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A self-assembly process in a magnetically aligned anisotropic conductive adhesive (MA-ACA) is a novel approach to selectively create high-density vertical interconnects by magnetic interaction between ferromagnetic I/O pads and particles. In order to characterize self-assembly vertical interconnects created in an MA-ACA, quad-flat-no-lead (QFN) chips with 40 daisy-chain pads were assembled on a printed-circuit board (PCB). In reliability tests, the DC resistance of self-assembly test samples was observed to be 35.9% and -12.1% changed at a temperature of 85aC and -55aC after 700 thermal-shock cycles and also 0.4% changed after an 8-hour vibration test. In contrast, the DC resistance was observed to be significantly 41.4 Ç increased due to humidity absorption after an 85aC temperature-85% humidity test for 500 hours. Thus, in order to prevent humidity percolation in the self-assembly vertical interconnects, a Parylene-C material was used as a barrier layer. The DC resistance change of Parylene-deposited test samples with 10-Ým thickness was observed to be greatly 85.2% reduced after an 85aC temperature-85% humidity test. In addition, based on a Weibull distribution model, a mean-time-to-failure (MTTF) of self-assembly vertical interconnects was estimated to be importantly 94.7% improved. Consequently, a proposed self-assembly packaging using a Parylene material is applicable to cost-effective electronic applications.
Device and Materials Reliability, IEEE Transactions on (Volume:PP , Issue: 99 )