JP5795096B2 - Silver paste excellent in low-temperature sinterability and method for producing the silver paste - Google Patents

Description

  The present invention relates to a metal paste in which silver particles are dispersed in a solvent. Specifically, it is a metal paste that essentially contains silver particles having a particle size of 100 to 200 nm, and can be sintered at a relatively low temperature of 150 ° C. or lower and can produce a low-resistance silver sintered body. Regarding paste.

  A metal paste in which conductive metal particles are kneaded and dispersed in a solvent as a solid content is used as a circuit forming material in printed electronics and as a conductive bonding material for bonding various semiconductor elements to a substrate. This metal paste is applied to a substrate or a member to be joined and then heated and fired to sinter the metal particles, thereby forming circuits / electrodes, joints / bonding portions.

  And it is metal paste which applies silver particle as a metal particle that attracts attention as a metal paste especially useful for the said use. Silver is a metal having a low specific resistance, and an appropriately formed sintered body can effectively act as a conductive film. In addition, silver has the advantage of excellent thermal conductivity, and the metal paste to which silver is applied can be used as a bonding material and heat conduction material for manufacturing semiconductor devices in which the operating temperature is increased due to the large current of power devices and the like. It is supposed to be effective.

  As a metal paste to which silver particles are applied, for example, Patent Document 1 includes silver nanoparticles having an average primary particle diameter of 1 to 200 nm and a dispersion medium having a boiling point of 230 ° C. or more, and further 0.5 to 3.0 μm. A bonding material comprising submicron silver particles of the following is described. The bonding material made of the metal paste described in Patent Document 1 has a bonding temperature (sintering temperature) for silver particle sintering of 200 ° C. or higher. This bonding temperature can be said to be lower than that of the brazing material, but it is difficult to say that the bonding temperature is sufficiently low. The level of the joining temperature is an element that can affect the semiconductor element that is the material to be joined, and it is desirable that the joining temperature be as low as possible.

  Here, regarding the sintering temperature of the metal particles, the possibility of adjustment by controlling the size (particle size) is known. This is referred to as a so-called nano-size effect, and is a phenomenon in which the melting point of the metal particles is remarkably lowered as compared with the bulk material when the nano-particles are tens of nanometers or less. The metal paste described in Patent Document 1 contains silver particles with a relatively large particle size of submicron size, so it is considered difficult to sinter at low temperatures. However, if this nanosize effect is used, sintering is performed at a lower temperature. It is believed that a possible metal paste can be obtained.

As nano-level silver particles, those produced by a thermal decomposition method of a silver complex according to Patent Document 2 have been reported. In the thermal decomposition method, a heat-decomposable silver compound such as silver oxalate (Ag ₂ C ₂ 0 ₄ ) is used as a raw material to react with an appropriate organic substance to form a precursor complex, which is heated to form silver particles. How to get. According to the thermal decomposition method, fine nano-level silver particles having an average particle diameter of a few nm to a few tens nm can be produced.

International Publication No. 2011/155615 Pamphlet JP 2010-265543 A

  However, according to the present inventors, it has been confirmed that there is a problem with the metal paste composed of the nano-level silver particles. Although nano-level silver particles are sintered at a low temperature of 200 ° C. or lower, the resistance value of the sintered body tends to be considerably higher than that of the bulk material. This problem greatly impairs the usefulness of the metal paste as a circuit material or a conductive bonding material.

  Therefore, the present invention can sinter silver particles in a low temperature range for a metal paste containing silver particles, and can form a sintered body with low resistance and a sintered body with excellent thermal conductivity. Offer things. In the present invention, a low temperature range of 150 ° C. or lower was set as the target value of the sintering temperature.

  The present invention for solving the above-mentioned problems is a metal paste obtained by kneading a solid content composed of silver particles and a solvent, wherein the solid content contains 30% or more of silver particles having a particle size of 100 to 200 nm based on the number of particles. Furthermore, the silver particle which comprises solid content is a metal paste which the amine compound with a total of 4-8 carbon atoms couple | bonded as a protective agent.

  The metal paste according to the present invention contains silver particles constituting a solid content kneaded with a solvent having a medium particle size range of 100 to 200 nm in a certain ratio or more. Further, these silver particles are obtained by binding a protective agent made of a specific amine compound. According to the present inventors, the possibility of sintering at low temperatures and the reduction in resistance of the sintered body, which are the problems of the present application, are to make the particle size range of the main silver particles within the above range, and to use an appropriate protective agent. Effectively achieved as a result of the combination with the selection. Hereinafter, the present invention will be described in more detail.

