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Lead-free SMT soldering defects<br>- how to prevent them
The change from 63/37 eutectic to lead-free solder need not increase defects provided the new process is understood. This article examines the reflow process and the characteristics of different solders and fluxes, and their effects on common defects like solder slump, solder balling, solder bridging, wetting and dewetting, and voids.
Tin-silver-copper alloys are the primary choice for lead-free SMT assembly, although there are other options available, such as alloys containing bismuth or indium and other elements. However, tin-silver-copper solders, also known as SAC alloys, are by far the most popular, and are preferred by approximately 65% of users (Soldertec 2003).
The lead (Pb)-free SMT process differs from a 63/37 eutectic process in numerous ways. A good understanding of these differences when using SAC alloys, will enable process engineers to bring about the necessary changes to the SMT process to reduce soldering defects, increase lead-free assembly reliability, and maintain production yields.
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