Journal of Materials Science, Vol.56, No.16, 9852-9870, 2021
Fracture mechanism of microporous Ag-sintered joint in a GaN power device with Ti/Ag and Ni/Ti/Ag metallization layer at different thermo-mechanical stresses
Ag sinter joining technology is emerging as a die attach material for next-generation power modules in high-temperature applications. Thermal shock test has revealed that the fracture characteristics and reliability of sintered Ag joint were influenced by thermo-mechanical stress. This was study conducted to understand the microstructure, vertical crack formation, and fracture behavior of sintered Ag joints which were designed with different metallization layers on a direct bonded aluminum (DBA) substrate, at different thermo-mechanical stresses during thermal shock tests. Two kinds of metallization layers were designed as Ti/Ag and Ni/Ti/Ag layers. A finite element model (FEM) simulation confirmed that the Ni layer prohibited Al hillock-like deformation and generates different thermo-mechanical stresses during the thermal shock test from - 50 degrees C to 250 degrees C. Depending on the degradation of the interfaces for both of the Ag-sintered joints, the sintered Ag grain necking thickness and microstructure characteristics including the Ag grain structures, which have a dominant influence on the bonding strength in terms of long-term reliability, are considerably different from the results by an electron back scatter diffraction (EBSD) analysis. This paper proposes a novel metallization technology that can induce joint fracture with complete recrystallization of sintered Ag joints by effectively suppressing interfacial degradation. The mechanism of this technology was systematically analyzed through experiments and FEM simulations.