Influence of Pad Design on Assembly Reliability of Surface Mounted Devices

During the reflow process in surface mount technology (SMT), a passive component misplaced on a pad would be self-aligned or tombstoned due to a restoring force which is driven by surface tension of molten solder. In this study, the influence of pad design on assembly defect rate was experimentally and analytically investigated using computational fluid dynamics (CFD) simulation. The assembly defect rate of the SMT was experimentally derived from the design of experiments (DOE) considering the pad design and the misplacement of the passive component. The restoring force and moment acting on the chip resistor were calculated using CFD simulation considering the fluidic forces of the molten lead-free solder paste during the reflow process according to the amount of the misplacement and the pad design parameters.