JP5824201B2 - Bonding material and bonding method using the same - Google Patents

Description

  The present invention relates to a bonding material and a bonding method using the same, and particularly to a metal nanoparticle used for metal-to-metal bonding.

  Metals are known to exhibit size-specific physical properties when the particle size is reduced. In particular, when the particles become nano-order, the tendency becomes remarkable. An attempt has been made to use, for example, metal nanoparticles as a bonding material between different substances using such properties (see, for example, Patent Document 1).

  In the case where only metal nanoparticles are used alone, as is well known, it is necessary to form a film mainly composed of an organic substance on the surface. However, it is not easy to remove the organic substance covering the surface of the metal nanoparticles that is not required in the bonding, and it is necessary to remove by heating for a long time or at a high temperature. This was one of the causes that hindered the practicality of bonding using metal nanoparticles.

  Therefore, in Patent Document 2, a metal nanoparticle aggregate obtained by agglomerating nanoparticles and a metal nanoparticle coexist to produce a composition having two or more particle diameter peaks, and this is used as a bonding material. Is disclosed. In this method, a bonded body having high shear strength is obtained.

  Patent Document 3 discloses a technique related to joining by mixing and pressurizing and heating composite metal particles composed of an organic substance and a metal, the organic substance, and silver carbonate or silver oxide. Patent Document 4 or Non-Patent Documents 1 and 2 disclose a technique in which an oxide layer containing oxygen is formed at a bonding interface, and a bonded body is formed using a bonding material composed of metal compound particles and an organic material. .

Japanese Patent No. 2794360 JP 2008-161907 A JP 2009-279649 A JP 2008-208442 A

Morita et al. "Joint technology using silver oxide microparticles" Journal of Japan Institute of Electronics Packaging p. 110 Vol. 12 No. 2 (2009) Morita et al. “Development of lead-free bonding technology for high-temperature environments using micrometer-sized silver oxide particles” MATERIA Vol. 49 No. 1 (2010)

  Patent Document 1 uses nanoparticles alone for bonding, and as described above, has not yet provided a sufficient strength for bonding. Moreover, the technique of patent document 2 aggregates a nanoparticle, provides a particle | grain with a comparatively large particle diameter, and forms a conjugate | zygote by using these together. However, as a result, a process of aggregating the nanoparticles is required, which is not necessarily advantageous from an industrial viewpoint. In addition, although agglomerated, the substance involved in bonding is the nanoparticles themselves, and the bonding strength depends on the characteristics of the nanoparticles.

  Moreover, in the technique described in Patent Document 2, unevenness may occur in the bonded state depending on the presence state of the aggregate-nanoparticles. Therefore, it is necessary to pay close attention to the presence state of the aggregate-dispersion, in other words, the dispersibility of the particles. In addition, if an attempt is made to strengthen dispersion in order to obtain high dispersibility, aggregates are destroyed. As a result, there is a possibility that the effect of improving the bonding strength achieved by the coexistence of the agglomerates and nanoparticles may be drastically reduced.

  Further, the contents described in Patent Documents 3 and 4 and Non-Patent Documents 1 and 2 form a joined body by adding different components such as iron carbonate and organometallic salt in addition to metal nanoparticles. Therefore, it requires a decomposition reaction of carbonate or oxide, and is not necessarily efficient.

  That said, the method itself of interposing metal nanoparticles in the gaps between relatively large metal particles can easily cause bonding between large metal particles, and has a significant effect on improving the bonding strength. You can expect to give.

  Therefore, the problem to be solved by the present invention is to provide a bonding metal paste (bonding material) that can secure bonding strength and reduce unevenness in bonding strength even with the simplest possible structure. Decided.

  The inventors diligently studied these problems, and found that the above problems could be solved by the structure of the bonding material described below, and completed the present invention.

Bonding material to solve the above problems, is measured by Microtrac particle size distribution analyzer, and the metallic sub-micron particles mean a primary particle diameter (D ₅₀ diameter) 0.5 to 3.0 [mu] m, an average primary particle size of 1 ˜200 nm, and composed of metal nanoparticles coated with a fatty acid having 6 carbon atoms and a dispersion medium for dispersing them.

  The weight ratio of the metal nanoparticles to the metal submicron particles (metal nanoparticle / metal submicron particle) is 0.1 to 10.0.

Preferably, the organic compound covering the surface of the metal nanoparticles is selected from fatty acids having at least one unsaturated bond.

  Furthermore, the dispersing agent is a bonding material containing 0.5% to 2.5% of the total amount of metal components of the metal nanoparticles and the metal submicron particles.

  Moreover, it is preferable that the metal seed | species which comprises the said metal submicron particle and the said metal nanoparticle is silver.

  As a bonding method using the above-mentioned bonding material, a step of applying the bonding material described above to the bonding surface, and heating at a temperature equal to or lower than the sintering temperature of the metal nanoparticles while pressing the object to be bonded to the bonding surface It is preferable to have a 1st heating process and a 2nd heating process which heats heating temperature to 200 to 400 degreeC. At this time, the bonding material may be applied to either the object to be bonded or the bonded object, or may be applied to both. Note that the press contact is not necessarily required and may be omitted depending on circumstances.

  In the above bonding method, the heating time in the first and second heating steps may be as short as 30 seconds or more and 60 minutes or less.

  By employing the bonding material and the bonding method of the present invention, it is possible to obtain a bonded body having high bonding strength as a problem and reduced variation in bonding strength.

It is the schematic diagram which showed the process of the joining method concerning this invention. It is a figure showing the relationship between a viscosity and bonding strength.

  The metal nanoparticles used in the present invention have an average primary particle diameter calculated from a transmission electron micrograph of 1 to 200 nm, preferably 1 to 150 nm, more preferably 1 to 100 nm. By employing metal nanoparticles having such a particle size, it is possible to provide a bonding paste that can easily cope with the bonding object and bonding conditions.

