Improvement of High-temperature Reliability of Power Modules by Multi-step Temperature Bonding Process of Zn-Al Solder

Conference: CIPS 2020 - 11th International Conference on Integrated Power Electronics Systems
03/24/2020 - 03/26/2020 at Berlin, Deutschland

Proceedings: ETG-Fb. 161: CIPS 2020

Pages: 6Language: englishTyp: PDF

Hozoji, Hiroshi; Kato, Fumiki; Sato, Shinji; Sato, Hiroshi; Yamaguchi, Hiroshi (Advanced Power Electronics Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Center 2, 1-1-1, Umezono, Tsukuba, Ibaraki, 305-8568, Japan)

In this paper, we describe the bonding process and bonding stability of Zn-Al solder and the reliability results of temperature cycle tests. XPS analysis showed the presence of oxides that could not be reduced by formic acid on the surface of Zn-Al solder. The reliability test results of power modules assembled using Zn-Al solder were unstable because of it was difficult to form good joints with Zn-Al solder oxides. We have found that diffusion proceeds at the interface by holding the Zn-Al solder and copper in contact at a temperature below the melting point. By adding a process using this diffusion, the bonding state of Zn-Al solder has been improved. This solder joining process was applied to the assembly process of the SiC 2-in-1 power module. This module showed no increase in thermal resistance due to the significant degradation of the bonding layer in transient thermal analysis after 1000 cycles of -40deg C / 250deg C temperature cycling.