On Sep 13, 2004, at 8:18 AM, Denny Esterline wrote:

> It's also interesting to note that many board houses do not use this
> etchant. Some processes use tin plating as an etch resist

http://www.thinktink.com/stack/volumes/voliii/consumbl/etchmix.htm

Is a rather similar etchant based on Sulfuric acid and peroxide, but
uses mysterious "organic catalysts" that they want you to purchase.
(thinktink.com has a bunch of interesting info on PCBs...)

It's worthwhile to assume that commercial board houses can be set up
to use etchants that are neither safe or convenient to an amateur.

BillW

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