Lou -

The most effective method for labeling PWBs is to silk screen the
nomenclature with a permanent ink prior to assembly. A properly made screen
and skilled operator precludes likelihood of error, and the ink is extremely
durable against mechanical and chemical challenges.

Another option is to copper etch the information onto the bare board,
presuming there is no conflict with functional circuitry. Again, this is a
very durable method.

You might consider having the nomenclature installed as a negative image in
the solder mask, providing (of course) no circuitry is exposed. This is quite
permanent and also foolproof but requires available real-estate.

If the PWB is a multilayer you could consider having the information etched
into one of the inner layers that are immediately facing an outer layer. The
nomenclature could appear as a copper etching in a relieved area of an inner
layer so that it is visible to the outer layer (layers are often identified
in this way, so that proper sequencing is easy to validate from the outside).
Again, adequate real-estate is required.

Labels are available in a variety of materials, ranging from paper to foil to
Kevlar, with a like-variety of adhesion promoters. I personally dislike
labels as they become an additional step to manage and, should they fail to
stick, become a floating liability within the assembly.

Laser-etching is another option but cost & effect may make it unworthy of
consideration.

We usually reserve the rubber stamping of PWBs to those requiring
serialization. Rubber stamps can be messy and, typically, the more robust the
ink the more problematic the application (ink drying / frequent stamp
cleaning can be a major problem). Rubber stamping is also the least
consistent in appearance of all options.

Cheers!

Bob Lazzara
Circuit Connect, Inc.
TEL:    (800) 560-9457
FAX:    (888) 453-0520
WEB:    www.CircuitConnectInc.com


 I have a customer who has been calling for printing of board numbers, revs,
serial numbers using epoxy ink.  This operation is time consuming, messy,
prone to human error.  We've been talking about using computer-printed paper
labels instead of epoxy ink.  The environment these boards go into is not
particularly benign.  Some are used in train cars.  They get an acrylic
conformal coating.

Has anyone had experience in the matter of label durability?  Any test
methods to suggest?  Thanks for any comments.

Lou Hart
412-858-6184
Compunetix

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