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This paper utilizes the V-shaped curve method to analyze the failure probability of anisotropic conductive film (ACF) packages with various degrees of IC/substrate misalignment. In evaluating the failure probability of the ACF package, the probability of an opening failure in the vertical gap between the pads is determined in accordance with a Poisson function, while the probability of a bridging failure between the pads in the pitch direction is computed using a bridging model. In computing the opening and bridging probabilities, the Poisson function and bridging model 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 an overall failure prediction model for the IC/substrate assembly. It is shown that, for any given value of the IC/substrate misalignment, the modified V-shaped curve method enables not only the failure probability of the ACF package to be reliably predicted but also an estimate to be made of the optimal ACF volume fraction. The results show that the semilogarithmic failure probability increases approximately linearly with the volume fraction for both uni- and bidirectional misalignments of the ACF package. The optimal volume fractions for ACF packages with misalignments not considered in this paper can be derived from the current results via a process of interpolation.
Device and Materials Reliability, IEEE Transactions on (Volume:10 , Issue: 1 )
Date of Publication: March 2010