Silver stress migration bonding driven by thermomechanical stress with various substrates

In recent years, the requirement for environmentally friendly power electronics such as light-emitting diodes and integrated power modules has led to substantial efforts in electronic packaging. The high operating temperatures of advanced power devices particularly require alternative bonding materials to replace the high-temperature solders that contain much Pb. Without limiting the conventional soldering processes that use melting alloys, several candidate materials have been developed, along with the development of devices. In this study, we demonstrate Ag stress migration bonding with various substrate materials to address the intrinsic mechanisms underlying the bonding process. Varying the substrate material changes the thermal expansion mismatch between the sputtered Ag films and the substrate, resulting in different bonding properties, in particular the die shear strength. It has been revealed that a low bonding temperature process can be achieved with a high thermal stress, suggesting that stress migration and resulting stress relaxation at the bonding temperature play key roles in controlling the Ag stress migration bonding. This Ag stress migration bonding opens up a novel opportunity to access wide band-gap devices by realizing low-temperature processes without any application of pressure.