Abstract
The thermal cycle test was performed to CSP microjoints with several Sn-Ag lead-free solders, and the microstructure observation was performed before and after thermal cycle test. In the initial solder joints with Sn-3.5Ag or Sn-3.5Ag-0.76Cu, fine Ag3Sn grains were mainly distributed at the grain boundary of Sn and around there. Those grains formed the network structure in the Sn matrix. After thermal cycle test, a spherical growth of Ag3Sn grain was observed and the network structure was disappeared. In that microstructure, the crack growth was relative fast. On the other hand, as for Sn-Ag-Bi-Cu alloy, Bi phases were finely existed in Sn matrix and those were stable even after the thermal cycle test. The crack growth in Sn-Ag-Bi-Cu solder was relative slow because of the stable microstructure.