  Since metal nanoparticles have very high activity on the particle surface, if the metal surface is exposed, adjacent particles may sinter or oxidize in air. In general, it is known that if the surface of a metal nanoparticle is coated with an organic compound, oxidation and sintering are suppressed, and the particle can be stored in a stable state independently. However, when the molecular weight of the organic compound to be coated becomes too large, it becomes difficult to decompose or evaporate even when heated somewhat when used as a bonding material. Since the bonding material forms a bonding layer at the bonding interface, if an organic compound or carbon burnt in the bonding layer remains in the bonding layer, it causes a decrease in bonding strength. Therefore, in order to easily remove carbon, it is preferable to use one having a small number of carbon atoms.

  On the other hand, when the molecular weight of the organic compound to be coated is too small, the particles are less likely to exist stably, and handling becomes difficult. If this viewpoint is followed, the organic compound which coat | covers the surface of these metal nanoparticles needs to have a moderate molecular weight. That is, the organic compound that coats the surface of the metal nanoparticles has a molecular weight that is easy to handle, and needs to be a moderately short molecular chain in order to obtain low-temperature sinterability.

  The present inventor has found that the organic compound constituting the surface of the metal nanoparticles is a carboxylic acid in order to satisfy both of these requirements. Moreover, the bond form of the carboxylic acid at this time may be saturated or unsaturated. In addition, when the organic compound has an unsaturated bond in the structure, the organic compound may have a double or triple bond, or may have an aromatic ring in the structure. good. In particular, it was found that the bonding strength was increased by using metal nanoparticles coated with unsaturated fatty acids. In particular, among fatty acids, carboxylic acids having about 6 to 8 carbon atoms are preferred.

  In the present invention, not only metal nanoparticles coated with one kind of organic compound, but also metal nanoparticles coated with different organic compounds may be mixed and used. For example, a mixture of metal nanoparticles whose surface is coated with saturated fatty acid and metal nanoparticles whose surface is coated with unsaturated fatty acid may be used. The bonding material of the present invention is also preferably configured to disperse metal nanoparticles in a polar solvent and impart fluidity. The advantage of using a polar solvent is that it has a lower vapor pressure and is suitable for handling at the same temperature compared to nonpolar solvents.

On the other hand, it is preferable to use silver particles having an average particle size of 0.5 μm or more as metal particles of submicron order (hereinafter referred to as “metal submicron particles”). Calculation of the average particle diameter in this specification was performed based on the laser diffraction method according to the following procedure. First, 0.3 g of a silver particle sample was placed in 50 mL of isopropyl alcohol, dispersed for 5 minutes with an ultrasonic cleaner with an output of 50 W, and then laser diffracted by a microtrack particle size distribution measuring device (Honeywell-Nikkiso 9320-X100). The value of D ₅₀ (cumulative 50% by mass particle size) measured by the method was defined as the average primary particle size of the metal submicron particles.

  At this time, the average primary particle size of the metal submicron particles is 0.5 to 3.0 μm, preferably 0.5 to 2.5 μm, more preferably 0.5 to 2.0 μm. Thus, it becomes possible to provide a bonded body having a high bonding force. On the other hand, when metal submicron particles having such a particle size distribution are used, the above-described metal nanoparticles having an average primary particle diameter of 1 to 200 nm are likely to be mixed in the gaps between the metal submicron particles. As a result, the metal nanoparticles can be sintered and the bonding strength can be increased. The surface of the particles may be coated with an organic substance for improving dispersibility. However, the effect of the present invention is not reduced even if the particle is not coated, so the type of the organic substance is not limited. However, it is not preferable that the polymer is formed by polymerization because it is difficult to decompose.

  In the present invention, the dispersion medium is mainly a polar solvent, in which metal nanoparticles and metal submicron particles are dispersed. As such a polar solvent, water or an organic solvent having a polar group can be used.

  The mixing ratio (metal nanoparticle / metal submicron particle) based on the mass ratio of the metal component of the metal nanoparticle coated with the organic compound and the metal submicron particle is preferably 0.1 to 10.0, preferably It is 0.15-9.0, More preferably, it is 0.2-5.0. By setting the mass ratio of the metal component of the metal nanoparticles coated with the organic compound and the metal submicron particles to this ratio, the metal nanoparticles are more present in the voids, which is preferable because sintering is promoted. .

  When dispersing metal nanoparticles and metal submicron particles in a polar solvent, a dispersant may be further added. Since metal nanoparticles have a property of easily agglomerating, in some cases, by adding a known dispersing agent, it is possible to make the submicron particles and the nanoparticles easily blended and to facilitate the joining. In addition, since the dispersing agent used at this time eliminates an adverse effect on the bonding strength, a material that is easily decomposed by heat or has a small amount of ignition residue can be suitably used.

  In addition, since the bonding material of the present invention is mainly provided in a paste form, application to the bonding site is easier when it has an appropriate viscosity. Further, according to the study by the present inventors, it is possible to form a stronger bonded body by adjusting the viscosity. From these examination results, the bonding material of the present invention is finally provided at a viscosity of 10 to 250 Pa · s (25 ° C., 5 rpm, C (cone): value at 35/2) at room temperature. The pressure is preferably 100 Pa · s or less, more preferably 50 Pa · s or less.

  Hereinafter, the bonding material completed by the present invention will be described in detail.

<Synthesis of particles>
As the bonding material used in the present invention, metal nanoparticles to which a saturated or unsaturated fatty acid having 6 to 8 carbon atoms, particularly carboxylic acid or a derivative thereof is attached or bonded are used. By making the surface of the metal nanoparticles coated with an organic compound, the metal nanoparticles can stably exist without agglomeration during drying or dispersion in a polar solvent.

