Heel crack propagation mechanism of cold-rolled Cu/Al clad ribbon bonding in harsh environment

Abstract

A cold-rolled Cu/Al clad ribbon was bonded on an electroless nickel immersion gold (ENIG)-finished Cu substrate by ultrasonic bonding. The bonding samples were subjected to harsh conditions such as thermal exposure at 200°C and thermal shock at -40/250°C. The microstructural evolution and textural transitions in the Cu/Al clad ribbons were analyzed using electron backscatter diffraction to understand the heel crack propagation mechanism. The heel cracks were initiated at the edge of the Al layer between the bonded and non-bonded zones and were propagated along the coarsened grain boundaries deep into the cladded Cu layer. The continuous dynamic recrystallization (CDRX) transition phenomena around the heel cracks were scrutinized by electron backscatter pattern analysis to reveal the different microstructural and textural evolutions as a function of the ultrasonic bonding process at the bonded part and of lift-up at the non-bonded part. The heel cracks were occurred by grain coarsening due to CDRX within the Al layer during the environmental tests. The region of coarsened grains by CDRX was extended with increasing test periods. Especially in the thermal shock tests at -40/250°C, severe grain coarsening was found involving significant transformation of sub-grains into grains by rapid CDRX development. Thus, heel crack propagation accelerated more during thermal shock cycles than during high-temperature storage.

Measurement of Heat Dissipation and Thermal-Stability of Power Modules on DBC Substrates with Various Ceramics by SiC Micro-Heater Chip System and Ag Sinter Joining

“…Therefore, there have been some issues, for instance how to interconnect these multi-layers to implement in high temperature and have a thermal-stable reliability. In addition, power electronic substrate plays an important role in dissipating heat to prevent power electronic module failure [12,13,14,15,16,17,18]. Heat dissipation/insulation substrate, which is a direct bonded copper (DBC) and a direct bonded aluminum (DBA), are existed between power semiconductor device and heat sink.…”