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SAC vs. Sn/Ag for Solar Soldering

As a discussion point (read "please feel free to disagree – that's what the comments section is for"), 96.5%Sn/3.5%Ag is NOT the most well suited pb-free alloy for tabbing.  I know not everyone agrees, as evidenced by the amount of Sn/Ag that is requested, compared to Sn/Ag/Cu.  Our industry uses Sn/Ag because it is programmed to, but let's examine why you should consider 96.5%Sn/3%Ag/0.5%Cu (SAC305) instead.






1) Melting Point



The melting point of SAC 305 is 217ºC, compared to Sn/Ag at 221ºC.  Why subject your solar assembly to more heat than necessary?  This could be worth it for mechanical advantages, but are there any?



2) Reliability Data



Since before the Pb-Free craze started, information was collected on certain Pb-free alternatives, using Sn/Pb as a reference.  There is simply more data available for Sn/Ag/Cu.  You can find this information @  Click Here




3) Strength and Raw Materials Cost



In addition to slightly higher tensile and yield strength, using an alloy with a small amount of Cu improves wetting – which in turn improves solder joint strength.  The electronics industry has learned the benefits of Sn/Ag/Cu, it is time for the solar industry to catch up.