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July 1998

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Subject:
From:
Brad Vanderhoof <[log in to unmask]>
Reply To:
Date:
Fri, 10 Jul 1998 11:08:15 PDT
Content-Type:
text/plain
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There is a world of difference in the quality of laser cut stencils (and
stencils in general).  Smooth walls are preferred.  Some laser stencil
cutters provide smooth walls without electropolishing, others yield so
rough a surface it doesn't help.  Be careful, one prominent stencil vendor
has a habit of charging for electropolishing and not doing it.  Nickel
plating is debatable.  The same low surface tension properties that may
cause paste to release slightly better has a negative impact on paste roll.

Regards,
Brad

-----Original Message-----
From:   Todd Ness [SMTP:[log in to unmask]]
Sent:   Friday, July 10, 1998 2:13 AM
To:     [log in to unmask]
Subject:        [TN] Electropolishing Laser-Cut Stencils

Hi all,

We are currently having problems with a laser-cut stencil that is
electropolished and nickel plated with 9-mil openings. The paste does
not release well from the apertures. We are having to wipe after every
print. The board is fixtured well and we have been using the same
paste for the last two years. We had a different laser-cut stencil in
production from a different manufacturer with the same 9-mil opening,
but this stencil was not electropolised or nickel-plated. With this
stencil, the paste release was excellent and we never had to worry
about wiping.

Does anyone have any input into whether or not laser-cut stencils
should be electropolished and nickel plated? I have heard
contradicting opinions on this subject. One source has said that you
do not want to electropolish laser-cut stencils because the
rough laser walls will give you a better paste release. Whereas,
another source has said that the smooth laser walls will give you a
better paste release.

Also, what benefit does nickel plating give you? Does the paste tend
to roll better with nickel plating? Do you tend to get more or less
paste deposit on the boards with nickel plating? Does it increase the
life of the stencil?

Has anyone using laser stencils seen major differences between
the quality of different stencil manufacturers?

Any input into this subject would be greatly appreciated.

Thanks,
Todd

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