JP6380852B2 - Heat resistant, acid resistant, conductive metal material - Google Patents

Description

  The present invention provides a completely new metal material that has high temperature heat resistance, acid resistance, and electrical conductivity, and that forms a metal after molding rather than molding a conventional metal.

Conductive bonding agents and pastes are used in the heart of electronic circuits, and are mainly used as materials for connecting semiconductors and functional parts to substrates and printed wiring.
Conventionally, so-called silver paste has been used for a long time as this paste agent, but it has many problems in the stability of the preparation, the conductivity after joining, the durability, the heat resistance and the like. In particular, when silver paste is used for printed wiring, elution due to the weak acid resistance of silver occurs, and so-called migration that short-circuits the wiring becomes a big problem.
On the other hand, recently, many electronic / electrical members such as power modules are often partially exposed to high heat of 600 ° C. or more, and heat resistance in this high temperature region is required. However, the heat-resistant temperature of conventional processing materials centering on solder has not reached 300 ° C. at the maximum.

For this reason, it is necessary to rely on so-called brazing, and a process of brazing after securing the heat resistance of 1000 ° C. or higher by isolating the processed part from other parts is unavoidable. However, no matter how tightly the enclosure is, heat leaks around the heated portion, and as a result, residual strain is unavoidable in the member.

As means for solving these problems, for example, as disclosed in Japanese Patent No. 5442666 (Patent Document 1) and the like, a conductive material that is sintered and solidified in a newly melted solder of metal nanoparticles. Bonding agents have been proposed.

However, this technology is theoretically an epoch-making technology, and the molten solder functions well as a binder for nanoparticles, and when taken out after sintering, it forms a complete mass, and adhesion There is also conductivity. However, since the solder content remains in the form of the ridge, when reheated, the solder portion melts and becomes a break point, and the whole becomes disjoint. In other words, the finished sintered body does not have heat resistance higher than the melting point of the solder used.

Japanese Patent No. 544266

The present invention is to examine the above-mentioned prior art technology in detail and add further improvements.

The results of scrutinizing the performance of the finished sintered body by varying the composition ratio in the bonding agent combining silver nanoparticles and bismuth / tin solder, which is an example of the above prior art. It was found that there was a singular point in the composition ratio.
That is, metallic luster was developed only when a specific composition ratio was used, and all of the sintered bodies had heat resistance of 1000 ° C. or higher.
In other words, the basic technical configuration of the present invention includes metal nanoparticles having low temperature sinterability coated with a coating material designed in advance to peel at a predetermined temperature, and solder having a melting point lower than the peeling temperature. Of the metal material composed of three components of powder and a pasting agent that evaporates at a temperature higher than the melting point and lower than the peeling temperature, the metal nanoparticles are silver nanoparticles, and the solder powder is tin-bismuth. The solder ratio of the two, and the mixing ratio of the two is such that the amount of the nano silver component relative to the tin solder component 1 is 0.91 sn / a (where s = the content of tin in the tin solder is wt%, a = a pure content of silver in silver nanoparticles wt%, n = 1 or an integer of 1 or 4 ), a heat-resistant / acid-resistant / conductive metal material.

  In the present invention, by adopting the above-described technical configuration, conventional defects are improved, high temperature heat resistance, acid resistance, and conductivity are obtained. For the first time, it became possible to produce completely new metal materials.

That is, as a result of analyzing this sintered body with fluorescent X-rays, all are intermetallic compounds having a structure of Bi.Sn/NAg (N = 1 to 4), and from the DTA measurement results, It had a heat resistance of 1000 ° C. or higher.
That is, when silver nanoparticles are sintered, it is presumed that they react with tin in the solder to form an intermetallic compound. However, at the same time, it was also found that heat resistance does not appear at all at composition ratios other than singularities.

In order to improve acid resistance, which is the biggest drawback of silver, mixing tin with silver has long been done, and in fact, complete intermetallic compounds are used as dental treatment materials.
However, the intermetallic compound of tin and silver has a structure in which three silver atoms are attached to the tin atom, and its energy level is extremely low compared to the others. All the intermetallic compounds inside have this structure.
For example, when a small amount of tin is mixed with silver for the purpose of only improving the acid resistance of silver, only this trimeric intermetallic compound is separated from the silver, and the interlaminar layer becomes a break point. The whole becomes fragile. Therefore, in practice, measures are taken to avoid intermetallic compounds as much as possible by mixing the third component.

On the other hand, in the case of the present invention, the reaction between silver and tin occurs instantaneously in a very limited space and solidifies. Therefore, the rearrangement of atoms by so-called reflow and reaction points propagate to other spaces. It is possible to adopt all metastable structures that have no room for energy levels.
Therefore, a high-purity intermetallic compound can be formed only in the case of a limited stoichiometrically calculated blending ratio, and in other blending compositions, unreacted solder particles remain dispersed, and the portion When the sintered body is reheated at, for example, 150 ° C., it breaks apart and completely loses heat resistance and adhesiveness.

