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From: firstname.lastname@example.org (Adam Seychell)
Subject: Re: Etching!
Date: 19 Oct 2002 05:28:40 -0700
References: <3DB011CC.email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: 19 Oct 2002 12:28:40 GMT
email@example.com (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.
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