Development of PEB face-down interconnection process for ultra thin flexible package

System in Foil (SiF) package could realize flexible, multi-functional and higher performance package using flexible substrate and ultra-thin heterogeneous chip integration. In this study, PEB(polymer elastic bump) bonding process is suggested newly, which could reduce stress concentration remarkably near bump and chip face by soft polymer bump material with electro-conductive metal line pattern and usage of NCF(non-conductive adhesive film) and also lower bonding temperature during face-down interconnect process between flexible substrate and ultra-thin chip. Compared to conventional bonding process by metal bumps, it improves flexibility of package because PEB is softer than metal bump and NCF adhesive film keeps mechanical contact between PEB and pad. Elastic deformation and restoration behavior of PEB bump during bonding process are investigated using FEM analysis to calculate bump-to-pad contact area related to electrical contact resistance. Through experiments PEB fabrication process of 50 pm diameter is developed using thermal reflow process and we find optimal bonding conditions and effect of bonding parameters.