Corrosion Research Of Different Lead Free Wave Solder Pot Materials

Tremendous influence has been worked by the Lead Free in Surface Mount Technology (SMT) and its development on the producing of wave soldering, especially on surface corrosion of stainless steel solder pot in lead-free condition.Solid-state base metal would be dissolved to solder when contact with liquid-state solder, and corrosion would be occurred when over dissolving. The corrosion is restricted by many factors, such as temperature, element consistency, etc. Operating on Sn-Pb solder condition, surface corrosion of stainless steel is not so serious, whereas by the use of lead-free solder, due to the increase of operation temperature and enormous enhance of Sn content in lead-free solder, severe corrosion occurs swiftly on the surface of stainless steel.The most distinct character for the dissolution of stainless steel is the produced of Fe-Sn compound. Operating under the temperature for wave soldering, Fe and Sn can react and create acicular brittle compound whose major element is FeSn₂. The development of compound is not a balanceable process. Variform corrosion morphologies appear on the surface of stainless steel under the influence of solder's fluid factor, lacuna on material's surface and component variation, as well as the dissolution of compound itself and so on. The increase of temperature has great effect on stainless steel's corrosion. Severe corrosion will occurs on the surface of stainless steel rapidly when temperature up to 450℃. The material used for solder pot, particularly for the part with a tight contact with flow solder, should avoid direct use of stainless steel.Sn contained in Sn0.7Cu will diffuse into cast iron equally and react with Fe and then create FeSn₂. At the same time, abundant graphite contained in cast iron could obstruct from invasion of Sn, so that cast iron in still solder has nicer corrosion resistance. Cast iron is a bit of brittle with coarse surface that could be easily affected in flow solder. Considering price predominance and limitation of machining capability, cast iron can be popularized and utilized as pot material.No reaction has been observed between Ti and solder in experimentation and no evident corrosion in sample's surface. The effect from flow solder to Ti is slight as well. The regular service life of Ti solder pot is seven times longer than...