Failure analysis of pad-height effects in the fine-pitch interconnection of the anisotropic conductive films

This study analyzes the effect of the upper-to-lower pad-height ratio on the global failure probability of IC/substrate assemblies packaged using Anisotropic Conductive Film (ACF). In modeling the failure of the IC/substrate package, the probability of an opening failure in the vertical gap between the pads is calculated using a Poisson function, while the probability of a bridging failure between the pads in the pitch direction is computed using a modified box model. The opening and bridging probabilities are then combined using probability theory to establish an overall failure prediction model for the IC/substrate assembly. The results show that the failure probability increases as the sum of the lower pad height and upper pad height increases, or as the ratio Rh of the upper pad height to the lower pad height increases. Furthermore, for a given gap size between the IC device and the substrate, the minimum failure probability is obtained when the ratio of the upper pad height to the lower pad height has a value of Rh = 1. Overall, the results suggest that the reliability of ACF-packaged IC/substrate assemblies can be improved by reducing the total height of the two pad arrays or by utilizing pad arrays with an equivalent height.