The Influence of Alloy Composition and Heat-Treatments on the Shape Memory Properties in a Cu-Sn-X Alloy

We have focused on shape-memory properties of Cu-Sn based ternary alloys in this study. We have attempted to suppress degradation at room temperature aging and to improve the amount of shape recovery by adding the third element to a binary Cu-Sn alloy. The attempt has successfully conducted in Cu-Sn-Mn alloy, the degradation due to aging at room temperature was suppressed and the thermal stability was improved. Furthermore, the present study revealed that Cu-Sn-Mn alloy exhibited a large super elastic recovery in three point bending tests. We have also investigated the shape-memory properties of Cu-Sn-Si alloys and revealed that the ternary alloy has achieved super-elastic recovery better than the Cu-Sn-Mn alloy in the three-point bending tests.

Effect of Long-Term Room Temperature Aging on the Fatigue Properties of SnAgCu Solder Joint

Solder joints in electronic assemblies are subjected to mechanical and thermal cycling. These cyclic loadings lead to the fatigue failure of solder joints involving damage accumulation, crack initiation, crack propagation, and failure. Aging leads to significant changes on the microstructure and mechanical behavior of solder joints. While the effect of thermal aging on solder behavior has been examined, no prior studies have focused on the effect of long-term room temperature aging (25 °C) on the solder failure and fatigue behavior. In this paper, the effects of long-term room temperature aging on the fatigue behavior of five common lead-free solder alloys, i.e., SAC305, SAC105, SAC-Ni, SAC-X-Plus, and Innolot, have been investigated. Several individual lead-free solder joints on printed circuited boards with two aging conditions (no aging and 4 years of aging) have been prepared and subjected to shear cyclic stress–strain loadings until the complete failure. Fatigue life was recorded for each solder alloy. From the stress–strain hysteresis loop, inelastic work and plastic strain ranges were measured and empirically modeled with the fatigue life. The results indicated that 4 years of room temperature aging significantly decreases the fatigue life of the solder joints. Also, inelastic work per cycle and plastic strain range are increased after 4 years of room temperature aging. The fatigue life degradation for the solder alloys with doped elements (Ni, Bi, Sb) was relatively less compared to the traditional SAC105 and SAC305.