Comparison of SLICF with C4 for flip chip bonding with Au, Cu, Pd and Ag studs with SAC solder

Abstract

Flip Chip (FC) interconnects for 3D, 2.5D and wafer level packaging (WLP) are fast becoming a common package for high performance applications. One of key challenges identify in assembly lie in the fine pitch of FC interconnect to the substrate. This paper looks into an instantaneous fluxless bonding techniques of solid liquid interdiffusion by compressive force (SLICF) to form FC joints of Au, Cu, Pd coated Cu (Pd-Cu) and Ag with lead free SnAgCu (SAC) solder. The bumped chip with SAC solder bumps is then FC bonded onto the Au, Cu, Pd-Cu and Ag studs with macroscopic and microscopic analysis using Optical and Scanning Electron Microscope (SEM) respectively. Electron Dispersive X-ray (EDX) is performed to identify the intermetallics with its joint integrity assessed. Poor interconnect observed for Cu and Pd-Cu studs with plasma cleaning. Both Au and Ag demonstrated to be a good candidate to enable WLP interconnect for production for fine pitch FC applications. Ag provides a good alternative to Au for low cost flip chip technology as Ag provides a lower intermetallic growth rate than Au. Further process optimization is needed to enhance the reliability.