From: email@example.com (Bob Wilson)
Subject: Re: Etching!
Date: Sun, 20 Oct 2002 05:31:05 -0000
Organization: Your Organization
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References: <3DB011CC.firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
In article <email@example.com>,
>firstname.lastname@example.org (Tom Bruhns) wrote in message
>> I use basically the same technique as John describes. For small
>> boards, I just float the board on the surface of the FeCl3 solution.
>> Surface tension is enough to hold up several square inches (tens of sq
>> cm) of board, generally. For large boards which don't seem to fit any
>> available etching tray, I'll put little holes in the margins and
>> install nylon screws to hold the board up. If I'm impatient, I'll
>> heat the etchant a bit, but room temperature works fine with patience.
>> The method has an additional advantage of producting very little
>> "undercutting" because the spent etchant seems to accumulate on the
>> little shelf of photoresist as the undercutting starts, and protects
>> it from more etching there. At least, that's my theory; in any event,
>> I can see a distinct difference between a board etched "inverted" like
>> that and one with the etched surface facing up, when looking under a
>That's interesting Tom. I too was trying to find difference between
>the amount of undercutting of vertical panel bubble agitated etching
>and that of horizontal etching in stagnate solution. The one test so
>far showed some improvement, but nothing fantastic though. You can get
>some idea of the degree of undercut with a microscope. I am wondering
>if the undercut from horizontal stagnate etching may be just as good
>as panels etched win a commercial spray etching machine. The etchant
>is not FeCl3, but rather copper ammonia complex type, Cu(NH3)4SO4.
>The problem for me is after etching, the tin metal plating resist can
>overhang the track edges due to etching undercut. Vertical etching
>leaves terrible tin plating overhang and will often form tin slivers
>once broken away. These slivers are a nightmare because they create
>all sorts of invisible electrical shorts. I seems like spray etching
>my be the only cure to etching undercut.
I built a lab-size spray etcher (5 gallon/20 liter heated sump, 12
knife-edge oscillating spray nozzles, 10 Gallon/40 Liter per minute etchant
delivery), and I can tell you that tray-etched PCBs (no matter HOW they are
etched) cannot begin to compare to a spray-etched board, as far as undercut