TANAKA Kikinzoku Kogyo K.K., which is a TANAKA Precious Metals company that operates a manufacturing business, developed Active Brazing Filler Metal/Copper Composite Material for power devices in 2021. This product is made by cladding an active brazing filler metal on one side of a copper material. The product can be used to join various materials, including ceramic (oxides, nitrides, and carbides) and carbon materials, and it helps to reduce silver bullion and process costs. Because of its versatility and usability, this product has wide-ranging potential, including reducing development lead times when applied to heat dissipation of power devices used, for example, for EVs and contributing to the development of next-generation heat sinks. This product is the result of the creativity and imagination harnessed in TANAKA Kikinzoku’s research and development. In this interview, Takaomi Kishimoto and Shinichiro Kitaoka, who in the development of the Active Brazing Filler Metal/Copper Composite Material were in charge of engineering and sales, respectively, talk about their “two breakthroughs.”

The new Active Brazing Filler Metal was born in an environment in which we could keep trying new things

Brazing is a way of joining two metals. “Brazing filler metals,” which serve as glue for joining base metals, when melted, penetrate into 50-to-200-micrometer gaps between the base metals by capillary action to join the metals.

The great advantage of the Active Brazing Filler Metal/Copper Composite Material, which TANAKA Kikinzoku Kogyo K.K. developed for power devices, is that it can be used to directly join ceramics, which cannot be done with conventional brazing filler metals. This achievement is possible because of the material’s unique brazing filler metal, which is made by adding titanium to a conventional brazing filler metal. This product was developed through trial and error.

Kishimoto: “Active brazing filler metals have been used for a long time. About 10 years ago, silver-copper-titanium alloy was more commonly used as a brazing filler metal. However, brazing filler metal made of silver-copper-titanium alloy had a problem in that large, hard copper-titanium particles of over 100 micrometers formed in the alloy.”

▲ Takaomi Kishimoto, Chief Engineer, Manufacturing Engineering Section, Tomioka Plant, AuAg Company, TANAKA Kikinzoku Kogyo K.K.

A brazing filler metal containing hard copper-titanium particles is like clay containing small stones. Imagine spreading such clay thinly. Small stones come to the surface, forming a bumpy surface. In brazing, a brazing filler metal is spread thinly to form a film. However, if the brazing filler metal contains hard copper-titanium particles, voids are formed in the brazing filler metal film, which causes problems with brazing.

Kishimoto: “We proceeded by trial and error, thinking it might be possible to prevent the formation of large copper-titanium particles by adding an additive to silver-copper-titanium alloy. We studied which additive to use and found that adding tin could disperse the copper-titanium particles into smaller particles.”

The additive was found through trial and error as stated.

Kitaoka: “What is important is how much tin to add. Through repeated trial and error, we found that it is ineffective to add a small amount of tin; it is important to add at least a certain amount. We found the most appropriate amount of tin to add that allows for fine dispersion of texture, and this led to significant progress in the development of active brazing filler metals. This enabled stable film formation of brazing filler metal, which was the first breakthrough.”

▲ Shinichiro Kitaoka, Leader, Sales Department 2, AuAg Company, TANAKA Kikinzoku Kogyo K.K.

This breakthrough was achieved thanks to TANAKA Kikinzoku’s research and development system in which researchers are encouraged to try things as many times as they like.

Kishimoto: “In research and development using precious metals, it is generally difficult to conduct experiments because precious metals are expensive. However, TANAKA Kikinzoku can use many bullions to prepare and evaluate various samples during this stage because we have well-developed internal systems for recovering, refining, and recycling bullions. Even if an experiment is unsuccessful, the precious metals used can be recycled with our internal recovery and refinery processes, which allows us to readily try out ideas. As a result, TANAKA Kikinzoku has a culture in which we are encouraged to prepare and evaluate samples without hesitation, which is what brought about this breakthrough.”

