Empirical Equations for Optimization Conditions in Thermal Compression Bonding of Copper Pillar Flip Chip Packages

Abstract

In this paper, finite element simulations are used to analyze the plastic deformation of the solder ball and its stress and strain distributions. The bonding forces that depend on the forming temperature are investigated. The contact areas between the solder ball and the copper trace are also discussed. The largest contact area is regarded as the optimization condition during the thermal compression bonding processes. The effects of different pillar-trace shift ratios on the contact areas are also discussed to provide a guideline for avoiding product failure. Finally, an empirical equation adopting a four-parameter logistic nonlinear regression model for the pillar-trace gap in terms of the forming temperature and bonding forces is established.