Reliability of Self-Assembly Vertical Interconnects in Magnetically Aligned Anisotropic Conductive Adhesive for Electronic Packaging Applications

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 input-output pads and particles. In order to characterize self-assembly vertical interconnects created in an MA-ACA, quad-flat no-lead chips with 40 daisy chain pads were assembled on a printed circuit board. In reliability tests, the dc resistance of self-assembly test samples was observed to be 35.9% and -12.1% changed at temperatures of 85°C and -55°C, respectively, after 700 thermal shock cycles and 0.4% changed after an 8-h vibration test. In contrast, the dc resistance was observed to be significantly 41.4 Ω increased due to humidity absorption after an 85°C temperature-85% humidity test for 500 h. 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 a thickness of 10 μm was observed to be greatly 85.2% reduced after an 85°C temperature-85% humidity test. In addition, based on a Weibull distribution model, the mean time to failure of self-assembly vertical interconnects was estimated to be importantly 94.7% improved. Consequently, the proposed self-assembly packaging using a Parylene material is applicable to cost-effective electronic applications.