A Short Time and Ni-sinterable Cu Sinter Paste with Highly Dispersed Submicron Cu Particles

Cu bonding layer with high thermal stability is essential for wide-bandgap (WBG) power devices operated at temperatures of higher than 200°C since it is generally known that Ag bonding layer thermally deteriorates in the microstructure. We developed a novel Cu sinter paste containing highly dispersed submicron Cu particles. It provided a dense bonding layer with high thermal stability despite of mild sintering conditions of a short sintering time and an N2 atmosphere. The thermal stability of the Cu bonding layer was evaluated by a thermal cycle test (TCT) under air. The Cu bonding layer had no significant delamination after the TCT. It shows that the Cu sintered layer endured thermal stress generated at the interface between Si die and the bonding layer. The microstructure of the bonding layers and the crystal orientation of the microstructure were almost the same after the TCT, suggesting that no plastic strain was accumulated in the Cu microstructure. Furthermore, oxidation of the Cu bonding layer did not proceed after TCT under the air. Therefore, it was found that the Cu sinter paste gave a thermally stable Cu bonding layer despite of sintering conditions of an N2 atmosphere for a short time (shorter than 100 s).