  In the metal paste according to the present invention, it is necessary that silver particles having a particle size of 100 to 200 nm are present in an amount of 30% or more on the basis of the number of particles with respect to the entire silver particles as a solid content. This is because such moderately fine silver particles contribute to low temperature sintering. It is preferable that all silver particles contained in the paste have a particle size of 100 to 200 nm, that is, a ratio of 100%, but this need not be the case. If silver particles having a particle size of 100 to 200 nm are 30% or more, particles outside this particle size range may be present. For example, even if it is a metal paste in which silver particles having a particle size of 100 to 200 nm and silver particles having a particle size of 20 to 30 nm are mixed, if the ratio of the silver particles having a particle size of 100 to 200 nm is 30% or more, 150 ° C. or less. Sintering is possible, and the resistance value of the sintered body is low. Further, a metal paste in which coarse silver particles having a particle diameter of more than 500 nm are mixed with silver particles having a particle diameter of 100 to 200 nm may be used. Usually, coarse silver particles exceeding 500 nm (0.5 μm) are not sintered at 200 ° C. or lower. However, when silver particles having a particle diameter of 100 to 200 nm applied in the present invention are present in a certain ratio or more, the entire silver particles including such coarse particles are sintered at a low temperature.

  As for the ratio of the number of silver particles having a particle size of 100 to 200 nm, if it is less than 30%, sintering does not occur at 150 ° C. or lower or is insufficient. Naturally, all the silver particles in the metal paste have a particle size of 100 to 200 nm, that is, those having a number ratio of 100%, have the effect of the present invention. As described above, in the present invention, silver particle groups having different particle diameters may be mixed while having a particle diameter of 100 to 200 nm as an axis, but the average particle diameter (number average) for all silver particles is , 60 to 800 nm is preferable.

  In the paste according to the present invention, the sinterability of silver particles having a particle size of 100 to 200 nm is also related to the action of a protective agent that binds to the silver particles. The protective agent is a compound that binds to a part or the whole surface of metal particles suspended in a solvent, and suppresses aggregation of the metal particles. In the present invention, the protective agent that binds to the silver particles is an amine compound having a total carbon number of 4 to 8.

  As a protective agent for silver particles, organic substances such as carboxylic acids are generally applicable in addition to amines, but the protective agent applied in the present invention is limited to amine compounds when a protective agent other than amine is applied. This is because sintering of silver particles at 150 ° C. or lower does not occur. In this regard, even if the silver particles have a particle size in the range of 100 to 200 nm, low-temperature sintering does not occur with a protective agent other than amine.

  In addition, the total number of carbon atoms of the amine compound as a protective agent is set to 4-8 because the carbon number of the amine affects the stability and sintering characteristics of the silver particles in relation to the particle size of the silver particles. Because. This is because it is difficult for an amine having less than 4 carbon atoms to stably present silver fine particles having a particle diameter of 100 nm or more, and it is difficult to form a uniform sintered body. On the other hand, amines having more than 8 carbon atoms tend to increase the stability of silver particles excessively and increase the sintering temperature. From these, the protective agent of the present invention is limited to amine compounds having 4 to 8 carbon atoms in total.

  Furthermore, the amine compound is preferably an amine compound having a boiling point of 220 ° C. or lower. Silver particles to which such a high-boiling amine compound is bonded are difficult to separate during sintering even if the particle size range is in an appropriate range, thus inhibiting the progress of sintering.

As the number of amino groups in the amine compound as the protective agent, (mono) amine having one amino group or diamine having two amino groups can be applied. Further, the number of hydrocarbon groups bonded to the amino group is preferably one or two, that is, primary amine (RNH ₂ ) or secondary amine (R ₂ NH) is preferable. And when applying diamine as a protective agent, the thing whose at least 1 or more amino group is a primary amine or a secondary amine is preferable. The hydrocarbon group bonded to the amino group may be a hydrocarbon group having a cyclic structure in addition to a chain hydrocarbon having a linear structure or a branched structure. Further, oxygen may be partially included. Preferable specific examples of the protective agent applied in the present invention include the following amine compounds.

  It is preferable that the protective agent made of the above-described amine compound is bonded to all the silver particles in the metal paste. In the present invention, silver particles having a particle size of 100 to 200 nm are essential, but it is allowed to mix silver particles having a particle size outside this range. Even when silver particles having such different particle size ranges are mixed, the silver particle protective agent having a particle size of 100 to 200 nm is naturally required to be the amine compound, but it is out of the range of 100 to 200 nm. The silver particles are required to have the amine compound protective agent bound thereto. However, the compounds are not necessarily the same, and different protective agents may be included as long as the total number of carbon atoms is 4 to 8 (for example, within the range shown in Table 1).

