Intermetallic reaction between electroplated indium and silver layers

Reaction of indium (In) and silver (Ag) during the electroplating process of indium over thick silver layer was investigated. It is found that the plated In atoms reacts with Ag to form AgIn2 intermetallic compound at room temperature. Indium is commonly used in electronic industries to bond delicate devices due to its unique ductility and low melting temperature. In this study, copper (Cu) substrates were electroplated with 60µm thick Ag layer, followed by electroplating In layer with thickness of 5µm and 10µm, respectively, at room temperature. To investigate chemical reaction between In and Ag, the microstructure and composition on the surface and cross section of samples were observed using scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX). X-ray diffraction method (XRD) was also employed for phase identification. All of results clearly indicate that indium atoms react with underlying Ag to form AgIn2 during the plating process. After the sample was stored at room temperature in air for one day, AgIn2 grew to 5µm in thickness. With longer storage time, AgIn2 continued to grow until all indium atoms were consumed. The indium layer, thus, disappeared and could barely be detected by XRD.