Simulation of thermal stresses in 2N gold wires evaluated for PBGA application

Simulation of thermal stresses in gold wires was rarely reported in previous days due to the difficulties in FE model building. In this study, the 3D modeling was performed to evaluate the thermal stresses in gold wires with the entire package model to identify which wires to peel when verifying the second bond. The FE model in this study included the wire loops and the second bond (stitch bond) geometries surrounded by the molding compound. The 2N RelMax gold wires were evaluated for PBGA application with discussing the modeling results on Von Mises stress, equivalent plastic strain and peeling stress. The condition of TC (temperature cycle) test was applied in this modeling. The simulation results indicated that shorter wires had higher stress than longer wires. Maximum equivalent plastic strain was observed on shorter corner wire(s). Thus, shorter corner wire(s) had the highest propensity to fail in TC. Maximum peeling stress on bonding interface among all wires was located at the tail end of the stitch bond of the shorter corner wire(s). It might indicate that the shorter corner wire(s) had higher priority to be selected to perform the wire peel test. Different from the other wires, the highest peeling stress on bonding interface for the shorter center wire(s) was at the wire heel location instead of the tail end of the stitch bond. The wire heel location was usually regarded as the sensitive region related with the initial crack leading to the stitch bond failure. Therefore, the shorter center wire(s) should be also considered with high priority to be wire peeled to document the wire peel specification.