Thermal shock reliability of GaN die-attached on DBA with Ag sinter paste

The reliability of GaN / DBA die-attached joint structure with hybrid Ag paste die-attach layer was evaluated in harsh thermal shock. For the joint structure, DBA and GaN chips metallized by Ti/Ag were firstly prepared. GaN die and DBA substrate was bonded at 250 °C without pressure in air sintering condition. The thermal cycles up to 1000 in a temperature range of -50 °C to 250 °C` were implemented for the joint structure. The initial average die shear strength of the GaN/DBA joint structure was about 33 MPa, but reduced after 500 cycles and further significantly reduced below 10 MPa after 1000 cycles. The microstructure was observed by FE-SEM with EDX. Different with Cu layer on the DBC substrate, Al is difficult to be oxidized during the thermal cycling. The decrease of shear strength was mainly attributed by the deformation of Al layer which leading to crack growth in the Ag sinter layer. In addition, this study also further discussed the effect of thermal shock on the microstructure of DBA substrate and Ag sinter paste during the thermal cycling.