Bonding interface materials evolution of intermediate In/Ag layers for low temperature fluxless solder based MEMS wafer level packaging

In this paper, we proposed new intermediate bonding layers (IBLs) of Ag-rich composition in In-Ag solder systems in contrast to previous studies mainly based on eutectic composition. The intermetallic compounds (IMCs) at the bonding interface were investigated with respect to the bonding condition, post-bonding room temperature storage and post-bonding heat treatment. The IMCs of Ag
₂
In and Ag
₉
In
₄
with high temperature resist to post-bonding process are derived under process condition of wafer bonding at 180degC, 40 mins and subsequent 120degC~130degC annealing for 24 hours. Based on our results, we can design proper packaging process flow so as to get reliable wafer level packaged MEMS devices.