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.