Controlling porosity during transient liquid phase bonding for high-temperature soldering processes

Exploiting the growth rate dependency of intermetallic compounds (IMCs) on the substrate composition, the possibility of controlling porosity during transient liquid phase (TLP) bonding via a composition gradient is investigated. A Cu substrate with a variable Ni concentration was prepared through selective electroplating and subsequent heat treatment. When this substrate reacted with a molten Sn-rich alloy, there was a non-uniform growth of the Cu 6 Sn 5 IMC. It is proposed that by tailoring the direction of the composition gradient in the substrate, the IMC growth rate can be controlled in such a way as to progressively move the solid-liquid front to redistribute any porosity away from the central region of the joint and thereby improve reliability.