  A saturated or unsaturated organic compound having 6 to 8 carbon atoms functions as a protective agent for the metal nanoparticles. This protective agent is attached to the surface of the metal nanoparticles, and has an effect of inhibiting fusion between the particles and obtaining stable metal nanoparticles. For the metal nanoparticles of the present invention, relatively short linear fatty acids are preferred. Specifically, the length is particularly preferably about as long as hexanoic acid, heptanoic acid, octanoic acid, sorbic acid, benzoic acid, salicylic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, and adipic acid. Moreover, if it is the particle | grains coat | covered with such an organic compound, for example, the particle | grains coat | covered with hexanoic acid or sorbic acid, a metal nanoparticle can also be obtained as a powder state. Therefore, storage stability and handling are easy even when added to other nanoparticles.

  Next, the manufacturing method of the metal nanoparticle used for this invention is demonstrated. In the method for producing metal nanoparticles, a liquid preparation step for adjusting the raw material liquid and the reducing liquid, a temperature raising step for increasing the temperature, a reaction step for adding the raw material liquid to the reducing liquid and advancing the reaction to obtain metal nanoparticles, A ripening process for growing metal particles (especially silver particles) in the liquid, a washing process for removing excess organic compounds by repeating filtration, washing with water, and dispersion, and a drying process for removing water in the liquid by drying are performed. .

  In the present invention, the reducing liquid preparation step, the reaction step, and the washing step are performed as follows. The reducing solution used in the preparation step of the reducing solution includes water, aqueous ammonia, hexanoic acid (or sorbic acid or the like) that is an organic compound, and a hydrazine hydrated aqueous solution. In the reaction step of the metal nanoparticles, a metal salt, particularly an aqueous nitrate solution is added to the reducing solution and reacted with the reducing solution. In the washing step, the product obtained in the reaction step is washed with water.

  By such a process, the metal nanoparticles are stably present even in a polar solvent, and metal nanoparticles having an average primary particle diameter of 200 nm or less can be obtained. The ammonia water included in the reducing solution is added to dissolve the acid in the water.

  In the reaction step of the metal nanoparticles of the present invention, the reaction solution in the reaction tank is preferably heated to a temperature in the range of 40 ° C. to 80 ° C. for reaction. In addition, if it is less than 40 degreeC, since the supersaturation degree of a metal will rise and a nucleus generation will be accelerated | stimulated, since a particle size distribution tends to become uneven, it is not preferable. Further, when the temperature exceeds 80 ° C., nucleation is suppressed, but it becomes difficult to control the particle growth, so that large particles and small particles are randomly present, which is also not preferable.

  Moreover, in the reaction step of the metal nanoparticles of the present invention, it is preferable to add a metal salt aqueous solution such as nitrate to be added all at once from the viewpoint of realizing a uniform reaction in the solution. If not added all at once, the solution becomes heterogeneous, and nucleation and particle aggregation occur simultaneously. As a result, metal nanoparticles having a large particle size distribution and a non-uniform shape are generated. Therefore, “added all at once” as used herein means that the reaction factor such as the concentration, pH, or temperature of the reducing agent or protective agent (organic compound, etc.) does not substantially change depending on the addition time of the aqueous metal salt solution such as nitrate. Refers to an embodiment. In other words, the method of “adding all at once” is not particularly limited as long as a uniform reaction in the solution can be realized. Further, in the formation stage of the metal nanoparticles, Cu may be present together for the purpose of adjusting the particle form.

Here, the hydrazine hydrate in the present invention is not particularly limited as long as it can reduce a metal as a reducing agent. Reducing agents other than hydrazine hydrate, specifically hydrazine, borohydride alkali salts (NaBH ₄ etc.), lithium aluminum hydride (LiAlH ₄ ), ascorbic acid, primary amine, secondary amine, tertiary A secondary amine can also be used in combination.

  Next, after performing the reaction step and the washing step of the present invention, a step of dispersing the fine particles in a polar solvent is performed. Here, the dispersion means a state in which fine particles are stably present in a polar solvent, and as a result of standing, a part of the fine particles may be precipitated. Further, a dispersing agent may be added to the dispersion so that the metal nanoparticles are easily dispersed.

  By performing such a process, a composition in which metal nanoparticles having an average primary particle size of 200 nm or less are dispersed in a polar solvent together with a dispersant is obtained.

  In the manufacturing method of the metal nanoparticles of the present invention described above and the manufacturing method of the composition including the same, it is preferable to use a reaction vessel having a shape and a structure capable of obtaining uniform stirring. This is because the metal nanoparticles according to the present invention have a very small particle size, so that the local concentration and pH distribution greatly affect the particle size distribution.

  Then, about one Embodiment of the manufacturing method of the metal nanoparticle of this invention, each manufacturing process is demonstrated along the flow of reaction.

<Preparation process>
In this step, two types of liquids are prepared. One is a liquid I in which a reducing substance (reducing agent) is dissolved (hereinafter referred to as a reducing liquid), and the other is a liquid II in which a metal salt as a raw material is dissolved (hereinafter referred to as a raw material liquid). It is. The reducing solution is obtained by dissolving the above-described reducing agent in pure water, adding an organic compound serving as a protective agent and ammonia water as a stabilizer, and mixing until uniform. The raw material liquid is obtained by dissolving metal salt crystals in pure water. The order of addition may be changed so that the protective agent is easily dissolved. Moreover, you may heat at temperature lower than a reaction process so that melt | dissolution may advance easily.

