Tek and HP used the gold plating *as* the solder mask for
copper etching.
Their process was (approximately):
1) drill plated through holes
2) plate through holes.
3) silkscreen a mask on board that covers everything that
isn't a trace.
4) gold plate board.
5) remove mask.
6) etch board.
7) drill board holes that aren't plated through
8) route outline of board.
-Chuck Harris
Jeff Urban wrote:
...
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This board is obviously copper, but is overplated with gold. As with any board it has connections to the components. Without solder mask the solder will cover all the foil, but it didn't. The only thing that makes sense is that they removed the solder mask after. And they have whose cutouts for connections to things with too much thermal mass, which would throw the whole process off.
