Impact of Metallurgical and Mechanical Properties of Sintered Silver Joints on Die-Attach Reliability of High-Temperature Power Modules

摘要

Sintered silver bonding processes are expected tooffer bonding solutions with high heat endurance for power modulesusing wide bandgap semiconductors. This study reports the dieattachreliability of the bonding process under thermal cycling tests,focusing on the metallurgical and mechanical properties of sinteredsilver joints. A nanocrystalline (NC) structure with 150-nm-sizedgrains was observed in the as-sintered state, while a coarsenedstructure with microsized grains and pore coalescence was observedafter annealing at 350°C for 1 h. In addition, the increase ofbonding pressure reduced the number of coarse pores. Transmissionelectron microscope observations showed favorable crystallinestructure along the grain boundaries. Tensile tests at roomand high temperature revealed that the sintered silver materialsshowed the inherent mechanical properties of NC metals. Thermalcycling tests of die-attached specimens demonstrated the temperaturedependence of crack resistance at constant amplitude.Furthermore, coalescence of pores and coarsening of grainsreduced bonding reliability. It can be inferred from the resultsthat NC structure and minute pore dispersion improves bondingreliability.