Modeling and evaluation criterion for thermocompression flip-chip bonding

A single joint finite element model (FEM) using a newly developed configuration independent evaluation criterion has been created, and experimentally verified, to provide more accurate predictions of bond formation based on the joint design and assembly process parameters. This model is based on the joint interface mechanics resulting from joint bump compression. Previous studies used a deformation criterion that depended on a specific joint configuration to evaluate the effectiveness of the expected bond. This limited the applicability of the model results to the joint design for which the deformation criterion had been experimentally determined. The technique reported in this research, uses finite element models to compute detailed distributions of stresses/strains at the interface of a joint when it is plastically deformed under compression. The evaluation criterion is defined to be the change in the differential area at the bonding interface, and is shown mathematically as follows: ΔA=ε_xx+ε_yy≥(ε_xx+ε_yy)_crit. Models using this criterion allow for the comparison of the effects of various joint design and manufacturing process parameters on the bond joint mechanics, and the resulting probable bond joint quality. A determination of the minimum deformation required for joint formation can be obtained for any design within specified limits.