PLASTIC-DEFORMATION OF SOLDER JOINTS IN PIN GRID ARRAYS SUBJECTED TO THERMAL-STRESS

In an earlier work [I], thermal stresses in soldered pins were calcula ted under the assumption of apr elastically deforming solder barrel In the present analysis, the nonlinear, temperature dependent stress-str ain 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 Delta T(e.g., 0-100 degrees C) is divided into a finite number II of temperature stages, and the final responses are superposed from the n contributions each of which done u sing 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. Compari sons with elastic solder foundation calculation results show that ther mal and inelastic solder stress/strain dependence should be included e specially in the higher (over 75 degrees C) temperature range.