A new semester has started at PCC and I am fortunate to have some seriously awesome already professionally employed Electronics Tech’s in my sections. It is so nice to have them. I have come to discover that adjunct teaching in a small (myself + one other adjunct) department is one of the loneliest things to do, pretty much ever. It is a relief to have them, especially in my second section, when I’m tired and my memory and ability to think definitely starts slipping. One of them even caught a could-have-caught-it-with-5-minutes-of-thinking mistake in the PreTest I gave them. Doh! (No Carlyn, gold is not more conductive than copper. You knew that).
We talked about soldering yesterday and one of them asked me about if he needed to do anything special to solder to gold (like you have to do to connect copper to aluminum). Honestly, I had no idea. Seemed reasonable that you might.
So this is where I ran into “gold embrittlement.” When Tin- Lead (PbSn) solder is used to connect to pads or leads that have been protected from oxidation with gold, that gold can mix in with the solder, form crystals and make the solder joint prone to fracture. I haven’t experienced that, to my knowledge, so this was pretty fascinating to me.
- Article about the phenomena from Indium a solder and flux company
- A “famous” classic white paper on the topic of gold embrittlement in PbSn solder (gold needs to be less than 3 to 4% of the weight of the joint)
- A white paper (PDF) on gold embrittlement and lead-free solder (TL;DR – it is less susceptible. They think it is the increased tin content)
- According to IPC (Association Connecting Electronics Industries) Silver embrittlement happens too. (nice electron microscope pictures, it can still happen at less than 3% of weight)
- FORUM: DIY Audio forum topic on soldering to gold plated contacts
- FORUM: Eng-Tips forum topic on soldering to gold
According to the IPC link embrittlement is the wrong word to use, it is more about the formation of crystalline structures. Maybe they are right, because the phrase made Tod (@todbot) think of the gallium invasion of aluminum. I wonder if the phenomena are related?