Solid/solid state interfacial reactions in the lead-free solders/Cu-2.3%wt. Fe alloy (C194) couples

Background: Lead-free solders (LFSs) involve incorporating trace elements into Sn, resulting in alloys like Sn-3.0 wt.% Ag-0.5 wt.% Cu (SAC) and Sn-0.7 wt.% Cu (SC). These solder have similar properities to Sn-Pb solders. C194, renowned for its exceptional corrosion resistance, high strength, and good weldability, serves as a preferred lead-frame material in electronic packaging. In this study, we investigated the solid/solid state interfacial reactions between the LFS and Cu-2.3 wt.% Fe alloy (C194). Methods: Three LFS including Sn, SAC, and SC were first reflowed with C194 to form the LFS/C194 couple. Then the LSF/C194 couples were aged at 125-175 degrees C for 100-2000 h. Significant findings: The results revealed that only the (Cu, Fe)6Sn5 phase was formed in the Sn/C194 couple aged at 125 degrees C. At higher temperatures and longer aging times, the (Cu, Fe)3Sn phase was formed in all three couples. The Fe addition into Cu could inhibit the (Cu, Fe)3Sn phase growth. Kirkendall voids in this study occur more frequently with the increase in aging temperatures and times, but the intensity varies in each system. Meanwhile, the thickness of total intermetallic compound (IMC) was increased with the increase in aging times and temperatures in these three couples. The IMC growth mechanism is diffusion controlled in all LFSs/C194 couples.