Tips for How to Choose a Reflow Solder
Reflow soldering is a soldering process commonly used on electronics and computers. It employs solder paste comprising alloy powder and flux. Circuitry or other components are attached temporarily to a circuit board, then the assembly is heated, permanently affixing all the components. Reflow soldering is usually a production process, so choosing the correct solder, flux and combination is critical to achieving consistent, high quality results. The selection process is extremely technical.
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Alloy Selection
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Solder is not pure silver; it's a silver alloy. Variants of the silver alloy solder have corresponding physical properties. The alloy has to provide the strength required by your application. Usually of greater importance in the manufacturing process is precise temperature control: it must melt consistently at a temperature that works for your application.
Flux Selection
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Once you've chosen the the correct alloy or range of alloys that will work, flux selection is the next critical step. Understand that fluxes vary dramatically. Familiarize yourself with the five basic categories of flux: R, RMA, RA, NC and WS. Knowing the industry-defined categories will help you find the best choice.
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Process of Elimination
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Chances are, more than one flux will work for your application. However, with production soldering, it's expensive to guess --- especially if you guess more than once. The process of choosing the right reflow solder should first be a process of elimination. Be organized. List the solders you consider and eliminate those that don't have the correct melting point, flux residue or strength.
Special Solders
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In refining your choice, you may choose to substitute another readily available reflow solder with the one you're using, selecting different performance characteristics in small increments. If it's not clear that another ready-made formula will improve your results, be aware of specialty solders. Many manufacturers make custom compounds specifically for your application and create the formula specifically for you, based on your feedback.
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