TENSILE TEST FOR ESTIMATION OF THERMAL FATIGUE PROPERTIES OF SOLDER ALLOYS

A tensile test is proposed to evaluate the thermal fatigue resistance of solder alloys. The test is based on the strain rate change method t o obtain the strain rate sensitivity index, m. The m value is obtained at various strains during the tensile test. The plots of m and strain where m is measured showed a linear relation; therefore, the m value at zero strain, m(0), and the gradient, k, are obtained by extrapolati on. The m value at zero strain related to the coarseness or fineness o f solder alloy microstructure; m(0) becomes lower with coarsening of t he microstructure. The solder alloys with low m(0) and low k have exce llent thermal fatigue resistance when compared with alloys with high m (0) and high k. m(0) and k would be good measures to estimate the ther mal fatigue properties of solder alloys; highly resistant alloys have low m(0) and low k.