Liquid Tin Corrosion and Lead Free Wave Soldering Jim Morris Speedline Technologies, Inc., Camdenton, MO Matthew J. O’Keefe, Ph.D., Martin Perez, PhD University of Missouri - Rolla, Rolla, MO Abstract Corrosion of solder pots and solder pot components in wave soldering equipment has been reduced with the introduction of corrosion resistant coatings and improved lead free solder alloys. The latest trends in protecting wave solder machine components from liquid metal corrosion by lead free solder alloys will be presented in order to provide guidelines for evaluating existing equipment as well as for purchasing new systems. New lead free alloys are available that are less corrosive than earlier Sn/Ag and Sn/Cu alloys and can be utilized in older, unprotected equipment for a longer period of time. Cast iron, titanium alloys, and stainless steels coated with titanium nitride and Melonite QPQ are discussed and evaluated. Coatings and materials evaluations are based upon chemical, structural, and visual analysis along with field experience. Additionally, solder pot contamination sources, and tips on how to avoid contamination, are presented. Introduction The transition to lead free wave soldering in North America continues to increase. The European directives, China initiatives, RoHS, and competitive pressures are eliminating tin lead soldering at a fast pace. Lead free is here and wave solder process engineers must understand the process and equipment impacts to succeed in the electronics assembly market. Figure 1 – Unprotected Stainless Steel Background The initial conversion to lead free in mainstream electronic assemblies began in the late 1990’s. Early adopters discovered that the Sn/Cu and Sn/Ag solders caused severe corrosion of the solder pot components. Stainless steels used for soldering equipment at that time would quickly degrade with high tin (Sn) lead free alloys. Figure 1 shows the result of unprotected stainless steel running in Sn/Ag solder for approximately six months. Alternate solder pot alloys and coatings were developed to resist Sn corrosion. Wave solder equipment manufacturers began offering a variety of solutions for new equipment and upgrades for older equipment. Melonite QPQ ® 1 , gray cast iron, and titanium were found to provide good protection 2 for these early alloys and continue to remain popular for today’s equipment. Early Sn/Cu and Sn/Ag solders have been superceded by the Sn-Ag-Cu (SAC) alloys and lead free alloys containing small amounts of nickel. Some of these newer alloys are purported to reduce or eliminate the corrosion of unprotected stainless steel solder pot components. Corrosion Protection Methods Corrosion protections for solder pot components come in two generic types: homogenous materials and coatings. Homogenous materials are materials that naturally resist tin corrosion such as titanium and gray cast iron. Coatings are surface treatments that are applied to the base materials that imparts a level of tin corrosion resistance. Titanium nitride and