SRI International has used three-dimensional nonlinear finite element analyses to analyze the response of solder joints to various types of mechanical and thermal loading. Figure 1(a) shows the finite element mesh used for an analysis of the shock response of a device with J leads. The device was subjected to a high acceleration pulse. The resulting stresses in the leads and solder joints are shown in Figure 1(b). These analyses are used to evaluate the shock resistance of existing electronic devices and to design components with improved shock resistance.

We have also performed analyses to investigate the fatigue response of solder joints to mechanical and thermal cycling. For these analyses we developed a visco-plastic creep model for solder response in which solder fatigue damage is calculated as part of the constitutive model. We also developed analyses to predict fatigue life from finite element calculations. Figure 2 shows calculated fringes in damage for two lead configurations, a high stiffness lead and a low stiffness lead. The high calculated damage for the high stiffness leads predicts low cycle mechanical failure for that configuration.

Figure 1 Solder Joint Pulse Loading J-Lead Device Subjected to a Pulse Load

Figure 2 Solder Joint Thermal Fatigue Analysis of Thermal Cycling for J-Lead Solder Joints

C.G. Schmidt, J.W. Simons, C.H. Kanazawa, and D. Erlich, "Thermal Fatigue Behavior of J-lead Solder Joints," IEEE Transactions on Components, Hybrids, and Manufacturing Technology Part A, Vol. 18, No. 3 (September 1995).