Crystallographic Examination of High Thermal Stability of Dense Sintered Copper Layer

Inhalt:
The higher temperature wide-bandgap (WBG) power devices are operated at, the higher necessity of a Cu sinter paste that can form a bonding layer with high thermal stability is increased. We have newly developed a Cu sinter paste containing highly dispersed submicron Cu particles. It provides a dense Cu bonding layer by pressure sintering under N2. The thermal stability of the Cu bonding layer was evaluated by a thermal cycle test (TCT) between –55 °C and 200 °C under air and a high temperature storage test (HTST) at 250 °C for 1000 h under air. The Cu bonding layer showed no significant change in microstructure and no significant delamination before / after TCT and HTST. Crystallographic evaluation proved that no plastic strain was accumulated in the Cu bonding layer against thermal stress that was generated in TCT and HTST and that the microstructure of the Cu bonding layer was almost kept in the initial state and did not deteriorate like usual Ag sintered layers. Oxidation of the Cu layer did not proceed during the TCT and HTST. Therefore, the dense Cu bonding layer showed high thermal stability from a crystallographic viewpoint.