  And in the metal paste which concerns on this invention, in order to ensure low temperature sinterability, it is preferable that the amine compound which is a protective agent is contained in the quantity which is not excessive and insufficient, and has couple | bonded with the silver particle. When the amount of the protective agent is small, the protective effect on the silver particles is insufficient, and the silver particles agglomerate during storage and the low-temperature sinterability is impaired. Moreover, when a protective agent couple | bonds with silver particle excessively, there exists a possibility that the volume shrinkage of the silver sintered compact by amine loss | disappearance at the time of sintering may become large, and many cracks may generate | occur | produce in a sintered compact. Therefore, regarding the amount of the protective agent (amine compound) in the paste according to the present invention, the balance between the nitrogen concentration and the silver concentration in the paste is important. Specifically, the ratio of nitrogen concentration (mass%) to silver particle concentration (mass%) (N (mass%) / Ag (mass%)) is preferably 0.0003 to 0.003. If it is less than 0.0003, the protective effect on silver particles is insufficient, and if it exceeds 0.003, the sintered body may be cracked. The nitrogen concentration in the metal paste can be measured by elemental analysis (CHN analysis or the like) of the paste, and the silver particle concentration can be easily obtained from the mass of silver particles and the amount of solvent used during paste production.

  The silver particles combined with the silver particle protective agent described above are dispersed and suspended in a solvent to form a metal paste. As this solvent, an organic solvent having a carbon number of 8 to 16 and having an OH group in the structure and a boiling point of 280 ° C. or lower is preferable. This is because when the silver particle sintering temperature target is set to 150 ° C. or lower, it is difficult to volatilize and remove a solvent having a boiling point higher than 280 ° C. Preferred examples of this solvent include terpineol (C10, boiling point 219 ° C.), dihydroterpineol (C10, boiling point 220 ° C.), texanol (C12, boiling point 260 ° C.), 2,4-dimethyl-1,5-pentadiol ( C9, boiling point 150 ° C.) and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (C16, boiling point 280 ° C.). A plurality of solvents may be used as a mixture, or may be used alone.

  About the mixing ratio of the solvent and solid content (silver particle) in the whole paste, the solvent content is preferably 5% to 60% by mass ratio. If it is less than 5%, the viscosity of the paste becomes too high. If it exceeds 60%, it becomes difficult to obtain a sintered body having a required thickness.

  Next, the manufacturing method of the metal paste which concerns on this invention is demonstrated. The metal paste according to the present invention is produced by kneading a solid containing 30% or more of silver particles having a particle size of 100 to 200 nm in a solvent. And in order to manufacture solid content which consists of silver particles which contain 30% or more of silver particles having a particle size of 100 to 200 nm, it is required to manufacture silver particles while adjusting the particle size and particle size distribution.

Here, in this invention, the thermal decomposition method which used the silver complex as the precursor is employ | adopted as a manufacturing method of silver particle. The thermal decomposition method uses a silver compound having thermal decomposability such as silver oxalate (Ag ₂ C ₂ 0 ₄ ) as a starting material, and forms a silver complex with an organic compound that serves as a protective agent. Is heated to obtain silver particles. The thermal decomposition method is also a method applied in the above-mentioned Patent Document 2. The particle size adjustment is easier than other silver particle production methods such as a liquid phase reduction method (the method described in Patent Document 1), and comparatively grain size. Silver particles with a uniform diameter can be produced.

  However, according to the present inventors, the conventional pyrolysis method is suitable for the production of fine silver particles having an average particle diameter of several nanometers to several tens of nanometers. It was difficult to preferentially produce silver particles having a moderately large particle size range of 100-200 nm. The present inventors consider the generation mechanism of silver particles by the pyrolysis method, and adjust the amount of water in the reaction system when the silver complex is pyrolyzed to form silver particles, whereby silver having a particle size of 100 to 200 nm is obtained. The particles were preferentially manufactured.

  That is, the method for producing silver particles in the present invention is to produce a silver-amine complex as a precursor by mixing a silver compound having thermal decomposability and an amine, and heating the reaction system containing the precursor. In the method for producing silver particles, the water content of the reaction system before heating is set to 5 to 100 parts by weight with respect to 100 parts by weight of the silver compound.

In the silver particle production method of the present invention, the silver compound having thermal decomposability as a starting material is silver oxalate, silver nitrate, silver acetate, silver carbonate, silver oxide, silver nitrite, silver benzoate, silver cyanate, Silver citrate, silver lactate, etc. can be applied. Of these silver compounds, silver oxalate (Ag ₂ C ₂ O ₄ ) or silver carbonate (Ag ₂ CO ₃ ) is particularly preferable. Silver oxalate and silver carbonate can be decomposed at a relatively low temperature without requiring a reducing agent to produce silver particles. Further, since carbon dioxide generated by the decomposition is released as a gas, no impurities remain in the solution.

