Analysis of TAB inner lead fatigue in thermal cycle environments

The inner leads of a Tape Automated Bonding (TAB) device can be subject to early fatigue failures in thermal cycle environments. This paper describes a 3-D non-linear finite element analysis of the failure mechanism, and verifies the results by experiment. Some TAB applications require environmental qualification and electrical testing in the unexcised tape carrier or retain a significant portion of the polyimide tape in the assembly. In these cases the Coefficient of Thermal Expansion (CTE) mismatch between the silicon die and polyimide tape can cause plastic strains in the inner leads. Several design variations are quantified. Those with first order effects were found to be encapsulant material, lead length, and lead material