thickness 1 mm (manufactured by Seria Corporation)
(Evaluation Criteria)
A: The adhesive is evenly attached to the entire opening (4 mm square area). B: The adhesive is attached to only a portion of the opening (3-3.7 mm square area). C: The adhesive is attached to only a portion of the opening (2-3 mm square area). D: The adhesive is attached to less than a 2 mm square area of the opening.

[Bonding strength (shear strength)]
The bonding material was applied to the substrate 1 under the following coating conditions, and the substrate 2 was attached. The temperature was then raised from 25°C to 300°C at 5°C per minute, and sintered at 300°C for 120 minutes in an air atmosphere to obtain an article, which was used as a test piece. The thickness of the bonding material when applied was 50 μm, which was the same as the plate thickness of the metal mask used.
(Coating conditions)
Metal mask: opening 4 mm square, plate thickness 50 μm (manufactured by Celia Corporation)
Metal squeegee: 40 mm x 250 mm, thickness 1 mm (manufactured by Seria Corporation)
Substrate 1: Copper plate 1.3 cm x 1.3 cm (thickness 2 mm)
Substrate 2: Si chip 5 mm x 5 mm (thickness 300 μm)

The bond strength of the obtained test pieces was measured before and after the following thermal cycle test. The bond strength was measured by using a universal bond tester (manufactured by DAGE JAPAN, 4000 series) to fix the substrate 1 and push the interface between the substrate 1 and the sintered body toward the substrate 2 at a height of 100 μm at a speed of 500 μm/s, and the strength [MPa] at which the bond was broken was measured.
(Cooling and heating cycle test)
The test piece was held at -40°C for 30 minutes and then held at 150°C for 30 minutes, which constituted one cycle of treatment. This treatment was repeated 500 times.

The abbreviations in Table 1 are as follows.
Isopar L: Exxon Mobil Corporation, boiling point 199°C
MTPH: isobornylcyclohexanol, boiling point 318°C, manufactured by Nihon Terpene Chemical Co., Ltd.
DICY7: Mitsubishi Chemical Corporation, JER Cure DICY7, sintering accelerator

From Table 1, the bonding material of the present invention, which is a combination of two fatty acids having specific carbon numbers and two organic solvents having specific boiling points, has sinterability at a relatively low temperature of about 300° C. and is excellent in bonding strength before and after thermal cycles.
In particular, Example 1, in which the boiling point difference between fatty acid A and solvent C and the boiling point difference between fatty acid B and solvent D were small, showed superior bonding strength before and after thermal cycles compared with Examples 3, 4 and 8.
Comparing Example 1 with Examples 6 and 7, Example 1, in which the mass ratio of organic solvent C to organic solvent D (mass of organic solvent C/mass of organic solvent D) was within the range of 1 to 3, showed superior bonding strength before and after the thermal cycle.
Comparing Example 1 with Examples 13 and 14, Example 1, in which the molar ratio of fatty acid A and fatty acid B (moles of fatty acid A/moles of fatty acid B) was within the range of 2 to 5, showed superior bonding strength before and after thermal cycles.
Comparing Example 1 with Example 5, Example 1 showed superior bonding strength before and after the thermal cycle. This is presumably because silver particles 1 contained in Example 1 had a smaller average particle size and a more uniform particle size distribution, which improved coatability due to the lower viscosity and reduced voids due to the dense arrangement of particle sizes.

On the other hand, the bonding strength before and after the thermal cycle was insufficient in Comparative Examples 1 and 2, which did not contain a high boiling point solvent. This is presumably because the amount of voids increased due to the absence of a high boiling point solvent.
Comparative Example 3, which contains two kinds of metal particles coated with a single coating material, had insufficient bonding strength before and after the thermal cycle. This is presumably because one metal particle is coated with a kind of fatty acid, so the silver particles coated with a coating material with a lower boiling point start sintering first, and after the coating film hardens, the silver particles coated with the other coating material with a higher boiling point sinter, which prevents gas from being discharged smoothly and causes many voids to form inside the film.
Comparative Examples 4 to 10, which used inappropriate combinations of coating materials and organic solvents, showed insufficient bonding strength before and after thermal cycling. This is presumably because gas was not discharged smoothly and many voids were formed inside the film.

Claims (7)

A bonding material comprising metal particles coated with a fatty acid and an organic solvent,
The metal particles are each coated with a fatty acid, the fatty acid including fatty acid A having 4 to 8 carbon atoms and fatty acid B having 14 to 20 carbon atoms, at least a part of the particle surface of the metal particle being coated with the fatty acid,
the metal particles are silver nanoparticles,
The bonding material, wherein the organic solvent includes organic solvent C having a boiling point of 170° C. or more and 230° C. or less, and organic solvent D having a boiling point of 300° C. or more and 350° C. or less. The bonding material according to claim 1, in which the molar ratio of fatty acid A to fatty acid B (moles of fatty acid A/moles of fatty acid B) is 0.5 to 30. The bonding material according to claim 1 or 2, in which the mass ratio of organic solvent C to organic solvent D (mass of organic solvent C/mass of organic solvent D) is 1 to 3. The bonding material according to any one of claims 1 to 3, wherein the boiling point of fatty acid A is a temperature within ±0 to 20°C of the boiling point of organic solvent C. The bonding material according to any one of claims 1 to 4, wherein the boiling point of fatty acid B is a temperature within ±0 to 50°C of the boiling point of organic solvent D. The metal particles are a reduction product obtained by reducing a silver compound using a carbodihydrazide represented by the following formula (1) or a polybasic acid polyhydrazide represented by the following formula (2). The bonding material according to any one of claims 1 to 5.

[In formula (2), R represents an n-valent polybasic acid residue.] An article in which metal members are bonded together, a metal member and a semiconductor element, or a metal member and an LED element are bonded together with a sintered body formed from the bonding material according to any one of claims 1 to 6.