Re: Another scope 7854

Craig Sawyers <c.sawyers@...>
 

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.


------------------------------------
Posted by: David <@DWH>
------------------------------------
We looked at a number of esoteric board substrates whose CTE was matched to typical gullwing IC's
and surface mount passives for strain-free with temperature cycling. I forget what we chose
eventually - but it was out of production (the certified board house had hoarded a load of the
stuff).

Plus there was a whole load of other requirements - no solder resist, no silk screen. And no traces
on the top and bottom - everything had to be in an inner layer other than ground planes. We pretty
quickly ended up with ten layers.

Craig

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