<Temperature raising process>
After preparing each liquid, each liquid is heated using a water bath or a heater, and it raises to reaction temperature. At this time, if the reducing liquid and the raw material liquid are heated in the same manner and the temperature difference between the two liquids is eliminated, it is possible to prevent a problem that mixing cannot be performed at once due to convection caused by the temperature difference. Further, there is an effect of preventing non-uniform reaction caused by a difference in temperature, and it is preferable because the uniformity of particles can be maintained. At this time, the target temperature (later reaction temperature) to be raised is in the range of 40 to 80 ° C.

<Reaction process>
When each liquid rises to the target temperature, the raw material liquid is added to the reducing liquid. It is preferable to carry out the addition at once in consideration of bumping, from the viewpoint of the uniformity of the reaction.

<Aging process>
After mixing the reaction solution, stirring is continued for about 10 to 30 minutes to complete the growth of particles. The end point of the reaction at this time is judged by confirming whether or not the reaction of unreduced silver occurs by dropping hydrazine into the sampled reaction solution.

<Washing process>
The obtained slurry is washed by repeating a known solid-liquid separation method. As the solid-liquid separation method, specifically, a method using a filter press, a method of performing solid-liquid separation by forcibly sedimenting particles using a centrifugal separator, or the like can be used.

  For example, when centrifugation is used, the following procedure is used. First, it is centrifuged at 3000 rpm for 30 minutes. Next, after the solid-liquid separation, the supernatant is discarded, pure water is added, and the mixture is dispersed with an ultrasonic disperser for 10 minutes. By repeating the steps of centrifugation, supernatant disposal, addition of pure water, and ultrasonic dispersion several times, excess organic compounds adhering to the particles are removed to form a washing step. At this time, the conductivity of the supernatant or discharged water can be measured to confirm the quality of cleaning.

  In addition, when using solid-liquid separation with a filter press, after separating the reaction solution, washing with water in the forward direction and washing with water in the reverse direction to remove organic compounds adhering to the particle surface can do. At this time, similarly to the above, the conductivity of the supernatant or discharged water can be confirmed to confirm the quality of the cleaning.

<Drying process>
The solid (cake form) obtained in this way is powdered through a drying process. In this way, the nanoparticles can be stored in a stable form for a long time. For the drying at this time, a method using freeze drying or vacuum drying or a known drying method can be employed. However, if the drying temperature is too high, the organic compound that coats the metal surface may scatter and the nanoparticles may not be able to maintain the primary particles. Therefore, it is preferable that the drying process is carried out for a long time at a temperature not higher than the decomposition temperature of the organic compound covering the particle surface. As an example of specific drying conditions, the drying time is 12 hours or more in the atmosphere at a temperature of 60 ° C.

  Commercially available metal particles can be used as the submicron order metal particles. For example, the submicron-order metal particles produced using the method described in Japanese Patent No. 4025839 concerning the present applicant can be used.

<Paste>
The metal submicron particles and the metal nanoparticle mass obtained by using the method as described above are added to a polar solvent (dispersion medium) to prepare a paste (dispersion). Specifically, the dispersion medium as the polar solvent is water, alcohol, polyol, glycol ether, 1-methylpyrrolidinone, pyridine, terpineol, butyl carbitol, butyl carbitol acetate, texanol, phenoxypropanol, diethylene glycol monobutyl ether, diethylene glycol. Examples thereof include monobutyl ether acetate, γ-butyrolactone, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, methoxybutyl acetate, methoxypropyl acetate, diethylene glycol monoethyl ether acetate, ethyl lactate, 1-octanol and the like.

  An auxiliary substance that promotes lowering of the sintering temperature and adhesion can be added to the dispersion. The auxiliary substance may have a viscosity adjusting function. The auxiliary substance added at this time may be a water-soluble resin or an aqueous resin. Specifically, acrylic resin, maleic acid resin, fumaric acid resin, high acid value resin of styrene / maleic acid copolymer resin, polyester resin, polyolefin resin phenoxy resin, polyimide resin, polyamide resin or vinyl acetate emulsion, acrylic emulsion, Synthetic rubber latex, epoxy resin, phenol resin, DAP resin, urethane resin, fluorine resin, silicone resin, ethyl cellulose, polyvinyl alcohol, etc. can be added, and inorganic binders include silica sol, alumina sol, zirconia sol, titania sol It can be illustrated. However, excessive addition of the resin as an auxiliary substance is not preferable because it results in lowering the metal content relative to the entire dispersion. The amount is preferably about several parts by mass with respect to the total amount of metal.

  The following products are known that can be used as auxiliary substances. However, in the case of having the above-described properties, the use of anything other than those described in this column is not excluded. Examples of the acrylic resin include BR-102 resin manufactured by Mitsubishi Rayon Co., Ltd. and Alflon UC-3000 resin manufactured by Toagosei Co., Ltd. Examples of the polyester resin include Byron 220 manufactured by Toyobo Co., Ltd. and Marquide No. 1 manufactured by Arakawa Chemical Industries, Ltd. Examples of the epoxy resin include Adeka Resin EP-4088S manufactured by ADEKA Corporation and 871 manufactured by Japan Epoxy Resin Co., Ltd. Moreover, as a phenol resin, Gunei Chemical Industry Co., Ltd. resin top PL-4348 etc. can be illustrated. Examples of the phenoxy resin include 1256 manufactured by Japan Epoxy Resin Co., Ltd. and Tamanol 340 manufactured by Arakawa Chemical Industries, Ltd. Examples of the DAP resin include Dapp A manufactured by Daiso Corporation. Examples of the urethane resin include Millionate MS-50 manufactured by Nippon Polyurethane Industry Co., Ltd. Examples of ethyl cellulose include Etocel STANDARD4 manufactured by Nihon Kasei Co., Ltd. Examples of polyvinyl alcohol include Kuraray Co., Ltd. RS-1713.

