January 28, 2020

Notice Regarding Development of Bonding Sheets
Using Copper Nanoparticles for Power Device Applications
Taiyo Nippon Sanso Corporation (“TNSC”) hereby announces that it has successfully developed
bonding sheets using highly sophisticated and reliable copper nanoparticles for next-generation powerdevices such as silicon carbide (SiC) and gallium nitride (GaN).

1. Background
Power devices are semiconductor chips used in power conversion equipment such as inverters andconverters for electric and hybrid vehicles. To make power devices highly efficient requires module
miniaturization and raising the limit of their working temperature to increase the density of power
output.
However, conventional mainstream silicon (Si) power devices have an operating temperature of150°C, limiting the extent of module miniaturization due to heat resistance problems.
Device materials such as SiC and GaN are capable of operating at temperatures of 200°C or above,raising expectations of them becoming an alternative to Si power devices. Now, solder materials areoften used as bonding materials for conventional Si power devices in electronic components, but these
are lacking in heat resistivity and not suitable with SiC power devices projected for use in high temperature environments, which boosted a need for bonding materials capable of high-temperature
operations.
Metallic nanoparticles are attracting attention as a possible alternative for existing bonding
materials used in power devices such as SiC, and they have raised expectations in particular from thestandpoint of their ion migration * resistance and production cost. Generally, metallic nanoparticle
welding materials are used as a paste but need to undergo a predrying process to eliminate solvents,
requiring thermic pyrolysis to remove binders when sintering nanoparticles, with the risk of generating
decomposed gas that can form voids or cracks in the bonding layer. There was an issue of maintaining
powerful binding strength and ensuring reliability.

- 1 -2. Overview of bonding sheets using copper nanoparticles
TNSC can use its oxygen combustion technology to fire particles under a reduction atmospherewith low-temperature firing at 150°C through a process using one of its technologies that dries copper
particles covered in a suboxide layer with a particle size of about 100 nm and surface of several nmthat enables them to be produced in large volumes.
TNSC has successfully developed bonding sheets capable of bonding without predrying under anitrogen atmosphere (Fig. 1) or adding a reducing gas such as hydrogen, yet with high binding strengthand outstanding reliability (Photo 1). It has done this by using copper nanoparticles synthesized to bebinderless in a the production process, adding a small volume of reducing agent and optimizing thebonding layer structure.
A sample bonding SiC and a copper plate using this bonding material was confirmed to ensure highreliability at over 1,000 cycles in a heat cycle test without any interface peeling seen.

Photo 1: Copper nanoparticle bonding sheet

Fig. 1: Correlation between bonding pressure andshearing strength for a bond at 300°C for 5
minutes

3. Future plans
Going forward, TNSC will promote this bonding material for users and move ahead on user
developments.
TNSC will give a verbal briefing of its findings at the 26th Symposium on Micro binding andAssembly Technology in Electronics (Mate 2020) (Venue A, Program No. 19) held at Pacifico
Yokohama on Wednesday, January 29, 2020.
In addition, TNSC will also set up a booth (3W-N0O9) at the neo functional material 2020
exhibition held at Tokyo Big Sight from Wednesday, January 29 to Friday, January 31, 2020.

* Ion migration: A state where metals between electrodes are ionized and cause short circuits when voltage is applied inhumid environments- 2 -