Strengthening of DBA substrate with Ni/Ti/Ag metallization for thermal fatigue-resistant Ag sinter joining in GaN power modules

This study was carried out to develop a DBA (direct bonded aluminum) substrate with Ni/Ti/Ag metallization to achieve highly functional thermal shock stability of Ag sinter joining in GaN (Gallium Nitride) power modules. GaN /DBA die-attached module structures by Ag sinter joining was performed during harsh thermal shock cycling tests within a temperature range of − 50/250 °C. In the case of DBA without a Ni metallization layer (Ti/Ag), severe degradation occurred at the interface between the sintered Ag and Al due to significant plastic deformation of the Al layer. The shear strength decreased from an initial value of 33.1 MPa to 22.3 MPa after 500 cycles. With EBSD investigation, it was determined that the Al layer underwent sub-grain rotation recrystallization during thermal shock cycles. This led to a non-uniform grain orientation distribution at center and corner locations. On the other hand, Ni/Ti/Ag metallization showed that it can prevent severe Al deformation due to the superior rigidity achieved by Ni metallization. The die-shear strength maintained almost the same value as its initial value, even after 500 cycles. In addition, a numerical simulation analysis determined that the Ag sinter joining structure on the DBA substrate with Ni/Ti/Ag metallization had high functionality in stress relaxation. This study provided a novel approach to design thermal shock stability Ag sinter joining for next-generation power modules in high-temperature applications.