  Since silver oxalate is explosive in the dry state, water or an organic solvent (alcohol, alkane, alkene, alkyne, ketone, ether, ester, carboxylic acid, fatty acid, aromatic, amine, amide, nitrile Etc.) are preferably mixed and wetted. By making it wet, explosiveness is remarkably lowered and handling becomes easy. At this time, what mixed 5 to 200 weight part of dispersion solvents with respect to 100 weight part of silver oxalate is preferable. However, as described above, since the present invention strictly regulates the amount of water in the reaction system, the mixing of water needs to be within a range not exceeding the specified amount.

  The silver-amine complex serving as the precursor of the silver particles is produced by mixing and reacting the silver compound and the amine compound. As the amine used here, an amine compound having 4 to 8 carbon atoms in total is applied.

  The mixing amount of the amine compound is such that the ratio of the mass of the amine compound (protective agent) and the mass of silver in the silver compound (the mass of the amine compound (protective agent) / Ag mass) is 2 to 5, so that the amine compound is mixed. Adjust the amount. This is because a sufficient silver-amine complex is formed without generating an unreacted silver compound. Even if an excessive amine compound is bonded to the silver particles, it is removed by washing after the silver particles are produced.

  A silver-amine complex is formed by the reaction of the silver compound and the amine compound, and a reaction system for producing silver particles is formed. Thereafter, the reaction system is heated to produce silver particles. In the present invention, the amount of water in the reaction system is defined at this stage. It is considered that the water in the reaction system acts as a buffering agent that causes heating to proceed uniformly in the complex decomposition step. In the present invention, the buffering action of water is used to relax the temperature difference in the reaction system during heating, and promote nucleation and growth of silver particles while making them uniform.

  The water content of the reaction system needs to be in the range of 5 to 100 parts by weight with respect to 100 parts by weight of the silver compound. A preferable range of the water content is 5 to 95 parts by weight, and a more preferable range is 5 to 80 parts by weight. When the amount of water is small (less than 5 parts by weight), the silver particles obtained are mainly fine particles having a particle size of less than 100 nm, and the proportion of silver particles of 100 to 200 nm is reduced. On the other hand, when the amount of water is large (exceeding 100 parts by weight), the particle size variation of the silver particles becomes too large, and the ratio of the silver particles of 100 to 200 nm tends to decrease.

  The water content of the reaction system is the water content immediately before the heating step, and it is necessary to consider the amount of water added to the reaction system so far. As described above, when silver oxalate is applied as the silver compound, it may be used in a wet state in which water has been added in advance. The amount of water added in advance is also included in the amount of water. For this reason, when only the amount added in advance to the silver compound or the homogenizing agent falls within the specified range of the water content, it can be heated as it is without separately adjusting the water content of the reaction system. On the other hand, if the amount added in advance is less than the lower limit (5 parts by weight) of the water content, it is necessary to adjust the amount of water, such as adding water separately. The timing of adding water may be before the heating step, and may be added at any stage before formation of the silver-amine complex or after formation of the complex.

  In the present invention, it is sufficient that the reaction system is composed of a silver-amine complex and an appropriate range of moisture, and silver particles having a suitable particle size range can be produced without other additives. However, adjustment of the particle size distribution (increase in the proportion of silver particles of 100 to 200 nm) and addition of additives for further stabilization of the silver complex are not excluded depending on the relationship of the amine compound used. .

  The additive applicable in the present invention is a homogenizing agent for adjusting the particle size distribution. This homogenizing agent is an organic compound represented by Chemical Formula 1 having an amide as a skeleton. This homogenizing agent makes the particle size of the silver particles uniform by making the stability of the silver-amine complex in the reaction system uniform and by aligning the timing of nucleation and growth when silver particles are produced by complex decomposition. Additives to align.

An organic compound that functions as a homogenizing agent is required to have an amide (carboxylic amide) (N—C═O) in its skeleton. In the amide substituent (R, R ′, R ″), R represents hydrogen, hydrocarbon, aminoalkyl or an amino group comprising a combination thereof, and R ′, R ″ represents hydrogen or hydrocarbon. Can be applied. According to the present inventors, the amide of the organic compound, which is a homogenizing agent, acts on the amine moiety of the silver-amine complex and the complex is stabilized. Specific examples of the organic compound as the homogenizing agent include urea, urea derivatives, N, N-dimethylformamide (DMF: (CH ₃ ) ₂ NCHO), N, N-diethylformamide (DEF: (C _{2 H 5) 2 NCHO),} N, N- dimethylacetamide _{(C 4 H 9 NO),} N, N- dimethyl-propionamide _{(C 5 H 11 NO),} N, N- diethylacetamide _{(C 6} H 13 NO) Etc. Examples of urea derivatives include 1,3-dimethylurea (C ₃ H ₈ N ₂ O), tetramethylurea (C ₅ H ₁₂ N ₂ O), 1,3-diethylurea (C ₅ H ₁₂ N ₂ O), and the like. Is mentioned.

