Acting capability of flux for Pb-free interconnection in electronics assembly

The components and characteristics of flux used for Pb-free interconnection are discussed. Applying physical chemistry principles, the decisive factors, activation capability and limit of the flux's activity are analyzed. The results show that special flux must be used in Pb-free interconnections, and acting capability of flux mainly depends on the selected activator, and the built-up activator is an effective way to elevate activity. Flux with high activity can significantly enhance sigmas-f and reduce sigmal-f, but it can not reduce sigmas-l effectively. It is a basic reason why activity is difficult to exert. Reducing the fast growth of inter-metallic compound (IMC) at the interface is a vital measure to improve acting capability of flux.