Study of wire bonding looping formation in the electronic packaging process using the three-dimensional finite element method

摘要

This paper presents a three-dimensional finite element model of the thermosonic wirebond looping process. The gold wire heat affected zone load-displacement relationship was investigated using precision micro-force tensile tests. The temperature-dependent elastoplastic behaviors of gold wire were taken into account in the nonlinear finite element model. Both the solid and equivalent shell wire models were used; exhibiting very close agreement, indicating that equivalent model was adequate. The simulation results were verified against the experimental results. The standard triangle loop (STD2-Mode) and trapezoidal loop (LOW2-Mode) were simulated. The finite element model closely predicted the profile of the tested loops. This model was used for an extensive looping factor parameter study. No obvious looping parameter effects were observed for the STD2 Mode. The loop shapes depend primarily on the wire properties, bonding pad distance and tier height. Both the looping and material parameters have significant effects on the loop shape for the LOW2 Mode. Optimizing the reverse angles could reduce the stress on the wire.