When the homogenizing agent is added to the reaction system, the amount is the ratio of the number of moles of the homogenizing agent (mol _{homogenizing agent} ) to the number of moles of silver (mol _Ag ) in the silver compound (mol _{homogenizing agent} / mol _Ag ). Therefore, it is preferably 0.1 or more. When a plurality of organic compounds are used simultaneously as the homogenizing agent, the total addition amount is preferably 0.1 or more. If the molar ratio is less than 0.1, the effect is difficult to occur. On the other hand, the upper limit of the molar ratio (the upper limit of the homogenizing agent) is not particularly specified, but is preferably 4 or less with respect to silver of the silver compound in consideration of the purity of the silver particles. The homogenizing agent is preferably added as it is in the case of a liquid organic compound. Further, in the case of a solid compound such as urea, it may be added as a solid or may be added as an aqueous solution. However, when the aqueous solution is used, it is necessary to consider the water content of the reaction system.

  Then, the water content of the reaction system is confirmed, and after adding an additive as necessary, silver particles are precipitated by heating the reaction system. It is preferable that the heating temperature at this time be equal to or higher than the decomposition temperature of the silver-amine complex. As described above, the decomposition temperature of the silver-amine complex varies depending on the type of amine coordinated to the silver compound, but in the case of the silver complex of the amine compound applied in the present invention, the specific decomposition temperature is 90 to 130 ° C.

  In the heating step of the reaction system, the heating rate affects the particle size of the precipitated silver particles, and therefore the particle size of the silver particles can be controlled by adjusting the heating rate of the heating step. Here, it is preferable to adjust the heating rate in a heating process in the range of 2.5-50 degreeC / min to the set decomposition temperature.

  Silver particles precipitate through the above heating process. The precipitated silver particles are recovered through solid-liquid separation and become a solid content of the metal paste. What is important here is that washing is performed so that excessive amine compounds do not bind to the recovered silver particles. As described above, in the present invention, it is preferable to make the binding amount of the amine compound to the silver particles (the nitrogen content in the paste) appropriate. Therefore, it is necessary to leave the minimum amine compound necessary for protecting the surface of the silver particles and to remove the excess amine compound from the system. Therefore, in the present invention, it is important to wash the precipitated silver particles.

  For the washing of the silver particles, it is preferable to apply an alcohol having a boiling point of 150 ° C. or lower such as methanol, ethanol, propanol or the like as a solvent. And as a detailed method of washing | cleaning, after adding a solvent to the solution after silver particle synthesis | combination and stirring until it suspends, it is preferable to remove a supernatant liquid by decantation. The amount of amine removed can be controlled by the volume of solvent added and the number of washings. When the above-described series of cleaning operations is performed once, it is preferable to use a solvent having a volume of 1/20 to 3 times that of the solution after silver particle synthesis and to wash 1 to 5 times.

  The recovered silver particles can be made into a metal paste by kneading with an appropriate solvent as a solid content. As the solvent, those described above can be applied. In addition, the production of silver particles by the above process is performed in two or more systems, and a mixture of two or more kinds of silver particles produced by them is used as a solid content, which is kneaded with a solvent to produce a metal paste. Also good.

  The metal paste containing silver particles with controlled particle size according to the present invention can be sintered even at a low temperature range of 150 ° C. or lower, and the resulting sintered body exhibits a low resistance value equivalent to that of bulk silver. . The metal paste according to the present invention can be applied as a conductive bonding material, and is also useful as a bonding material for electrical devices that handle large currents such as power devices.

The figure explaining the silver particle manufacturing process in this embodiment. The SEM photograph which shows the form of the silver particle manufactured by this embodiment. The figure which shows the particle size distribution of the metal paste manufactured by this embodiment. The figure which shows the result of the DTA analysis of the metal paste manufactured by this embodiment. The photograph which shows the form change of the sintering process of the metal paste manufactured by this embodiment. The photograph which shows the microscopic structure of the sintered compact of the genus paste manufactured by this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described. In the present embodiment, silver particles are produced while changing various conditions such as a silver compound as a raw material and an amine compound as a protective agent, and after kneading with a solvent to produce a metal paste, its thermal analysis and sintering characteristics And the resistance of the sintered compact was evaluated. The outline of the manufacturing process of the silver particle in this embodiment is shown in FIG. 1, and the manufacturing process of a silver particle is demonstrated.

