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 @ www.NIST.gov. 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.
~Jim