Shahed

Because your board is clean, the silver is exposed to the atmosphere.
There are trace amounts of sulfur dioxide and hydrogen sulfide in the
air, derived mostly from burning fossil fuels, but also from volcanic
activity. Silver has an affinity for sulfur and forms silver sulfide,
which is the brownish film you are seeing. Electrically, its presence
will be perfectly benign: it is only cosmetically that it is
disagreeable.

There is no way of preventing it, but its onset may be delayed but,
frankly, I don't recommend it because it means using products which may
degrade the electrical performance, just to gain a few month's
brilliance. If it is really a problem, a clear acrylic conformal coating
is about all you can do.

Brian

Safavi-Bayat Shahed wrote:
>
> Hi everyone,
> We recently had a board fabricated with silver finish.
> After it came back from assembly house the exposed silver finish is been
> tarnish(color changed to brown)during assembly.
> Does any one here has seen this before? The assembly done manually and the
> tarnishing
> happened after they washed the board.
> I appreciate any comment on this.
>
> Thank You
>
> Shahed
>
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