Study on high temperature bonding reliability of sintered nano-silver joint on bare copper plate

Abstract

Nano-silver paste has become an alternative lead-free (Pb-free) die attach material for microelectronic packaging, compared to traditional solders and adhesive films, due to its higher thermal and electrical conductivity, higher temperature operation and higher heat dissipation. In this study, the reliable joints of sintered nano-silver paste on bare copper plate with large-area dummy chips were introduced and thermally aged at 150°C, 180°C, or even higher than 250°C in air or in a coarse vacuum environment. The bonding strength and interfacial reaction were investigated. The results showed, after aging specimens at 150°C for 960h in air or at 250°C for 960h in a coarse vacuum, the interfaces between the sintered nano-silver and bare copper still consisted of simple inter-diffusion bands and with almost no change in bonding strength. However, the bonding strength sharply decreased to 50% after aging at 180°C for 72h in air and it decreased to 20% after aging at 250°C for 72h in air. The decrease in bonding strength was mainly attributed to the oxidation of copper at relative elevated temperature in this work.