Constitutive Behavior and Low Cycle Thermal Fatigue of 97Sn-3Cu Solder Joints

Abstract

The thermal cyclic shear stress/strain hysteresis response and associated steady-state creep parameters of 97Sn-3Cu solder joints have been determined using a beam specimen previously developed by Pao et al. (1992a). The solder joint was subjected to a 40-minute thermal cycling from 40°C to 140°C. A constitutive equation based on elastic and steady-state creep deformation for the solder has been formulated and implemented in a finite element program, ABAQUS, to model the experiment. The results show that the constitutive equation based on one single creep mechanism cannot fully account for the deformation during cooling, as opposed to the case of 90Pb-10Sn where the entire cyclic deformation can be well modeled by a similar constitutive equation (Pao et al., 1992c). This suggests that another creep mechanism is dominant for lower stresses and higher temperature. The thermal fatigue results show that the failure mechanism of 97Sn-3Cu joints is similar to that of 90Pb-10Sn joints, but the number of cycles to failure of 97Sn-Cu solder joints is at least 5 times longer than 90Pb-10Sn solder joints. This indicates the potential application of 97Sn-3Cu in place of 90Pb-10Sn solder.

Constitutive Relations for Creep in a SnCu-Based Composite Solder Reinforced with Ag Particles

“…Since the shear modulus is not sensitive to the microstructure, a good approximation of calculation on the normalized stress can be obtained by employing the shear modulus of pure Sn. 16 The shear modulus of pure Sn can be calculated from the elastic modulus E, which can be described as 17 :…”

Temperature Dependence of Creep and Hardness of Sn-Ag-Cu Lead-Free Solder

“…In the studies by Guo et al 14 and Pao et al, 15 the shear modulus of the Sn-4Cu-0.5Ag 14 and the 97Sn-3Cu 15 solders were both assumed to be equal to that of pure Sn, which resulted in a good approximation in the calculation of the normalized stress. In the present study, the effect of temperature on creep and hardness of the Sn-Ag-Cu leadfree solder using the nanoindentation method were investigated.…”

Quick assessment methodology for reliability of solder joints in ball grid array (BGA) assembly—Part I: Creep constitutive relation and fatigue model

“…With the assumption that the creep deformation mechanism does not change at the temperature range of -40~ to 150~ some researchers [2,3,5] suggest that the activation energy is kept constant for the whole temperature range studied. Under logarithmic coordinates, Eq.…”

“…Simple Arrhenius power-law creep constitutive relations [ 2,3] have been widely employed to predict the high temperature creep flow of Sn-Pb solders during past fifteen years. However, those relations were found to break down at high stresses and are incapable of explaining the issues that the values of stress exponent and activation energy are temperature dependent [ a].…”