This new product was created to meet customer needs

Kitaoka: “Using TANAKA Kikinzoku’s technologies for cladding, we successfully produced this product with a high degree of perfection, which was the second breakthrough.”

The Active Brazing Filler Metal/Copper Composite Material for power devices is made by cladding an active brazing filler metal on one side of a copper material. TANAKA Kikinzoku could realize such manufacturing because it cares greatly about customer needs.

Kitaoka: “The Active Brazing Filler Metal/Copper Composite Material for power devices was not born through the course of our product development but rather by knowing customer needs. Our job is to listen to customers to learn of their problems and challenges and then to solve such issues. One day, I was talking with someone from a major electrical appliance manufacturer and found that they had a challenge with ceramic circuit substrates (AMB (Active Metal Brazed) substrates). To increase the heat dissipation of a ceramic circuit substrate, the thickness of the copper sheet to be joined must be increased. However, it was difficult to form a thick copper electrode on ceramics by the conventional means of etching (chemical corrosion). So, as a technology to form a thick copper electrode and produce a ceramic circuit substrate without etching, we focused on the aforementioned active metal using silver-copper-tin-titanium alloy and our Iwate Plant’s advanced cladding technology. We prepared samples by combining these two technologies for the customer’s evaluation, which was very positive. This is the starting point of the development of the Active Brazing Filler Metal/Copper Composite Material for power devices as a product for ceramic circuit substrates.”

He said that such a breakthrough is born at the intersection between creativity and imagination.

Kitaoka: “Basically, all of the products we offer are customized to individual customers. In other words, our job lies at the intersection between creativity and imagination. First comes creativity, which we use to conduct research and development to solve the customer’s challenge. Then comes imagination, with which the customer uses what we have created and predicts what will happen during use through trial and error. Together with our customers, we offer good things in a good way through a cycle of creativity and imagination. This product was born out of this cycle.”

With the Active Brazing Filler Metal/Copper Composite Material for power devices, because a brazing filler metal is already cladded on a copper material, ceramic circuit substrates can easily be manufactured merely by setting the material on the ceramics and brazing it. This eliminates the need for etching, which helps reduce process costs.

▲ Active Brazing Filler Metal/Copper Composite Material (center and right) and joining example (left)

Precious metals have good chemistry with the recycling society

TANAKA Kikinzoku group’s manufacturing is supported by its meticulous precious metals recycling environment, which will also be important to support the recycling society.

Kitaoka: “I repeat myself, but TANAKA Kikinzoku has a well-established internal environment for recycling precious metals. For example, the metals contained in mill ends from manufacturing processes and materials used in research and development are swiftly recovered and refined into pure gold and silver, which are then re-used as raw materials. I believe that our environment in which we can do such recycling in a one-stop fashion not only gives us an advantage in product development but also enables our customers to contribute to society.”

The Active Brazing Filler Metal/Copper Composite Material for power devices has great potential in the EV market, which is expected to grow exponentially. Moreover, the product will contribute to energy conservation and efficiency improvement in power devices, thereby helping to preserve the global environment.

Kitaoka: “We hope to join various materials using joining materials, thereby creating innovations that cannot be achieved with a single material. Thus far, metallic heat sinks have generally been used for heat dissipation. Today, however, many materials that dissipate more heat than metals have been developed. Active brazing filler metals can be applied in the process in which such a new material is joined to another material to realize an innovation.”

Kishimoto: “TANAKA Kikinzoku can achieve such innovations from its development and manufacturing sites, where we have already established a recycling system. Precious metals have good chemistry with the recycling society. For example, it is difficult to recycle products made of organic materials into raw materials, but it is possible to recycle products made of precious metals into raw materials. I believe that it is possible to realize a society in which all bullions used in products, including gold and silver, can be recycled. Currently, almost all bullions used within TANAKA Kikinzoku are recycled, not disposed of. It would be great if bullions could be recycled throughout all of society.”

TANAKA Kikinzoku will bring innovations to society with precious metals, which are gifts from the earth, thereby contributing to global environment preservation.

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