Failure Probability Estimation of Anisotropic Conductive Film Packages With Asymmetric Upper-to-Lower Pad Size and Misalignment Offsets

Anisotropic conductive films (ACFs) are widely used in the packaging of flat panel displays and liquid crystal displays and for attaching bare chips to both flexible and rigid substrates. This paper utilizes the V-shaped curve method to analyze the failure probability of ACF packages with an asymmetric upper/lower pad size and misalignment offsets. In the proposed method, the probability of opening failures is modeled using a Poisson function, modified to take into account the effects of the pad-width difference and misalignment offset on the effective conductive area between opposing pads. Meanwhile, the probability of bridging failures is evaluated using an enhanced bridging model based on the distance between the neighboring pad pairs in the array. The failure probability of the pad array is evaluated as a function of both the difference in width of the upper and lower pads and the degree of misalignment between the opposing pads in the array. The results show that the V-shaped curve method provides the means to predict the ACF volume fraction which minimizes the failure probability of the ACF assembly given a knowledge of the pad-width difference and the misalignment offset. In addition, it is shown that when the misalignment offset is greater than the pad-width difference, the minimum failure probability reduces as the pad-width difference increases due to the corresponding increase in the effective conductive area between opposing pads. Conversely, when the misalignment offset is less than the pad-width difference, the minimum failure probability increases with an increasing pad-width difference due to the corresponding reduction in the effective conductive area between the pads.