  Moreover, since the metal nanoparticle of this invention is micro, it is easy to aggregate particles. Therefore, it is also preferable to add a dispersant to disperse the particles. Any commercially available general-purpose material may be used as long as it has an affinity for the particle surface and also has an affinity for the dispersion medium. In addition to a single type, a plurality of types of dispersants may be used in combination.

  Dispersants having such properties include fatty acid salts (soap), α-sulfo fatty acid ester salts (MES), alkylbenzene sulfonates (ABS), linear alkylbenzene sulfonates (LAS), alkyl sulfates (AS), Low molecular weight anionic (anionic) compounds such as alkyl ether sulfate (AES) and alkyl sulfate triethanol, fatty acid ethanolamide, polyoxyethylene alkyl ether (AE), polyoxyethylene alkyl phenyl ether (APE), sorbitol, Low molecular weight nonionic compounds such as sorbitan, low molecular weight cationic (cationic) compounds such as alkyltrimethylammonium salt, dialkyldimethylammonium chloride, alkylpyridinium chloride, Low molecular amphoteric compounds such as in, sulfobetaine, lecithin, formalin condensate of naphthalene sulfonate, polystyrene sulfonate, polyacrylate, copolymer salt of vinyl compound and carboxylic acid monomer, carboxymethyl cellulose Typical examples are polymer aqueous dispersants such as polyvinyl alcohol, polymer non-aqueous dispersants such as polyacrylic acid partial alkyl esters and polyalkylene polyamines, and polymer cationic dispersants such as polyethyleneimine and aminoalkyl methacrylate copolymers. It is a typical one. However, as long as it is suitably applied to the particles of the present invention, those having a structure other than the ones exemplified here are not excluded.

  Specific examples of the dispersants are as follows. However, in the case where the dispersant has the above-mentioned properties, the use of a dispersant other than those described in this section is not excluded. For example, Sanyo Chemical Co., Ltd., Viewlight LCA-H, LCA-25NH, etc., Kyoeisha Chemical Co., Ltd., Floren DOPA-15B, etc., Nippon Lubrizol Corporation Solplus AX5, Solsperse 9000, Sol Six 250, etc. EFKA4008 manufactured by Kaadi Dives, Ajispar PA111 manufactured by Ajinomoto Fine-Techno Co., Ltd., TEXAPHOR-UV21 manufactured by Cognix Japan Co., Ltd. Disparon 1751N, Hiprad ED-152, etc. Neos FTX-207S, Footage 212P, etc. Toagosei Co., Ltd. AS-1100, etc., Kao Corporation Causera 2000, KDH-154, MX-2045L, Homogenol L-18, Rheodor SP-010V, etc., Epan U103, Cyanol DC902B, Neugen EA-167, Prisurf A219B, etc. made by Daiichi Kogyo Seiyaku Co., Ltd. Megaface F-477, Sylface SAG503A manufactured by Nissin Chemical Industry Co., Ltd., Dinol 604, SN Spurs 2180 manufactured by San Nopco Co., Ltd., SN Leveler S-906, etc. S-386 manufactured by AGC Seimi Chemical Co., Ltd. Can be illustrated.

  When an additive such as an auxiliary substance or a dispersing agent is added, the amount may be 10% by mass or less, preferably 5% by mass or less, and more preferably 3% by mass or less, based on the total amount of metal contained in the paste. If the addition amount is less than 0.1% by mass, the addition effect is not obtained, and the nanoparticles aggregate in the solution, which is not preferable. In addition, since the addition effect is no longer improved by adding 10% by mass or more, the upper limit is appropriately about 10% by mass.

  In addition, an appropriate mechanical dispersion treatment can be used when preparing the dispersion. Any known method can be employed under the condition that the mechanical dispersion treatment does not involve significant modification of particles. Specific examples include ultrasonic dispersion, a disper, a three-roll mill, a ball mill, a bead mill, a twin-screw kneader, and a self-revolving stirrer, and these can be used alone or in combination.

  Next, the joining method using the joining material of the present invention will be outlined. A bonding material is applied to the bonding portion with a thickness of about 20 to 200 μm by various printing methods such as a metal mask, a dispenser, or a screen printing method. Unlike ordinary adhesives and solders, the bonding material of the present invention becomes a metal having the same melting point as that of the bulk after sintering, so that it is not necessary to make the bonding interface thin. This is because the bonding layer has a hardness equal to or higher than that of the bulk metal.

  However, since the bonding material of the present invention is coated or bonded to the surface of the metal nanoparticles with an organic compound, gas is generated when these organic compounds are desorbed or decomposed. In FIG. 1, the joining process at the time of using the joining material of this invention is shown typically. FIG. 1A shows a state in which the bonding material 3 is applied between the bonding objects 1 and 2. In addition, the thin film layer for improving the wettability with this joining material may be formed in the surface of a joining target object. The thin film layer can also be formed by, for example, plating, vapor deposition, or sputtering.

  When heat is applied thereto, gas generated by decomposition of the organic compound in the bonding material 3 is generated as bubbles 4. (See FIG. 1 (b)). If a bonding layer is formed between the bonding objects 1 and 2 while leaving the bubbles, the strength of the bonding layer is lowered. In addition, there is a concern that such bubbles remain in the metal phase to increase the amount of remaining carbon. Therefore, by heating the object to be joined while applying pressure 5, these gases are expelled (see FIG. 1 (c)), and a joining layer 6 in a bulk state is formed between the objects to be joined (FIG. 1 (d). )reference). This bulk bonding layer 6 exhibits high adhesion and bonding strength.

  In this case, it is sufficient to simply apply a load from above and below, but if pressure is applied from above and below while rotating, bubbles easily escape and adhesion is improved. In this case, a gas escape path may be formed at one of the end portions of the pressing surface.

