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Can Silver Cause Solder Embrittlement?
Board Talk
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TranscriptPhil And welcome to Board Talk with Jim Hall and Phil Zarrow, The Assembly Brothers, pick and place. We are here to discuss your processing problems, situations, methodologies and all that falls out of the sky at you. Jim, today we have a question from F.A. A few of the components we are using have leads with silver finish. Will silver cause solder embrittlement, like gold? Is removal of silver needed or can it be soldered using SN63 PB37 solder? Interesting, silver embrittlement. I don’t think that I have encountered that but then again I haven’t been everywhere. What is your take on that? Jim Well, I think you called it earlier Phil. One of the common surface finishes applied to printed circuit boards is immersions silver over copper. In that process when you solder to one of those boards that silver dissolves or leaches into the tin-lead solder or the SAC solder, whatever the tin-based solder. You solder to the copper underneath. It is a very good finish, many people use it. Obviously, there is not a thick layer of silver on the pads. One would have to question if there is a possibility. I agree with you Phil, I have never heard of silver embrittlement as you do gold embrittlement. But once again, silver is expensive. I wouldn’t expect manufacturers of components or printed circuit boards to put any more on than they have to. I would like to highlight that, remember we are talking about silver. The silver is dissolving and you are actually soldering to what is underneath. You should understand carefully what is under that silver that you are dissolving off. Is it nickel, which is very common? I hark back to the very early days of resistors capacitors and reflow soldering when we used to get chip capacitors that had pure silver leads. I mean silver connected directly to the electro-layers in the package. Of course, when you started to reflow solder them that silver would dissolve. The problem was that there was nothing underneath to solder under. You got open joints and ceramic chips falling off of the board after soldering. The solution there, which has continued throughout the industry pretty extensively, it to put a nickel base called a barrier layer on top of the base metal on the leads. The cover that will silver. In soldering you dissolve the silver into the tin-based solder forming inter-metallic with what is underneath, in this case nickel, just as you would on virtually all of the components that you buy today. They are actually matte tin over nickel. But the same process, the tin dissolves into the tin-solder and you form the inter-metallic with the nickel underneath. In any case, you should be aware of what is underneath and make sure that the flux you are using is compatible with it. Phil Well good, I think we covered that. If there is such a thing as silver embrittlement, we will hear it from our readersRemember, when you are soldering to a silver finish just be aware and don’t solder like my brother. Jim And don’t solder like my brother. Phil Or you might wind up with silver embrittlement. |
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