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62sn36sn2ag on gold terminations?



62sn36sn2ag on gold terminations? | 12 May, 2003

I have always heard to use solder with 2 percent silver to reduce gold embrittlment. One vendor site said this is a myth.

Does anyone know of a specific document recommending this such as IPC or MIL spec. ???

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62sn36sn2ag on gold terminations? | 12 May, 2003

To the best of my knowledge and experience the 2 % Ag component is not for embrittlement but rather to reduce gold scavenging caused by the propensity for tin to react with the gold. I have seen eutectic tin/lead actually disolve gold wire after a few months at room temperature at slighlty elevated humidity

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62sn36sn2ag on gold terminations? | 13 May, 2003

Your vendor site is totally correct. 2Ag is an excellent solder, but it does nothing to prevent tin and gold from reacting chemically. An earlier poster is correct gold goes into solution in liquid solder very fast, less than a second. Gold and tin form a brittle intermetallic compound that is needle shaped. Since gold is more active than silver, the silver will not do dip in slowing-down that reaction.

It's a good idea to limit gold to less than 3 percent of the solder connection. That's why: * People spent so much time talking about gold thickness in ENIG solderability protection a few years ago. Both IPC-4552 & 2221 give ENIG specifications. * J-STD-001 requires solder dipping of components with gold plated leads.

Search the fine SMT Archives for more.

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