Plastic Deformation of Solder Joints in Pin Grid Arrays Subjected to Thermal Stress

Abstract

In an earlier work [1], thermal stresses in soldered pins were calculated under the assumption of an elastically deforming solder barrel. In the present analysis, the nonlinear,temperature dependent stress-strain curve of solder, without creep, is taken into account, yielding an elasto-plastic foundation modulus function. For the thermal mismatch loading, the total temperature range ΔT (e.g., 0–100°C) is divided into a finite number n of temperature stages, and the final responses are superposed from the n contributions each of which done using an isothermal stress calculation. Three solders (Sn-Pb solders 63/37, 70/30, and 10/90), were investigated; the solder barrel thickness and mismatch temperature range were also variable parameters. Comparisons with elastic solder foundation calculation results show that thermal and inelastic solder stress/strain dependence should be included especially in the higher (over 75°C) temperature range.