Production of Silver Particles In this embodiment, 1.41 g of silver oxalate or 1.28 g of silver carbonate was used as a raw material silver compound so that the silver content was 1 g. When these silver compounds are used as they are, they are moistened by adding 0.3 g of water (21 parts by weight with respect to 100 parts by weight of silver oxalate and 23 parts by weight with respect to 100 parts by weight of silver carbonate). I prepared something in a state.

  And various amine compounds were added to the silver compound as a protective agent, and the silver-amine complex was manufactured. The silver compound and amine were mixed at room temperature and kneaded until creamed. Next, the produced silver-amine complex was added in combination with a urea solution and DMF as a homogenizing agent. In consideration of the amount of water, water was sometimes added. And the water content of the reaction system was checked before heating. In addition, about the protective agent, the example which applied oleic acid as things other than an amine is also prepared.

  About the reaction system by which the moisture content was confirmed, it heated from room temperature, the silver-amine complex was decomposed | disassembled, and silver particle was deposited. The heating temperature at this time assumed 110-130 degreeC as a decomposition temperature of a complex, and made this the ultimate temperature. The heating rate was 10 ° C./min.

  In the heating process, generation of carbon dioxide was confirmed from around the decomposition temperature. Heating was continued until the generation of carbon dioxide stopped to obtain a liquid in which silver particles were suspended. After precipitation of silver particles, methanol was added to the reaction solution for washing, and this was centrifuged. This washing and centrifugation were performed twice.

  Regarding the above silver particle production process, the following 12 types of silver particles were produced in this embodiment. Moreover, the SEM photograph of the silver particle manufactured in FIG. 2 is shown.

Production of Metal Paste Based on the 12 kinds of produced silver particles, a single or a plurality of silver particles were combined to obtain a solid content, and texanol was kneaded as a solvent to produce a metal paste. The ratio of solid content at this time is 80-95 mass%. About the manufactured metal paste, it sampled suitably and observed SEM and measured the particle size distribution. Moreover, N content was measured by CHN elemental analysis and ratio (N mass% / Ag mass%) with silver content was computed.

Low-temperature sintering test The metal paste produced above was sintered at a low temperature, and the presence / absence of sintering, electrical resistance of the sintered body, and adhesion (bonding force) were evaluated. In this low-temperature sintering test, 50 mg of each metal paste was applied to a Si substrate (with gold plating) (targeted to a film thickness of 50 μm), the temperature was raised to 150 ° C. at a rate of 2 ° C./min, and the temperature was increased to 150 ° C. At that stage, it was held for 2 hours and sintered. The sintered body was evaluated by first observing SEM and evaluating the presence or absence of the sintered body formation, and then measuring the volume resistivity. Furthermore, a peel test for evaluating adhesion was performed. In the peel test, 10 × 10 (100 matrix) incisions were made in the sintered body with a cutter, and then the adhesive tape was applied to the sintered body and then peeled off at once. I counted. As an evaluation criterion, the case where the residual rate was 95% to 100% was evaluated as good adhesion (◯), and the lower ratio was evaluated as poor adhesion (×). Table 3 shows the analysis results and low-temperature sintering test results for the metal paste manufactured in this embodiment. FIG. 3 shows the results of pastes c, f, i, and k as examples of the particle size distribution measurement results.

  From Table 3, if only considering low-temperature sinterability at 150 ° C., metal pastes a, b, and c having a particle size ratio of 100 to 200 nm and an average particle size of 20 to 30 nm are easily obtained. Sintered. On the other hand, metal pastes m, n, and o that tend to have a large average particle size are difficult to sinter. From these results, it can be said that there is a temporary correlation between the particle size and the sintering temperature. However, although the metal pastes a to c form a sintered body, the resistance value is high and the adhesion is inferior. Moreover, although sintered, many cracks were generated in the sintered body and there were some powdered portions. Regarding the resistance value, it is considered that the resistance is larger than the resistance value (1.6 μΩ · cm) of the bulk silver due to the voids called cracks. In addition, the influence of the presence of cracks can be considered on the adhesion, but in the first place, it is considered that the metal paste mainly composed of these fine silver particles is not sufficiently sintered (details will be described later). This will be explained by the results of thermal behavior studies). From these results, it can be said that it is not preferable to discuss only the average particle size in order to achieve both low-temperature sinterability of silver particles and low resistance of the sintered body.

