Minimizing flux spatter during lead‐free reflow assembly

Abstract

PurposeThe leaching of lead from electronic components in landfills to ground water is harmful to health and to the environment. Increasing concern over the use of lead in electronics manufacturing has led to legislation to restrict its use as a joining material. Consequently, significant recent research efforts have been geared to identification of suitable lead‐free solder pastes. Typically, lead‐free solder pastes contain a very active flux in an effort to improve wetting. These aggressive fluxes have the tendency to explode (or burst) and create flux spatter, causing many process problems with sensitive electronic components. The purpose of this paper is to propose solution procedures to minimize/eliminate these flux spatters, particularly, on gold fingers in memory modules when lead‐free solder pastes are used.Design/methodology/approachFour no‐clean, lead‐free Sn‐Ag‐Cu (SAC) alloy‐based solder pastes consisting of four different flux systems from three different vendors were evaluated. Two types of reflow profiles (linear and ramp‐soak‐ramp) were also evaluated. Experiments were also conducted to optimise the soak temperature and soak time to determine a broader process window for lead‐free volume production with minimal flux spatter on the contact fingers of memory modules. In order to validate our findings the recommended profile and paste was adopted in production. Additional experiments on a board with a different surface finish were also carried out to validate the recommendations.FindingsFlux spatter can be reduced/eliminated through proper selection of flux chemistry and reflow profile optimisation. The experimental study conducted indicates there is a reduction in the occurrence of flux spatter when a ramp‐soak‐ramp profile is used with lead‐free solder pastes.Originality/valueDemonstrates that flux spatter can be reduced/eliminated by carefully choosing a soak profile and appropriate flux chemistry.