  Further, the higher the pressure at this time, the better. However, in the present invention, it is not necessary to pressurize more than necessary. This is because the organic compound covering the surface is easily decomposed and converted into a metal by adopting the particle structure as in the present invention. When the joining object is a metal, sufficiently high joining strength is exhibited at about 5 MPa.

  Next, a preliminary firing step is performed. The purpose of this is to evaporate the solvent of the paste-like bonding material. However, since the organic compound on the surface of the metal nanoparticles may be decomposed and sintered, it is preferable to set the decomposition temperature or lower. In addition, since the decomposition temperature itself of an organic compound can be easily confirmed by TG (Thermogravimetry) measurement, it is desirable to measure the decomposition temperature in advance. In the pre-baking step of the metal nanoparticles, heating is performed at a temperature equal to or lower than the sintering temperature of the particles while applying pressure to the materials to be bonded. Specifically, it is preferably 150 ° C. or lower, more preferably 100 ° C. or lower. Although the holding time depends on the area of the bonded portion, it may be about 10 minutes, or may be about 30 seconds. Note that the pre-baking performed while applying pressure is the first heating step. Although it is referred to as “pressurization” here, the pressure to be applied is sufficient to fix the object to be joined so that it does not move. Therefore, it is sufficient that it is fixed so that it does not move. This “pressurization” itself may not be necessary.

  A temperature raising step may be provided between the preliminary firing step and the main firing step. At this time, the temperature rising rate is preferably in the range of 0.01 to 5 ° C./s.

  Next, a main baking process is performed. The main baking step is held at a temperature of 200 ° C. or higher and 400 ° C. or lower for about 10 minutes while applying pressure in some cases. Thus, the time for the main baking can be shortened by separating the preliminary baking step and the main baking step. The firing time is 60 minutes or less, depending on the area of the joined portion, 5 to 10 minutes or less, and even a short time such as 30 seconds, sufficient joining strength can be obtained. In addition, this baking process corresponds to a 2nd heating process.

  Next, an evaluation method for the bonding material of the present invention will be described.

<Evaluation of average primary particle size>
2 parts by mass of the washed metal nanoparticles were added to a mixed solution of 96 parts by mass of cyclohexane and 2 parts by mass of oleic acid and dispersed by ultrasonic waves. The dispersion solution was dropped on a Cu microgrid with a support film and dried to obtain a TEM sample. Using the transmission microscopic microscope (JEOL Co., Ltd. JEM-100CXMark-II type | mold), the image which observed the particle | grains in the bright field with the acceleration voltage of 100 kV was image | photographed by the magnification of 300,000 times. .

  For the calculation of the average primary particle size, image analysis software (A Image-kun (registered trademark) manufactured by Asahi Kasei Engineering Co., Ltd.) was used. This image analysis software identifies individual particles based on color shading. For a 300,000-fold TEM image, the “particle brightness” is “dark”, the “noise removal filter” is “present”, “ The circular particle analysis was performed under the condition that the “circular threshold” was “20” and the “overlap degree” was “50”, primary particles were measured for 200 or more particles, and the number average diameter was measured. In addition, when there were many condensed particles and irregular shaped particles in the TEM image, it was determined that measurement was impossible.

<Evaluation of bonding strength>
The strength of joining was performed in accordance with the method described in “Lead-free solder test method, Part 5: Tensile and shear test methods of solder joints” of JISZ-03918-5: 2003. In other words, this is a method of calculating the force when the bonded surface breaks while pressing the die-bonded object in the horizontal direction and resisting the pressed force. The test piece was performed using a 2 mm square copper chip. In this example, the test was performed using a bond tester manufactured by DAGE. The share height was 200 μm, the test speed was 5 mm / min, and the measurement was performed at room temperature.

  Moreover, the joining sample was produced using the same joining material and joining object. And the joining strength was measured by the said method, and average joining strength and its standard deviation (joining strength standard deviation) were computed. Moreover, CV value (%) was calculated | required so that the dispersion | variation in joining strength might not be influenced by the level of average joining strength. Specifically, it was calculated by the calculation of bonding strength standard deviation / average bonding strength × 100.

  Hereinafter, the performance of the bonding material of the present invention will be described using the results of the examples. Hereinafter, the case where silver is used as the metal species will be described.

<Preparation of silver nanoparticles>
Silver nanoparticles commonly used in this example were produced as follows. A 5 L reaction vessel was used as the reaction vessel. In addition, a stirring bar with a blade was installed at the center of the reaction tank for stirring. A thermometer for monitoring the temperature was installed in the reaction tank, and a nozzle was provided so that nitrogen could be supplied to the solution from the bottom.

  First, 3400 g of water was placed in the reaction tank, and nitrogen was passed from the lower part of the reaction tank at a flow rate of 3000 mL / min for 600 seconds in order to remove residual oxygen. Then, it supplied at the flow volume of 3000 mL / min from the reaction tank upper part, and made the nitrogen atmosphere in the reaction tank. And temperature adjustment was performed, stirring so that the solution temperature in a reaction tank might be 60 degreeC. Then, 7 g of ammonia water containing 28% by mass as ammonia was added to the reaction vessel, and then stirred for 1 minute in order to make the solution uniform.

  Next, 45.5 g of hexanoic acid (manufactured by Wako Pure Chemical Industries, Ltd.) (a molar ratio of 1.98 with respect to silver) was added as a protective agent, and the mixture was stirred for 4 minutes to dissolve the protective agent. Thereafter, 23.9 g (corresponding to 4.82 equivalents of silver) of a 50% by mass hydrazine hydrate (manufactured by Otsuka Chemical Co., Ltd.) aqueous solution as a reducing agent was added to obtain a reducing agent solution.

