Investigation of mechanical and microstructural properties of a new, corrosion resistant gold-palladium coated copper bond wire

Abstract

In this study we present a newly developed gold-palladium coated copper (EX1R) wire with focus on automotive industry. By using an advanced material composition, halide induced interface corrosion and also sulphur induced pitting corrosion can be prevented sucessfully. Therefore the copper base material was alloyed with further elements to systematically adjust the intermetallics formed at the interface to the pad metallization and to define the microstructure of the copper base material. To show the improved reliability, in a first step three copper bond wires(bare copper wire; palladium coated copperwire (APC) and the new EX1R wire) were bonded to a silicon die with aluminum metallization and a nickel-palladium-gold plated lead frame and encapsulated with chlorine containing mold compound. In a second step, these packages were stressed using a highly accelerated stress test (HAST) and the degradations were analyzed using scanning electron microscopy (SEM). To further compare the new bond wire type with conventional bond wire materials a microstructural analysis of the grain structure using electron backscatter diffraction (EBSD) was carried out on the three copper sample wires. Additionally, the mechanical properties of the samples were investigated by tensile and nanoindentation experiments with the objective to predict interactions between the plastic deformation behavior and chip damage risks during the bond process. The results show that the newly developed gold-palladium coated copper wire shows a much higher reliability compared to the standard wire materials. Furthermore it could be shown that plastic deformation behavior of the new wire type is very similar to that of conventional palladium coated copper wires.