Analysis of the viscoplastic behavior of Pb-free solder using lap shear joints

Abstract

The single lap shear tests were conducted on the most popular lead free solder alloy at two different shear strain rates (γ̇=0.01 s−1 and 0.00001 s−1) in combination with three different temperatures (T = 25°C, 75°C, and 125°C) to determine the viscoplastic model parameters utilizing the shear stress-strain data. The yielding of shear stress-strain curves was predicted and a unified viscoplastic model was proposed to calculate the entire shear stress-strain curves using material parameters and shear modulus. The shear stress-strain curves, which were obtained through lap shear tests and calculated by the model, show a very good relationship. Moreover, a finite element model, which was developed to create a lap shear simulation, calculates the shear stress-strain curves that make a reasonable agreement with the experimental data too. Plastic work/volume for monotonic lap shear and hysteresis curves for cyclic lap shear that are important parameters for predicting crack initiation and propagation of solder joint were calculated using a finite element model. As predicted, the variation of plastic works and hysteresis curves were observed due to strain rate and temperature changes. A thermal cycling simulation, which was created by utilizing the finite element model of lap shear specimen, demonstrates accumulation of plastic work occurred during ramping step rather than dwelling step.