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

Abstract

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 R h 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 R h = 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.