Tin pest in Sn-0.5 wt.% Cu lead-free solder

Tin pest (the product of the allotropic transformation of beta -tin into al pha -tin at temperatures below 286 K) has been observed in a Sn-0.5 wt.% Cu solder alloy. Some 40 percent of thr specimen surface was transformed into gray tin after aging nt 255K for 1.5 years, and after 1.8 years, the propo rtion increased to about 70 percent. The degree of transformation in work-h ardened areas is much higher than in other areas, suggesting residual stres s might provide an additional driving force for the transformation into alp ha -tin. The allotropic change results in a 26 percent increase in volume, and cracks are initiated to accommodate the changes in volume. Results indi cate that tin pest could lend to total disintegration of micro-electronic s older joints. The tin-copper eutectic system may become a prominent Iran-fr ee solder, and fin pest could have major ramifications on service lifetime of electron assemblies.