11 - Stresses in solder joints due to the bending deformation of printed circuit boards in microelectronics assemblies

Abstract

This chapter is focused on analytically establishing the stresses acting on the solder joints interconnecting the microelectronic assembly to the printed circuit board (PCB) when a PCB assembly undergoes flexural deformation. The differential flexural deformation between the microelectronic assembly and the PCB has to be accommodated by the interconnecting solder joints leading to high magnitude of stresses in the solder joints. The analytical solution of stresses in the solder joints is an extension of the advanced model presented in Chapter 2 for the modelling of interfacial stresses due to mismatched thermal expansion, with an additional term that describes the bending of solder joints. Design analysis using the advanced solution has led to many useful insights for robust design of solder joints against mechanically induced PCB bending. For example, design analysis using the analytical solution has suggested that the peeling stress in critical solder joint could be reduced by increasing its cross-sectional area and its flexural compliance. By reducing the volume of the critical solder joint during solder printing and hence into an hourglass shape, it has been shown experimentally that the critical solder joint’s fatigue life at high strain rate has been doubled.