Characterization and Comparison of Five SAC-based Solder Pastes for Pb-free Reflow Soldering

Based on literature review and industry survey, five types lead-free solder pastes, namely, SAC305 (96.5%Sn-3.0%Ag-0.5%Cu), SAC387 (95.5%Sn-3.8%Ag-0.7%Cu), SACS (96.2%Sn-2.5%Ag-0.8%Cu-0.5%Sb), SCN (99.3%Sn-0.7%Cu-0.05%Ni), and SACC (96.4%Sn-3.0%Ag-0.6%Cu-0.01%Ce) are studied in this paper. The basic properties of selected Pb-free solder pastes are tested based on IPC standards. These tests include solder paste particle size analysis, measurement of melting point, solder balling test, tack test and slump test. The reflow temperature profiles for these five types of solder pastes are set up and surface mount parameters are optimized according to their characteristics. Solder reflows with nitrogen and without nitrogen are performed for comparison. Intermetallic compounds of different solder alloys on both ENIG and OSP pad finishes are investigated. Cross-sectioned samples are inspected by SEM/EDX. The related results of each test are presented.