Characterization of Nonconductive Adhesives for Flip-Chip Interconnection

摘要

For chip-level interconnection,nonconductive adhesive (NCA) is emerging as one of the promising substitutes for solder interconnection because of its inherent fine-pitch capability and environmental friendliness.The NCA interconnect relies on the mechanical connection between the contacts on the chip and corresponding contacts on the substrate enabled by the compressive stress created as the NCA epoxy cures.The degradation mechanism of NCA technology is,however,relatively less well understood compared to solder interconnects in terms of materials requirements for enhanced reliability performance.This study addresses the impact of material systems employed on the reliability of the packages.This involves characterization of NCA pastes in thermomechani-cal,hygroscopic swelling,and moisture diffusion properties.The reliability evaluation was carried out using electroless nickel/gold perimeter bumped test chips with daisy-chained connections.Analysis showed that interfacial delami-nation and open contact were the major failure modes in the NCA package.Pressure cooker test (PCT) performance was improved by using NCA with low-saturated moisture concentration,low coefficient of moisture expansion,and high adhesion.For better performance in the moisture sensitivity test (MST),the key properties required were high shear strength and low moisture diffu-sivity Interestingly,filler content shows opposing behavior in the MST versus the PCT.Thus,optimum filler content must be found.