A few of our components have leads with a silver finish. Will silver cause solder embrittlement? Is removal of silver needed or can it be soldered using 63/37 solder? Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis.
He has vast experience in SMT equipment, materials and processes.
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics.
He is a pioneer in the science of reflow.
Transcript
Phil
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.
Comments
I have experienced gold embrittlement and understand what causes it. We have tin lead solder with silver added. This prevents the leaching of the silver flash on ceramic terminal strips as were used in Tektronix scopes. I can see no issue with silver flashed leads as this was the method used to allow soldering to ceramic terminal strips.
