Dale:

Your basic assumption may be incorrect.  The openings on a soldermask screen
are normally less than 0.01 inch (closer to 0.005 inch), and the unused ink
has never contacted the board's surface.  Other methods used to apply solder
mask (curtain coat and spray) won't pick up metallic debris.  What you might
be seeing is plating overhang broken from the circuits during the screening
operation.  Another possibility is poor cleaning before mask.

IMO, as long as the particles do not reduce the spacing between circuits
below minimum requirements you do not have a "real" problem.  (Don't like it
either, but how does one reject without a specification violation) However,
you do have a process indicator.  You should pursue the root cause of the
problem.  Poor etching control or poor cleaning could result in other
problems with your boards.  It might also be beneficial to understand why
the suppliers are passing the product and what they use for reject criteria.

Don Vischulis

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dale Ritzen
Sent: Tuesday, December 10, 2002 1:52 PM
To: [log in to unmask]
Subject: [TN] Metal Debris in Solder Resist


Since IPC-A-600 doesn't have much to say about this...

We recently started seeing quite a lot of metallic debris encapsulated in
solder resist from several of our board suppliers. These bare boards are to
be used as a class 3 SMT/PTH platform. There are few references to this in
any standard I have read (including IPC-A-610, sect. 7.2), so I'd like some
feedback on what everyone else is seeing these days and on what they
believe the problem to be (or if they don't believe it to BE a problem).

My take on it is that some board houses may be taking short cuts or saving
money by not using fresh solder resist as often as needed, thus building up
the amount of debris left over from each previous board that has been
coated and leaving it on the following boards. Filtering the resist to
remove this debris before using it again would be helpful, if workable. As
the end user of this I find it bothersome (even though it IS encapsulated
by the resist) as it indicates to me that the supplier may be trying to cut
corners in the current economic climate.

Okay, so is this a real problem or is it a "who cares" issue? On a board
that is to be used as a class 3 platform, it seems to me that this IS an
issue, especially in the rising incidents of debris seen in the resist.

I have pictures of what I'm talking about. If you'd like to see them send
email and will forward them to you for review. Thanks!

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