SAC vs. Sn/Ag for Solar Soldering

Half of the world is still "in the dark" about which alloy to use.

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

Comments for SAC vs. Sn/Ag for Solar Soldering

Friday, August 7, 2009 by Chandrasekhar B:: I agree with you on the 5 degrees C lower melting point and more strenght but the finish with more Sn and softness are the major reasons why Industry is preferring Sn/Ag than SAC305 and also breakage or microcracks are more due to harder material like SAC305.
Monday, August 10, 2009 by Jim H.:: While I agree with your explaination of why the industry percieves that Sn/Ag is the go to Pb-free alloy, it should also be mentioned that leading material manufactures offer softer base material (which contributes far more to the overall ridgidity of the ribbon). Regarding surface finish, newer fluxes are better suited to resist oxidation so the finished product should look the same whether you are using Sn/Ag or SAC 305. The tabbing ribbon world is rapidly evolving.
Friday, August 14, 2009 by DIYSolarPanels:: I dunno, Im indifferent to both sides.

Jim Hisert