Thermal and mechanical reliability of low-temperature solder alloys for handheld devices

Low temperature alloys are used to achieve peak reflow temperatures from 170 to 200°C. Sn-Bi alloy stands as logic choices due to its low melting point, higher strength and low cost. However, use of Sn42-Bi58 alloy as soldering material is limited by a series of drawbacks such as low ductility, and poor thermal and mechanical reliability. Here we show how the use of micro-additives in eutectic Sn-Bi alloys improves thermal fatigue and mechanical shock properties. The basic properties of the new alloys shown here were fully characterized and their use in SMT applications evaluated, especially in drop shock and temperature cycling tests. Among the new alloys proposed, alloy B demonstrates superior mechanical properties, thermal cycling, drop shock and creep resistance, against benchmarks. Use of this new alloy in applications such as portable devices, PV ribbons and high efficiency LEDs will be highly beneficial due to its superior performance.