2008 Volume 11 Issue 2 Pages 141-146
A novel Bi-base solder for mounting semiconductor power devices on inverters used in hybrid and fuel-cell vehicles was studied. The solder consists of Bi-base matrix (m.p. (melting point) =270°C), which facilitates high-temperature soldering, and dispersion particles of a Cu-Al-Mn alloy, whose thermoelastic martensitic microstructure is expected to relax the thermal stress. The tensile strength of the developed solders was found to be remarkably improved compared with that of pure Bi. Results of tensile tests at elevated temperatures showed greater elongation and lower strength than those at room temperature. However, sufficient tensile strength was still remained at 195°C. Effects of the CTE (coefficient of thermal expansion) and the surface substance of chips and substrates on the IMC (intermetallic compound) formation and thermal cycling properties were investigated. Even after 1983 thermal cycles between -40°C and 200°C, neither intermetallic compounds nor cracks were observed at the Cu/Bi-base solder interfaces in the CTE matched samples.