Doug,
You could attach a process tag that goes with the board and have the
inspectors and testers stamp that instead. I'm sure you could make your
manufacturing processes accommodate the change and still maintain
traceability. The product at the customer's site does not need the stamps
on the PCB, you just need to maintain traceability during your manufacturing
process.
Just one low-tech option I'm sure.
Dan
-Original Message-
From: POWELL, DOUG [mailto:doug.pow...@aei.com]
Sent: Friday, December 06, 2002 6:03 PM
To: EMC-PSTC (E-mail)
Subject: PCBA Inspection Stamps
Hello group,
I have a request for information on stamping methods of PCBAs. I would
normally post this question on one of the discussion forums for PCB design,
but this question really does pertain to product safety. But first, please
indulge me while I provide a little background information...
My company uses a very large number of PCB assemblies with wide variety of
technologies. Many of these boards have safety considerations and receive
routine hipot testing during manufacture. As is normally the case, in-house
and outsource assembly of the boards requires various kinds of inspection
and test with stamps for validation. Traditionally these are rubber stamps
or some form of an adhesive label with printing. Many of our boards have
high voltage separation from SELV circuits and as it turns out the most
convenient place to put a stamp is in a safety keepout zone. There have
been a number of hipot failures that track right through this stamp. In our
standard practices manual, we specify the use of only white epoxy based
inks, but some of these are conductive as well. In addition, with the ever
shrinking geometries of high density boards, placing a nonconductive stamp
on a low voltage circuit interferes by insulating test points for bed of
nails testing. Since inspection marks are usually placed by hand, the
faults we see are fairly random. So, on the one hand conductive inks are
bad and on the other hand nonconductive inks are bad.
In an effort to solve this problem, we've considered providing a
silk-screened area of the board that is safe to stamp, but real estate is
now at a premium and solder-side silk costs on average about 10% more.
Plus, it won't be long until computerized component ID and location
eliminates the need for silk-screen entirely.
My question is this: Has anyone discovered a technology or process of any
sort, for marking of ultra-high density or high voltage PCBAs and is easy to
implement in most board houses? I have to think that with all the
technological advances the old rubber stamp or adhesive label could be
replaced somehow. Who knows, maybe some form of UV identification?
I am very interested to hear any success stories that you may have.
Best regards to all,
-doug
Douglas E. Powell
Compliance Engineer
Advanced Energy Industries, Inc.
Fort Collins, CO 80535 USA
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