Comparative study of how additives affect sintered silver microstructure in die-attach applications

Abstract Die attach materials based on silver nanoparticles which sinter at temperatures in the range 200–300 °C are a comparatively new technology. The properties of the sintered structure can be affected by a wide range of additives which can alter the physical and chemical characteristics of the joints. In this study, a commercially available Ag nanoparticle paste has been used as the base, and a range of additives have been added principally to determine the effect of each additive on the sintered microstructure immediately after sintering, and after long term thermal ageing. The additives trialled include Au, Sn, Cu, and Zn. In each case the additive powder was mixed with the original paste and the microstructure after sintering was compared to the microstructure after ageing at 250 °C for 24 h. Another method of introducing an additive into the system is adding it as a mesh, interposed between die and substrate and immersed in the silver paste. Au was added in both this form, and in the form of a powder additive. The mesh results in a thermodynamically stable microstructure up to at least 500 °C. The design takes advantage of solid–solid interdiffusion bonding which results in a die attach assembly with a continuous, non-porous gold-silver interdiffusion layer running all the way from the die to the substrate.