Interfacial reactions between In and Ag during solid liquid interdiffusion process

Abstract

Ag and In are increasingly being explored as interconnection materials for electronic packaging. However, a deep understanding of their interfacial reaction is still lacking. This study systematically investigated the interfacial reaction between molten In and an Ag substrate at temperatures from 200 °C to 300 °C in a 1–600s time scale. Ag9In4 was the only intermetallic compounds (IMCs) formed during the reflow process. Three types of morphologies were observed during Ag9In4 growth: tiny grains, scalloped grains, and elongated grains. The scalloped grains were regarded as the typical morphology. These scalloped grains are separated by small grains of Ag9In4. A kinetic analysis indicated that the Ag9In4 grew with an inverse cubic dependence on time, following flux driven ripening mechanism. Specifically, ripening dominates growth at first, and grain boundary diffusion dominates growth subsequently. The existence of the small grains prompts Ag9In4 grain growth, because of an increased diffusion area and reduced diffusion distance. This research constitutes the detailed study of morphology evolution, growth kinetics, and growth mechanisms of Ag9In4 grains during the Ag-In solid-liquid interdiffusion process. The results provide insights and guidance for process optimization when using Ag and In as interconnection materials.