Electrical characterization and reliability assessment of lead-free solder coated electrical contacts

Elimination of lead from electronics is a global phenomenon driven by both legislation and market forces. The European Union has set July 2006 as the deadline for eliminating tin-lead solder from most electronic products. Extensive studies on lead-free solders for device and product interconnections are going on worldwide. However lead-free solders are also expected to replace tin-lead solders as contact finishes for electronic contacts.; In this study, the electrical performance of tin-silver-copper and tin-copper coatings was investigated and compared with tin-lead eutectic coating. The contact resistance after different aging conditions, including mixed flowing gas, steam, and dry heat aging, was examined. Energy Dispersive Spectroscopy (EDS) analysis was conducted to determine the nature of the surface films in the aged samples. EDS results suggest that tin-silver-copper lead-free solder coating is not sensitive to corrosive gases like chlorine and hydrogen sulfide in light industrial environment. Tin-silver-copper and tin-lead alloy coatings have similar performance on contact resistance versus contact normal force after dry heat aging and MFG aging. Severe degradation was found on tin-silver-copper coatings after steam aging. Higher contact force is suggested in the application of tin-silver-copper solder alloy coating than for eutectic tin-lead alloy coatings.; Fretting corrosion was studied for tin-silver-copper and tin-copper lead-free alloy coatings and compared with tin-lead coating. Fretting corrosion experiments were conducted and compared at different temperatures (25°C, 50°C, 80°C), difference normal forces (20g, 50g, 80g), and different fretting amplitudes (10μm, 15μm, 25μm, 40μm). Cycles to failure of each test were recorded. A Weibull distribution was used to best fit the experimental data. Mean cycles to failure (MCTF), and cycles to 1% and 10% failure were calculated for each material at each fretting condition. Comparisons were made among the materials. In general, tin-silver-copper and tin-copper alloys show better or similar fretting corrosion resistance than tin-lead eutectic alloy at the experimental conditions in this study.