Thermal Shock Performance of DBA/AMB Substrates Plated by Ni and Ni⁻P Layers for High-Temperature Applications of Power Device Modules

The thermal cycling life of direct bonded aluminum (DBA) and active metal brazing (AMB) substrates with two types of plating-Ni electroplating and Ni⁻P electroless plating-was evaluated by thermal shock tests between -50 and 250 °C. AMB substrates with Al₂O₃ and AlN fractured only after 10 cycles, but with Si₃N₄ ceramic, they retained good thermal stability even beyond 1000 cycles, regardless of the metallization type. The Ni layer on the surviving AMB substrates with Si₃N₄ was not damaged, while a crack occurred in the Ni⁻P layer. For DBA substrates, fracture did not occur up to 1000 cycles for all kind of ceramics. On the other hand, the Ni⁻P layer was roughened and cracked according to the severe deformation of the aluminum layer, while the Ni layer was not damaged after thermal shock tests. In addition, the deformation mechanism of an Al plate on a ceramic substrate was investigated both by microstructural observation and finite element method (FEM) simulation, which confirmed that grain boundary sliding was a key factor in the severe deformation of the Al layer that resulted in the cracking of the Ni⁻P layer. The fracture suppression in the Ni layer on DBA/AMB substrates can be attributed to its ductility and higher strength compared with those of Ni⁻P plating.