Effects of Large-Temperature Cycling Range on Direct Bond Aluminum Substrate

Substrate reliability has, for a long time, been a concern for systems exposed to harsh environments. State-of-the-art direct bond copper (DBC) substrate is susceptible to large-temperature cycling range. Due to the coefficient of thermal expansion mismatch between copper and the base ceramic (e.g., Al₂O₃ and AlN), delamination of copper from the ceramic base plate caused by thermomechanical stresses is often observed. In this paper, effects of large-temperature cycling range on direct bond aluminum (DBA) substrate reliability were investigated as it could be a viable alternative to DBC. DBA substrates with different metallizations were thermally cycled between -55degC and 250degC. Unlike the DBC substrate, no delamination of aluminum from the aluminum-nitride ceramic base plate was observed in the DBA substrates. However, it was observed that surface roughness of metallization increased during the thermal cycling test. It is believed that, in the high-temperature regime, the significant amount of thermal stress and grain-scale deformation caused recrystallization and grain-boundary sliding to become very active in the aluminum layer, thus leading to the observed increase in surface roughness. The influence of metallization over the aluminum surface on the extent of surface roughness was also characterized.