Lead-Free Solder Joint Voiding: The Causes are Starting to Surface

Much research work has been conducted into the cause of voiding and Henkel has studied in-depth the materials relationship to voiding. When using SAC alloys, in order to achieve the desired wetting and ultimate interconnection, the fluxes in the paste formulations have to operate at higher temperatures than those of their SnPb counterparts. Not only do the fluxes work harder, the SAC alloys also have a higher surface tension than tin-lead, increasing the possibility that unwanted volatiles are trapped within the molten solder. These volatiles cannot escape as easily, and voids are created when these compounds remain in the body of the solder once the material is solidified. Previously published works by our company outline the benefits of utilizing a low voiding solder paste formulation to alleviate both mechanical and electrical issues associated with Pbfree solder joint void formation. ( http://www.smtmag.com/whitepapers/556) Using a low voiding solder paste formulation such as one of Henkel’s Multicore® LF series materials serves to significantly reduce the incidence of voiding, but there may also be other factors that should be considered for void reduction and improved long-term reliability.