Study of Ag-In solder as low temperature wafer bonding intermediate layer

Abstract

Indium-silver as solder materials for low temperature bonding had been introduced earlier. In theory the final bonding interface composition is determined by the overall materials composition. Wafer bonding based multiple intermediate layers facilitates precise control of the formed alloy composition and the joint thickness. Thus the bonding temperature and post-bonding re-melting temperature could be easily designed by controlling the multilayer materials. In this paper, a more fundamental study of In-Ag solder materials is carried out in chip-to-chip level by using flip-chip based thermocompression bonding. Bonding at 180°C for various time duration under various bonding pressure is studied. Approaches of forming Ag2In with re-melting temperature higher than 400°C at the bonding interface are proposed and discussed. Knowledge learned in this process technology can support us to develop sophisticated wafer level packaging process based wafer bonding for applications of MEMS and IC packages.