Furthermore, a feature of the metal material of the present invention is that the pasted material is made into a metal by a simple heat treatment.
That is, dry silver plating can be performed by applying a paste after applying a paste to the substrate surface using a brush or the like, and so-called printed wiring can be obtained by drawing a line on the substrate by a method such as screen printing. In addition, it is conceivable to use it as a material for 3D printers as a lump processing case, and to make decorative tools and machine parts. In addition, an interesting example of this case is a new one that can be molded in the clinic. Development as a dental treatment tool can be mentioned.
Of course, it can be applied to a new bonding agent instead of solder or silver paste.
In particular, it has been considered impossible to join in the past if we take advantage of the characteristics of nanoparticles that enter into small irregularities on the surface of the substrate and solidify it to realize strong bonding with the substrate. Bonding to substrates of all materials such as aluminum and stainless steel is possible.

Details of the heat-resistant / acid-resistant / conductive metal material of the present invention will be described below.
That is, the basic technical idea of the heat-resistant / acid-resistant / conductive metal material according to the present invention includes low-temperature sinterable metal nanoparticles coated with a coating material designed in advance to be peeled off at a predetermined temperature. Among the metal materials composed of three components of solder powder having a melting point lower than the peeling temperature and a pasting agent that evaporates at a temperature higher than the melting point and lower than the peeling temperature, the metal nanoparticles are silver nanoparticles. The solder powder is a tin-bismuth solder powder, and the mixing ratio of the two is such that the amount of the nano silver component relative to the tin solder component 1 is 0.91 sn / a (where s = tin Heat resistance / acid resistance, characterized by satisfying the following relationship: tin content in solder based on wt%, a = pure silver wt% in silver nanoparticles, n = 1 or an integer of 4 It is a conductive metal material.

By the way, in the present invention, the metal nanoparticles having low-temperature sinterability refer to so-called single nanoparticles having a particle diameter of 10 nm or less. In addition, in the present invention, it is necessary to further cause a metal reaction in the sintering process. Generally, the smaller the particle size, the higher the reaction activity, and therefore the particle size of the nanoparticles is preferably 5 nm or less. However, to date, only gold nanoparticles and silver nanoparticles have existed alone with a particle size of 5 nm or less. Furthermore, silver nanoparticles are actually commercially available as nanoparticles. There are only particles.
Although there are several reports on the impact of single nanometal particles on human health, no final conclusion has been reached. Therefore, although the Ministry of Health, Labor and Welfare is instructing the government to “wet particles to prevent inhalation exposure to workers due to volatilization”, there is no specific instruction on the degree of wetting and the method of wetting.

On the other hand, as a tin solder, the temperature range in which the temperature can be controlled with a simple control system using a heat source having high versatility in the heat treatment process of the present invention is between 150 ° C. and 200 ° C. It has been broken. There are not many low-temperature solders having a melting point in the vicinity and generally spread, and it is desirable to use bismuth / tin solder having a melting point in the range of 135 ° C. to 145 ° C.

The mixing ratio of silver nanoparticles and solder powder forms the basis of this technology and is extremely important. In other words, when silver nanoparticles are dispersed in a molten solder and sintered, the properties of the silver nanoparticles as atoms and the heat generated by the binding energy generated during sintering at low temperatures contribute to the reaction heat. By doing so, an intermetallic compound is formed with the tin in the solder.
Therefore, stoichiometrically calculated 0.91 sn / a: 1 (where s = wt% tin content in tin-based solder, a = pure silver wt% in silver nanoparticles, n = An integer of 1 to 4) only in the case of a compounding ratio, a highly pure intermetallic compound having high heat resistance is obtained, but in other compounding compositions, unreacted solder particles remain dispersed, When the portion becomes a break point, for example, when the sintered body is reheated at 150 ° C., it disintegrates and heat resistance and adhesiveness are completely lost.

As a result of repeating a number of experiments and considerations regarding the mixing ratios for the respective compositions described above, the present inventor has found that the mixing ratio of the weight of silver nanoparticles to the solder powder is determined by the ratio of silver nanoparticles to tin in the solder. It has been found that they are extremely strongly related to their respective molar mass ratios, and many experiments and discussions are repeated, and the necessary conditions from the viewpoint of economics when industrialized are taken into account. As a result, it was found that the molar mass ratio between the silver nanoparticles and tin in the solder can be 1 to 4, and the ratio of the amount of each of the silver nanoparticles and solder powder used is It has been found that the object of the present invention is realized by setting the values shown in the respective weight percentages shown below.
That is,
Mixing ratio of silver nanoparticles = (0.91 sn / a) / ((0.91 sn / a) +1)
And also
Solder powder mixing ratio = 1 / ((0.91 sn / a) +1)
Where s = content of tin in solder powder wt%, a = silver pure content in silver nanoparticles wt%
n is an integer of 1 to 4.

