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.
Analysis of new anisotropic conductive film (ACF)
This paper designs a new multilayered particle anisotropic conductive film (ACF) compound. Using the particle-reinforced composite model and probability theory, the novel ACF compound is compared with three traditional ACFs having the same particle volume fraction. The particle-reinforced model applies the concept of bonded and debonded structures in the interfaces between the adhesive resin and the particles. The elastic modulus of the particle-reinforced ACF is a function of the particle volume fraction and the bonded condition. In the failure model, probability theory is used to calculate the probability of opening and bridging. The volume fraction of the conductive particles plays an important role in determining the optimal ACF design. The current results indicate that the flip chip packaging performed using the novel multilayered particle ACF compound (particles distributed in the top/bottom surface layers) exhibits superior particle-reinforcement properties and a lower failure probability than traditional ACFs. The improved understanding of reinforcement mechanisms and failure probability developed by this study facilitates the enhanced design of novel ACF compounds.
Distribution function for random distribution of spheres
THE statistical problems associated with a distribution of spheres in space have received considerable attention1–3, particularly in the limiting cases of very small volume concentrations and very large ones (close to maximum packing). The intermediate range of finite concentration is not as well covered, and this range is considered here.