  On the other hand, metal pastes (d to f, h, j to l) that appropriately contain silver particles having a suitable particle size (particle size of 100 to 200 nm) and that have suitable protective agents have good low-temperature sinterability. There were no cracks. And resistance value is also a value close | similar to silver of a bulk body, and adhesiveness is also favorable. Therefore, it can be said that these metal pastes were rapidly sintered even in a low temperature range of 150 ° C.

  In addition, although the silver particle ratio with a particle size of 100-200 nm is suitable for the metal paste g, since the hydroxyethylaminopropylamine (boiling point: 250 degreeC) whose boiling point exceeds 220 degreeC was applied, sinterability at low temperature is It can be said that it is inferior. Further, regarding the metal paste i to which oleic acid was applied instead of an amine compound as a protective agent, low-temperature sintering could not be performed although the ratio of silver particles having a particle size of 100 to 200 nm was suitable.

Analysis of thermal behavior In the low-temperature sintering test described above, the metal paste (a to c) mainly composed of fine silver particles (particle size 20 to 30 nm) is sintered, but a large number of cracks are generated in the sintered body. It was confirmed that the adhesion was also poor. On the other hand, the metal paste mainly composed of particles having a particle diameter of 100 to 200 nm of the present invention produced no problems and no cracks. Here, it was decided to conduct an analysis to confirm the difference in thermal behavior of each metal paste and the crack generation mechanism.

  By the way, regarding the analysis of the thermal behavior of the metal paste, the thermal history (held at 150 ° C. for 2 hours) performed in the low-temperature sintering test is close to the actual usage of the metal paste, but there is no change in the heating temperature. Not suitable for analysis of thermal behavior. Therefore, in the present embodiment, TG-DTA analysis (differential thermal analysis) for heating the metal paste at a constant temperature increase rate was performed to confirm the number of exothermic peaks and the generated temperature due to the sintering of the silver particles. In the DTA analysis of this metal paste, the rate of temperature rise is preferably 5 ° C./min to 20 ° C./min. In this embodiment, the measurement temperature range was from room temperature to 500 ° C., and the measurement was performed at a rate of temperature increase of 10 ° C./min.

  And when TG-DTA analysis was performed about each metal paste, it turned out that it can group into the number of the exothermic peak resulting from sintering of silver particle, and a generation | occurrence | production position (generation temperature). In other words, the number of exothermic peaks could be distinguished from one or two. Further, the generated temperature could be distinguished at 200 ° C. as a boundary. Among the DTA curves measured this time, FIG. 4 shows DTA curves of pastes c, f, i, and m as a representative example. Table 4 shows the number of exothermic peaks due to the sintering of silver particles and the measurement results of the generated temperature for the DTA curve measured for each metal paste.

  According to the DTA analysis, the metal paste (ac) mainly composed of fine silver particles having a particle diameter of 20 to 30 nm has an exothermic peak below 200 ° C. (180 ° C., 190 ° C.), and more than 200 ° C. ( Even at 210 ° C. and 230 ° C., an exothermic peak appears. Naturally, the exothermic peak at low temperature is expected in these metal pastes, which are considered to be sintered at low temperature due to the nanosize effect. However, a plurality of exothermic peaks appear in this way because the sintering behavior of fine silver particles proceeds in multiple stages.

  In contrast to this, it can be said that the metal paste (d to f, h, j to l) mainly composed of particles having a particle diameter of 100 to 200 nm according to the present invention exhibits a characteristic behavior in the result of DTA. That is, in this metal paste, only one exothermic peak derived from the silver particle sintering of the DTA curve appears in a temperature range of less than 200 ° C. (180 ° C., 190 ° C.). The occurrence of only one exothermic peak indicates that the silver particles are completely sintered in one stage. The phenomenon in which a single exothermic peak appears in this low temperature range is unique.

  In this DTA analysis, an exothermic peak derived from silver particle sintering appears around 180 ° C., which is higher than the temperature of the low-temperature sintering test (150 ° C.). This difference is due to the difference in heating conditions. In other words, the DTA analysis always changes (increases) the heating temperature, and is an analysis method that captures the sintering behavior based only on thermal factors. Considering the use of the metal paste (wiring material, bonding material, etc.), in actual use, the temperature is maintained at a constant temperature and sintering proceeds with time. In the DTA analysis, the time difference was not reflected in the results, so it can be said that a temperature difference was observed. And the low-temperature sintering test of this embodiment is equivalent to the heating conditions (fixed at 150 ° C. and held for a certain period of time) in actual use. From this test result, the metal paste suitable for this embodiment is It can be understood that the low temperature sintering property is excellent.

