High-temperature and humidity change the microstructure and degrade the material properties of tin‑silver interconnect material

Abstract

The present work elucidates the microstructural changes and their impact on electrical resistivity and mechanical behavior of Sn-3.5 wt% Ag electronic interconnect material after exposure at high-temperature and relative humidity (85 °C/85%) environment. An in-depth structural observation is performed through electron microscopy e.g., SEM, EBSD and TEM techniques. The microstructural analysis shows that the as-received sample contained sub-micron size ε-Ag3Sn intermetallic compound (IMC) and dendritic structure having a special orientation 〈100〉60° relationship with the matrix grains. However, it is found that after exposing the material at the harsh service environment for 60 days, the morphology, and size of the matrix grains and the ε-Ag3Sn IMC phase are significantly altered. Such microstructural changes impact negatively on their material properties e.g., electrical resistivity, elastic and shear moduli, hardness and creep performance. An assessment between the as-cast and the aged material demonstrated that the degradations in hardness and elastic modulus are approximately 21.8 and 31.7%, respectively. Subsequently, the heat-treated material displays a higher temperature and strain amplitude-dependence damping characteristic as compared to the as-cast solder material.