A review of Pb-free high-temperature solders for power-semiconductor devices: Bi-base composite solder and Zn-Al base solder

Pb-base high-temperature solders (mass % Sn=5-10, melting point (m.p.)=300-310°C) are widely applied under severe conditions, although the harmful nature of Pb is recognized. Bi-base alloys (m.p. of Bi=270°C), Zn-base alloys (m.p. of Zn=420°C), and several Au-base eutectic alloys (m.p. of Au-20Sn and Au-3.6Si=280 and 363°C, respectively) are proposed as candidates for Pb-free hightemperature solders. This paper reviews the features of Bi-base composite solders containing reinforcement particles of a superelastic Cu-Al-Mn alloy in a Bi matrix to relax thermal stress and to prevent the propagation of cracks, and Zn-Al base solders, which have high stability and high reliability enough to be utilized in practical applications under severe thermal cycle tests between-40 and 230°C more than 2000 cycles.