  A silver nitrate aqueous solution prepared by dissolving 33.8 g of silver nitrate crystals (manufactured by Wako Pure Chemical Industries, Ltd.) in 180 g of water was prepared in another container, and this was used as a silver salt aqueous solution. An amount of 0.00008 g of copper nitrate trihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) (corresponding to 1 ppm with respect to silver in terms of copper) was further added to the aqueous silver salt solution. In addition, since this addition amount is an amount that cannot be measured with a general-purpose weighing balance, the addition of this copper nitrate trihydrate produces a copper nitrate trihydrate aqueous solution with a high concentration to some extent. The diluted solution was added so that copper would enter the target addition amount. Further, the temperature of the silver salt aqueous solution was adjusted to 60 ° C., the same as the reducing agent solution in the reaction vessel.

  Thereafter, the aqueous silver salt solution was added to the reducing agent solution and mixed to start a reduction reaction. At this time, the color of the slurry finished changing in about 10 seconds from the start of the reduction reaction. Stirring was performed continuously and aged for 10 minutes in that state. Thereafter, the stirring was stopped, solid-liquid separation by suction filtration, washing with pure water, and drying at 40 ° C. for 12 hours to obtain fine silver particle powder. The silver ratio in the powder at this time was calculated as 97% by mass from the confirmation test of the remaining amount by heating. The balance is considered to consist of hexanoic acid or its derivative.

  In this example, not only hexanoic acid, which is a saturated fatty acid, but also sorbic acid, which is an unsaturated fatty acid, was used as a protective agent. Specifically, when producing the silver nanoparticles described above, the protective agent was changed to hexanoic acid to make 44.78 g of sorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.), and copper was not added. Obtained fine silver particle powder in the same manner as in the case of hexanoic acid. The silver ratio of the powder at this time was calculated as 99% by mass. The balance is thought to consist of sorbic acid or its derivatives.

Example 1
As metal nanoparticles, 45 g of hexanoic acid-coated silver particle powder (average primary particle size: 13.9 nm) obtained above and spherical silver particle powder (average particle size (D ₅₀ ) 600 nm, as metal submicron particles, particles Was confirmed by SEM, and the particles in the field of view were confirmed as independent particles 45 g, terpineol (mixed structural isomers / manufactured by Wako Pure Chemical Industries, Ltd.) 8.57 g, and DispersBYK (wetting dispersant) (Registered Trademark) -2020 (manufactured by Big Chemie Japan Co., Ltd.) 1.43 g was mixed to prepare a bonding material. The obtained bonding material was applied onto a solid copper material by a printing method. The condition at this time was a metal mask (mask thickness 50 μmt), and the metal squeegee was manually performed.

  Thereafter, heating was performed at 100 ° C. for 10 minutes in an air atmosphere as a preliminary baking step. From 100 ° C. to the main baking temperature (350 ° C.), the temperature was increased at a rate of 3.0 ° C./s, and when the temperature reached 350 ° C., the main baking step was performed for 5 minutes. In this example, a bonding layer having a metallic luster with no uneven baking was obtained.

  A joining test between an oxygen-free copper substrate and a copper chip was performed with the joining material of this example. The joining material of this invention was apply | coated to the lower part of a metal piece, and it has arrange | positioned on the copper substrate. Then, while pressurizing the oxygen-free copper substrate and the copper chip at a pressure of 2.5 MPa, a pre-baking step at 100 ° C. for 10 minutes in air and a main baking step at 350 ° C. for 5 minutes were performed to form a joined body. . In addition, it heated up with the temperature increase temperature of 3.0 degreeC / s between the preliminary baking process and this baking process. Table 1 shows the paste viscosity, the silver content, the value of the obtained bonding strength, and the like.

(Examples 2 to 4)
The metal nanoparticles were prepared in the same manner as in Example 1 except that they were changed to sorbic acid (average primary particle size: 58.8 nm) -coated silver particles and blended under the conditions shown in Table 1. The obtained results are also shown in Table 1.

(Example 5)
The same procedure as in Example 3 was performed except that the material to be joined was changed from a solid copper material to a silver-plated copper material.

(Examples 6 to 7)
Example 5 was repeated except that the dispersants were changed to Beaulite LCA-H (Example 6) and LCA-25NH (Example 7), respectively. The results obtained are shown in Table 1.

(Comparative Examples 1-2)
It was produced in the same manner as in Example 1 except that the hexanoic acid (sorbic acid in Comparative Example 2) -coated silver particle powder, terpineol, and the amount of the dispersant were 90: 8.57: 1.43 by mass ratio. The obtained results are also shown in Table 1.

(Comparative Example 3)
It was produced in the same manner as in Example 1 except that spherical silver particle powder having an average particle size (D ₅₀ ) of 600 nm, terpineol, and the amount of the dispersant were changed to 90: 8.57: 1.43 by mass ratio. The obtained results are also shown in Table 1.

  In this example, a bonding material was applied to the bonding surfaces of the objects to be bonded and heated while being pressurized. However, bubbles formed by decomposition of organic compounds and the like can be driven out when the sintered metal nanoparticles are melted. Therefore, a bonding material may be applied to the bonding surfaces of the objects to be bonded, pre-baked without applying pressure, and after the bonding surfaces have dried, the bonding surfaces may be butted together and heated.

  Examples 1 to 4 in which the paste according to the present invention was applied to a solid copper material, the bonding strength was 39.43 to 78.40 MPa, and the CV value representing variation was 3.47 to 17.24%. In Examples 5 to 7 in which the members were bonded to a member obtained by silver-plating a solid copper material, the bonding strength was 70.40 to 105.80 MPa, and the CV value was 6.01 to It was shown that it was possible to form a very good joined body of 12.10%.

