Development of PEB Face-Down Interconnect Process for Wearable Device

Abstract

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, whichcould reduce stress concentration remarkably near bump and chip face by soft polymer bump material with electroconductive metal linepattern and usage of NCF(non-conductive adhesive film) and also lower bonding temperature during facedown interconnect process between flexible substrate and ultrathin 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 is developed using thermal reflow process and spiraltype and spoke type PEB are developed in order to solve the Au cap metal line crack problem due to excessive deformation of PEB. We find optimal bonding conditions and effect of bonding parameters.