Hereinafter, specific examples showing an example of a method for producing the heat-resistant / acid-resistant / conductive metal material in the present invention will be described in the form of examples, but the present invention is specified within the description range of the following examples. It goes without saying that it is not a thing.
Example 1
(When n = 4)
70.1: Silver nanoparticles having a mean particle diameter of 5 nm (pure silver content: 65 wt%) and bismuth / tin solder powder (melting point: 145 ° C., tin content: 41.8 wt%) coated with a higher alcohol peeled at 185 ° C. Mix at a mixing ratio (weight basis) of 29.9 and paste into terpene oil that evaporates around 140 ° C. to make a conductive bonding agent. A bonding agent is dropped on a glass plate and heat-treated in an infrared oven heated to 150 ° C. for 10 minutes, then heated to 200 ° C. and further heat-treated for 10 minutes.
(Result of Example)
As a result of analyzing the sintered body by X-ray fluorescence, an intermetallic compound of Bi · Sn / 4Ag was present. Furthermore, the DTA measurement result showed a heat resistance of 1000 ° C. or higher.

Example 2
(When n = 4 and the solder component is slightly increased)
Silver nanoparticles having an average particle diameter of 5 nm (pure silver content: 65 wt%) coated with higher alcohol that is peeled off at 185 ° C. are mixed with bismuth-tin solder powder (melting point: 145 ° C., tin content: 41.8 wt%) at 65.0%. : Mix in a mixing ratio (weight basis) of 35.0, and paste into terpene oil that evaporates around 140 ° C. to make a conductive bonding agent. A bonding agent is dropped on a glass plate and heat-treated in an infrared oven heated to 150 ° C. for 10 minutes, then heated to 200 ° C. and further heat-treated for 10 minutes.
(Result of Example)
As a result of analyzing the sintered body by X-ray fluorescence, a Bi.Sn/4Ag intermetallic compound and a Bi.Sn alloy coexisted. Further, in the DTA measurement result, an endothermic peak was present at 145 ° C., and this part became a break point, and it was found that the whole collapsed at this temperature.

Example 3
(When n = 1)
Silver nanoparticles with a mean particle size of 5 nm (pure silver content 65 wt%) coated with a higher alcohol that is peeled off at 185 ° C., 36.9% of bismuth-tin solder powder (melting point 145 ° C., tin content 41.8 wt%) : Mix in 63.1 mixing ratio (weight basis), and paste into terpene oil that evaporates around 140 ° C. to make a conductive bonding agent. A bonding agent is dropped on a glass plate and heat-treated in an infrared oven heated to 150 ° C. for 10 minutes, then heated to 200 ° C. and further heat-treated for 10 minutes.
(Result of Example)
As a result of analyzing the sintered body by fluorescent X-ray, an intermetallic compound of Bi · Sn / Ag was present. Furthermore, the DTA measurement result showed a heat resistance of 1000 ° C. or higher.

Example 4
(When n = 1 and the amount of solder is slightly increased)
Silver nanoparticles having an average particle diameter of 5 nm (pure silver content: 65 wt%) coated with a higher alcohol that is peeled off at 185 ° C. are mixed with 30.0% bismuth-tin solder powder (melting point: 145 ° C., tin content: 41.8 wt%). : Mix at a mixing ratio (weight basis) of 70.0, and paste into terpin oil that evaporates around 140 ° C. to make a conductive bonding agent. A bonding agent is dropped on a glass plate and heat-treated in an infrared oven heated to 150 ° C. for 10 minutes, then heated to 200 ° C. and further heat-treated for 10 minutes.
(Result of Example)
As a result of analyzing the sintered body by fluorescent X-ray, a Bi · Sn / Ag intermetallic compound and a Bi · Sn alloy coexisted. Further, in the DTA measurement result, an endothermic peak was present at 145 ° C., and this part became a break point, and it was found that the whole collapsed at this temperature.

Claims (1)

Metal nanoparticles having low temperature sinterability coated with a coating material designed in advance to peel at a predetermined temperature, solder powder having a melting point lower than the peeling temperature, and above the melting point and above the peeling temperature Among the metal materials composed of the three components of the pasting agent that volatilizes at a low temperature, the metal nanoparticles are silver nanoparticles, the solder powder is a tin-bismuth solder powder, and a mixture of the two The ratio is that the amount of the nanosilver component relative to the tin-based solder component 1 is 0.91 sn / a (where s = the tin content in the tin-based solder wt%, a = the pure silver content in the silver nanoparticles) wt%, n = 1 or an integer of 1 or 4 ), a heat-resistant / acid-resistant / conductive metal material.