  Since the comparative example 3 does not contain metal nanoparticles, the particles are not melted at a temperature of about the main firing, the bonding strength is low, and it cannot be said that the objects to be bonded are bonded. In Comparative Examples 1 and 2, the average bonding strength showed a value close to that of Example 1, but the variation in bonding strength between samples (CV value) was large. In Comparative Examples 1 and 2, the metal submicron particles were not contained, and it was considered that the cause was that the gas between the junctions could not be released due to the pressurization during the pre-firing.

  In Example 1 and Example 3, the content ratio of metal nanoparticles and metal submicron particles is the same, but the organic compound covering the metal nanoparticles is different from hexanoic acid and sorbic acid. The bonding strength was higher in Example 3, and the variation in bonding strength (CV value) was smaller in Example 3.

  Further, Example 2 and Example 4 are the same in that the organic compound that coats the metal nanoparticles is sorbic acid, but the content ratio of the metal nanoparticles and the metal submicron particles is different. Example 4 having a higher content ratio of metal submicron particles had higher bonding strength and lower variation (CV value).

  Looking at the trends of these four samples, the lower the paste viscosity, the higher the average bonding strength and the smaller the variation (CV value). That is, stronger and more stable bonding was possible. The variation in bonding strength is considered to depend on the degree to which the gas generated in the bonding layer escapes, so it can be determined that the lower the paste viscosity, the more reliable the degassing.

  Of course, when Example 1 and Comparative Example 2 were compared, the average joint strength of Comparative Example 2 having a low paste viscosity was smaller than that of Example 1, and the CV value was large. From this, the strength of the average bonding strength and the low variation (CV value) do not depend solely on the viscosity. That is, Examples 1 to 7 which are the bonding materials of the present invention, due to the synergistic effect of the content ratio of the organic compound covering the metal nanoparticles and the metal nanoparticles and the metal submicron particles, which affects the viscosity of the paste, It is believed to have a high average bond strength and a low CV value.

  FIG. 2 shows the relationship between viscosity and average bonding strength. The vertical axis represents average bonding strength (MPa), and the horizontal axis represents paste viscosity. White squares are Comparative Examples 2 and 3. Since the viscosity of Comparative Example 1 was so high that the paste viscosity could not be measured, it was not plotted. Black diamonds are Examples 1 to 4, and black circles are Examples 5 to 7. Example 5 and Example 3 are the same paste (thus the paste viscosity is the same), but the difference is whether the treated surface of the object to be joined is silver-plated or pure copper. Referring to Example 5 (black circle) and Example 3, when the surface to be treated was plated with silver, the bonding strength was increased. Moreover, although both Example 6 (black circle) and 7 (black circle) are samples in which the treated surface of the bonded surface is subjected to silver plating, high bonding strength was exhibited even when the paste viscosity increased.

  In Examples 1 to 4, as described above, the tendency of the average bonding strength to increase as the paste viscosity decreased was also confirmed in the graph. In Examples and Comparative Examples, the amounts of the dispersion medium and the silver content are almost the same, so the difference in viscosity is not due to the difference in the solvent content. Therefore, when the constituent ratio of the nanoparticles and the submicron particles was compared, in Examples 2 to 4, the paste viscosity decreased as the constituent ratio of the submicron particles increased. Specifically, when the nanoparticles / submicron particles became 9.00, 1.00, and 0.25, the paste viscosity decreased to 112.1, 34.4, and 11.5 (unit: Pa · s). . In addition, although the composition ratio of Example 1 nanoparticle and submicron particle is the same, since the nanoparticle coat | covers hexanoic acid, it is thought that the paste viscosity rose.

  Comparative Example 3 was a case where no nanoparticles were contained. The paste viscosity is relatively low at 22.8 Pa · s, but the average joint strength is very low at 2.73 MPa. That is, when no nanoparticles are contained at all, the sintering temperature becomes high, and it is considered that a temperature of about 350 ° C. cannot be used as a bonding material.

  The bonding material according to the present invention is a non-insulated semiconductor device, application to bare chip mounting assembly technology, power device (rectifier diode, power transistor, power MOSFET, insulated gate bipolar transistor, thyristor, gate turn-off thyrist, triac bonding) It can also be applied to processes, and can also be used as a bonding material on glass whose surface is chrome-treated, and can also be used as a bonding material for electrodes and frames of lighting devices using LEDs.

1, 2 Bonding object 3 Bonding material 4 Bubble 5 Pressure 6 Bonding layer

Claims (8)

Metal submicron particles having an average primary particle diameter (D50 diameter) of 0.5 to 3.0 μm, an average primary particle diameter of 1 to ₂₀₀ nm, and a carbon number of 6 A bonding material comprising metal nanoparticles coated with a fatty acid and a dispersion medium for dispersing them.   2. The bonding material according to claim 1, wherein a mass ratio of the metal component of the metal nanoparticles and the metal submicron particles (metal nanoparticle / metal submicron particle) is 0.1 to 10.0. The bonding material according to claim 1, wherein the fatty acid has at least one unsaturated bond.   The dispersant is contained in an amount of 0.5% to 2.5% by mass with respect to the total amount of the metal component of the metal nanoparticles and the metal component of the metal submicron particles. The bonding material described in 1.   The bonding material according to any one of claims 1 to 4, wherein a metal of the metal submicron particles and the metal nanoparticles is silver.   6. The bonding material according to claim 1, wherein the bonding material has a viscosity of 10 to 250 Pa · s (25 ° C., 5 rpm, C (cone): value at 35/2) at room temperature. The bonding material described.   A step of applying the bonding material according to any one of claims 1 to 6 to the bonding surface, and heating at a temperature equal to or lower than a sintering temperature of the metal nanoparticles while bonding an object to be bonded to the bonding surface. The joining method which has 1st heating process and the 2nd heating process of heating the said joining target object at the heating temperature of 200-400 degreeC.   The bonding method according to claim 7, wherein the heating time in the first and second heating steps is not less than 30 seconds and not more than 60 minutes.