Microstructure of Sn-Ag-Cu lead-free flip chip interconnects during aging

In the electronic industry flip chip has been the primary technology used in chip interconnection process. Its tiny solder joint includes complicated structures such as Sn solution; eutectic mixture and intermetallic compounds (IMCs), whose mechanical performance is quite different from the original solder bulk. In this paper, the microstructure evolution of flip chip solder joints under thermal aging was analyzed. The results showed that with the aging time increasing, coarsening of solder bulk matrix and AuSn₄ occurred, and large IMCs formed near the interface after aging for some time, but disappeared again when the aging continued. The interfacial morphology between IMC and solder bulk became more planar after aging. Influence of reflow times in butted bonding (as-bonded condition) on the characteristics of interfacial IMC is weakened as the process of aging going.