Approximate solutions for the stresses in the solder joints of a printed circuit board subjected to mechanical bending

The increasing occurrence of drop-impact failure of portable electronics could be traced to the failure of the solder joints that interconnect the integrated circuit (IC) components to the printed circuit board (PCB)—collectively referred to as PCB assembly. The drop impact leads to bending of the PCB assembly within the portable electronics, and the interconnecting solder joints undergo severe deformation to accommodate the differential bending deformation between the IC component and the PCB. This manuscript presents an approximated closed-form analytical solution for the stresses in the solder joints of the PCB assembly subjected to mechanical bending. The PCB assembly is modelled as a tri-layer structure in which the IC component and the PCB are modelled as beams or plates and the solder joints as a continuous layer consisting of infinite number of beams that are capable of carrying normal force, shear force, and moment along its interfaces with the IC component and the PCB. The analytical solutions have been validated against finite element analysis. Design analysis has suggested that the robustness of the PCB assembly against mechanical bending can be increased by increasing the diameter of the solder joints; increasing the in-plane and flexural compliances of IC component and PCB; while reducing the shear and flexural stiffness of the solder joints and reducing the transverse compliant of the PCB assembly.