Effect of thermal treatment on fracture behavior of solder joints at various strain rates: Comparison of cyclic and constant temperature

Abstract

Fracture tests on Sn93Pb37 solder joints in a double cantilever beam (DCB) configuration were performed at two different strain rates of 10−5 and 0.03 s−1 under mode I loading conditions. In each case, the critical strain energy release rate for crack initiation, Jci, was obtained. Effects of storing specimens at a constant temperature of 75 °C and cyclic temperature varying between 32 and 75 °C were examined at these strain rates. In the strain rate of 0.03 s−1, storing samples in a constant or cyclic temperature caused the fracture energy to decrease significantly with respect to the specimens maintained in ambient temperature. The significant reduction in fracture energy by placing the samples at high temperatures in the intermediate strain rate was due to the considerable rise in IMC layer thickness. Also, in this strain rate, the decrease in fracture energy under the constant thermal condition was greater in comparison to the thermal cycling case. This behavior was attributed to microstructural differences in the solder layer of samples; in the specimens aged at a constant temperature of 75 °C, Cu6Sn5 and Cu3Sn phases were observed in the solder joint microstructure. No such phases formed in the samples experienced the thermal cyclic profile. In quasi-static loading conditions, however, the fracture energy in cyclic and constant thermal conditions was approximately equal with the fracture energy of the sample stored in ambient temperature. In both thermal conditions, fracture energy increased significantly by rising the strain rate from quasi-static (i.e. 10−5 s−1) to 0.03 s−1. Moreover, the influence of strain rate was greater in cyclic thermal condition compared to constant thermal condition.