Microstructural evolution and mechanical properties of Sn-Bi based solders

Abstract

An overview of issues relevant to reliability of Sn-Bi solder joints is presented. The effects of aging on the microstructure of Sn-Bi solder joints are described. The results show that during aging, Sn is depleted from the solder/base metal interface. The two-phase Sn-Bi microstructure coarsens appreciably during aging. The rate of coarsening can be slowed by adding 1.0 wt% Cu to the solder. Aging also affects the mechanical properties of the solder joints in shear, where aged joints shown an increase in flow stress and plastic strain at failure. The creep properties of cast and aged Sn-Bi eutectic alloy at stresses between 0.5 and 65 MPa and temperatures between 30/spl deg/C and 120/spl deg/C are described. In the power law creep regime, cast Sn-Bi eutectic has a stress exponent of three and an activation energy of 0.6 eV.<>