  In addition, regarding the cracks observed in the sintered body of the metal paste (ac) mainly composed of fine silver particles having a particle size of 20 to 30 nm, the cause is that the metal paste exhibits a two-stage sintering behavior. It is believed that there is. In this regard, FIG. 5 is an SEM photograph of 180 ° C. and 210 ° C. sintered bodies of pastes c and f. At 180 ° C., which is the first stage, no cracks occurred in the sintered bodies for both pastes c and f. However, at 210 ° C. corresponding to the second stage for c, many cracks are generated only in c. That is, the crack in the paste c is generated during the second stage sintering. It can be said that such a crack does not occur in the paste f not subjected to multi-stage sintering.

  However, in the observation of the entire sintered body, the paste c and the paste f are different from each other in terms of the presence or absence of cracks, but are close to each other microscopically. FIG. 6 is an enlarged view of the photograph of 210 ° C. heating in FIG. According to this photograph, the pastes c and f are very similar in shape and particle size (about 500 nm) of individual particles constituting the sintered body. From this, the hypothesis holds that the diameter of the thermally stable unit particles (units) in the silver sintered body is roughly determined regardless of the particle diameter of the silver particles before sintering. According to this hypothesis, if the silver particles before sintering are composed only of nano-sized fine particles, the amount of movement of the particles is large until it grows into the above stable unit, which tends to cause voids, If the volume of the void exceeds the limit, it is assumed that the units are disconnected from each other and cause cracks.

  In addition to the thermal behavior of the fine silver particles described above, the results of DTA analysis reconfirm that it is necessary to select an appropriate amine as a protective agent for the silver particles. When oleic acid is used as a protective agent instead of an amine compound, the temperature is as high as 200 ° C. or more (metal paste i) although there is only one exothermic peak due to sintering. Moreover, although the silver particle ratio with a particle size of 100-200 nm is suitable for the metal paste g, since the amine compound with a high boiling point was applied, the exothermic peak expressed at 200 degreeC or more. Even when the particle size is too large, the exothermic peak does not appear unless it is 200 ° C. or higher (metal paste m).

As described above, the silver paste according to the present invention acquires low-temperature sinterability by adjusting the particle size range of the main silver particles. The silver sintered body formed according to the present invention has a low resistance and a sufficient bonding strength. It can be widely used as a wiring material, a bonding material or a heat conduction material that requires a sintering process at a low temperature.

Claims (7)

In a metal paste formed by kneading a solid content composed of silver particles and a solvent,
The solid content is composed of silver particles containing 30% or more of silver particles having a particle size of 100 to 200 nm on the basis of the number of particles,
The average particle diameter of the entire silver particles constituting the solid content is 60 to 800 nm,
Furthermore, the silver particles constituting the solid content are bonded with an amine compound having a total carbon number of 4 to 8 as a protective agent ,
A metal paste in which an exothermic peak due to the sintering of silver particles in TG-DTA analysis appears at less than 200 ° C. 2. The metal paste according to claim 1 , wherein a ratio (N / Ag) of a nitrogen concentration (mass%) and a silver particle concentration (mass%) in the metal paste is 0.0003 to 0.003. The amine compound as a protective agent is butylamine, 1,4-diaminobutane, 3-methoxypropylamine, pentylamine, 2,2-dimethylpropylamine, 3-ethoxypropylamine, N, N-dimethyl-1,3- The metal paste according to claim 1, which is diaminopropane, 3-ethoxypropylamine, hexylamine, heptylamine, N, N-diethyl-1,3-diaminopropane, or benzylamine. The metal paste according to any one of claims 1 to 3 , wherein the solvent is an organic solvent having 8 to 16 carbon atoms and an OH group in the structure and having a boiling point of 280 ° C or lower. In the method for producing a metal paste for producing a solid content composed of silver particles and kneading the solid content and a solvent,
The production process of the silver particles is as follows:
(1) A step of mixing a thermally decomposable silver compound and an amine compound to form a reaction system comprising a precursor silver-amine complex and moisture ;
(2) a step of heating the reaction system containing the precursor to a temperature equal to or higher than the decomposition temperature of the silver-amine complex to precipitate silver particles;
The method for producing a metal paste, wherein the water content of the reaction system is 5 to 100 parts by weight with respect to 100 parts by weight of the silver compound before the heating (2). Furthermore, the manufacturing method of the metal paste of Claim 5 including the process of adding the organic compound shown by the following formula which has amide | amido as a skeleton to the reaction system before a heating of (2).
Silver compounds with pyrolytic is silver oxalate, silver nitrate, silver acetate, silver carbonate, silver oxide, silver nitrite, silver benzoate, silver cyanate, silver citrate, claim is any one of silver lactate The manufacturing method of the metal paste of Claim 5 or Claim 6 .