Interfacial reaction and dissolution behavior of Cu substrate in molten Sn-3.8Ag-0.7Cu-nano Mo composite solder

Abstract

In electronic packaging, solder alloy is used to connect the electronic devices on the copper pad to switch on the functionality of those devices. When solid copper comes in contact with a liquid solder alloy, reaction takes place and intermetallic compound (IMC) layer forms at the solid-liquid interface. To reduce the diffusion of the substrate, the major issue is to slow down the interfacial reactions between the solder and the substrate metallization. The diffusion rate depends to a large extent on the elemental compositions of the solder and the solid metal. In this study, Cu wire having a diameter 250 µm is immersed in the liquid composite solder at 250ºC up to 15 min. Composite solder were prepared by adding various amount of nano Mo into the Sn-3.8Ag-0.7Cu (SAC) solder paste. Generally the dissolution rate increases with increasing time but decreases with increasing the nano Mo content in the SAC solder. The IMC thickness increases with increasing the reaction time but nano Mo can hinder the growth of IMC layer. As a result, nano Mo is effective for the SAC solder to reduce the diffusion of copper substrate.