Reactivity of no-clean pastes and fluxes for the surface mount technology process—part I: Corrosion behavior of Cu, Sn, and Pb

Abstract

No-clean fluxes allow simplifications in the surface mount technology process, but introduce reliability problems for electronic assemblies during their service life. An electrochemical method is devised to study the anodic reactivity of Sn, Pb, eutectic Sn-Pb solder alloy and Cu in aqueous solutions containing no-clean paste residues obtained during a reflow process. The potential corrosion risk of residues from two different pastes is evaluated, and the corrosion behavior of the different metals assessed. Cu corrodes faster than Sn, Pb, and the solder alloy in presence of the residues, but corrosion starts at higher overvoltages. Pb corrodes at low overvoltage; Sn is prone to oxidation and passivation. The solder alloy has an intermediate behavior between those of the pure metals.