Linkage-spring model in analyzing wirebonding loops

Several wirebonding loops were proposed to prevent the necking in wire. Mos t of experimental statistical methods were applied in the analysis of wireb onding and it was time consuming and without the precise analysis. Further, the finite element analysis is the most powerful tool for stress analysis; however, it is too complex for analyzing a large deformation. Hence, this paper proposes a novel method using springs to simulate the condition of fo rces acting on a section of the bonding wire. The bonding wire profile can be formed by combining several sets of linkage with springs, wherein the co efficients of elasticity and plasticity of the springs are determined by th e bending angle of two linkages which simulates the elastic-plastic deforma tion of the bonding wires. The operational model can be simplified by using the multiple degrees of freedom of the linkages/springs to analyze the pro file and forces of the bond wire. Experiments have been conducted to valida te the model. Good agreement is obtained between analytical prediction and experimental data. Finally, three basic preforms for wirebonding are introd uced, and it can be seen that the loop sagging at the second bond is improv ed and the loop height can be controlled by proper design. Necking and frac ture during the bonding process can be avoided by the present method and th e optimum wire bonding profiles can also be achieved.