Copper wire bond analysis: Pad design effects and process considerations

In this paper, the fundamental understanding of copper (Cu) wire bonding process, and its interaction with the die bond pad surface and structure will be examined, using both Finite Element Analysis (FEA) and experimental study. In the FEA, the Cu wire bonding process is modeled based on dynamic analysis using commercial available finite element software, to investigate the capillary geometry and the bond pad structure designs. In the experimental study, four different factors are evaluated; 1) the inner chamfer angle (ICA) of the capillary, which can affects the ball bond shape formation; 2) the Al pad thickness, and 3) die bond pad coating, which can affects the Al squashing; lastly, 4) the die bond pad structure.