We have always referred (perhaps wrongly)to an acid trap as a design feature
particularly where a trace adjoins a square or rectangular SMT pad at the
pads center and then abruptly makes a 90 degree bend running parallel with
the pads edge with minimum spacing between the pad and the trace.  This
results in a very small portion of photoresist remaining after outerlayer
developing.  What can happen is that this small area of resist has little in
the way of mechanical bond and becomes a "flap" usually bending itself over
onto the adjacent circuit causing the absence of copper pattern plating and
obviously tin overplate.  The result is a nice open trace after etch.  I'm
not familiar with any other nomenclature even though the name "acid trap"
doesn't seem to fit either.

Mike Bailey
Director of Engineering
McCurdy Circuits Inc.
4900 E. Hunter Ave.
Anaheim, CA  92870
Phone: 714 507-4900 Ext 253
FAX: 714 507-4911
e-mail: [log in to unmask] <mailto:[log in to unmask]>


-----Original Message-----
From: Takach, Lou J [mailto:[log in to unmask]]
Sent: Monday, May 08, 2000 9:35 AM
To: [log in to unmask]
Subject: [TN] What is an acid trap?


I have a question that you can hopefully help me with. Recently, our
manufacturing plant reviewed one of our designs and identified several areas
that contained acid trap situations. Can you give me a good definition as to
what an acid trap is and what damage it could cause to a board?  After I
reviewed the design, I did notice quite a few areas that might be a problem.
Before I fixed anything, I sent the files to the board fabricator that does
our production work. They performed their normal checks and found no
problems. They then reduced the criteria that they search on and again,
found no problems. I need to respond to not only our manufacturing people
but also to the engineers involved with this design as well as management.
Any help would be appreciated.

Thanks...

Lou Takach
Union Switch & Signal
1000 Technology Drive
Pittsburgh, PA 15219
412-688-2574
[log in to unmask]

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