Metals and Materials International | 2019
Thermal Ageing Studies of Sintered Micron-Silver (Ag) Joint as a Lead-Free Bonding Material
Abstract
The sintered silver (Ag) joint has proven to be a suitable die-attach material to be used under the operating conditions of wide bandgap semiconductors because of its high melting point and high thermal and electrical conductivities. However, to bond reliably, a sintered Ag joint needs a suitable metallized substrate (e.g. gold or silver) and the application of pressure during sintering. Hence, we investigated the evolving microstructure (i.e. the importance of pore shape factor) and shear strength of micron-Ag joints bonded without pressure on copper, Ag-plated substrate, and direct-bond copper (DBC) thermally aged at 300 °C for 1000 h. The DBC substrate maintained die-shear strength better because its coefficient of thermal expansion matched those of the sintered Ag and Si dies. Regardless of substrate, micron-Ag joints showed a decrease of large pores (>\u20090.16 µm2) and an increase of spherical pore shapes during the aging period. These favourable changes maintained the mechanical integrity of the micron-Ag joints. This evolving microstructure of the sintered Ag joint provides guidelines for packaging engineers to consider as part of their selection of metallizations and substrates for power electronic packaging.