Effects of Pad Array Dimensions and Misalignment Offsets on Optimal Fraction of Conductive Particles in Anisotropic Conductive Film Packages

The failure probability of anisotropic conductive film (ACF) packages is critically dependent on the volume fraction of conductive particles within the adhesive resin. In this study, the V-shaped curve method is used to determine the optimal volume fraction of conductive particles as a function of the bonding geometric parameters, the pad array dimension, and the misalignment offset between the upper and lower pads. In evaluating the corresponding failure probability of the ACF package, the probability of an opening failure is determined in accordance with a Poisson function model, while the probability of a bridging failure is derived using a box model. In computing the opening and bridging probabilities, the two models are modified to take account of the effects of package misalignments on the effective conductive area between opposing pads and the bridging path length between neighboring pairs of opposing pads, respectively. The opening and bridging probabilities are then combined using probability theory to establish the overall failure probability of the ACF package. In general, the results show that, for given bonding geometric parameters and misalignment offset, the optimal volume fraction of conductive particles remains approximately constant as the pad array dimension is increased. However, for given bonding geometric parameters and pad array dimension, the optimal volume fraction of conductive particles increases with an increasing misalignment error. Overall, the results show that, for any given values of the bonding geometric parameters, pad array dimension, and misalignment offset, the failure probability of the ACF package can be minimized by setting the volume fraction of conductive particles equal to the value corresponding to the tip of the V-shaped curve.