Re: Another scope 7854


On Fri, 5 May 2017 07:11:08 +0100, you wrote:

I originally thought that but when I ran across the problem, removing the solder revealed that the
entire solder to gold interface was a purple-brown color. I suspect this was a long term effect
whatever flux Tektronix used during assembly.
Using tin-lead solder on gold plating is not a good thing. In space application, component leads are
gold plated to prevent oxidation of the underlying wire and maintain solderability. But the leads
are "degolded" prior to assembly using a solder bath (the gold plating dissolves in the solder). If
you don't degold, you get contact embrittlement because of the gold/tin/lead intermetallics.

Do a google search on degolding - there is a bunch of stuff on there including you tube videos, and
automatic machines to bulk degold.

One of the NASA papers on the subject recommended removing the gold by
dissolving it in tin which is what I ended up doing. It took a few
passes of applying solder and removing it. The gold dissolves in the
tin better at higher temperatures but I had better results at a low
temperature applied for a longer time to avoid damaging the
polysulfone board substrate.

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