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Date: | Wed, 26 Apr 95 07:29:03 |
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Well Steve I agree with you. We should not have any snap off but snap
off should be used to setup the GSP. You ask how? I'm glad you asked. Use of a
feeler gauge or some other known thickness material and raise the table until
resistance is felt. Remove gauge and raise the table by X amount. X amount is
the thickness of the gauge used. Possible defects if a snap off is used with a
stencil;solder paste peaks,bad solder paste definition and inconsistent
printing.
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Subject: Solder Paste Printing "Snap-off".......
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Subject: Solder Paste Printing "Snap-off".......
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Good day!
First I would like to express my thanks for the inputs I have received
in response to several of my requests in the past. They have all been very
helpful in resolving the issues that I needed help on, or when I needed
"another voice" to echo my position on certain issues. I think we all get
busy and sometimes neglect to acknowledge the efforts of others.
So now that I've finished "kissing-up"...<GRIN ;^D> I'm wondering if I
could solicit for some more opinions....It has to do with stencil set-up.
We're refining and detailing our ISO 3rd-level procedure for the Screen
Printer. A few of us seem to be at "loggerheads" on the issue of stencil
"Snap-off".....
* One side says that when dealing with "fine pitch", using snap-off is the
best way to ensure that you'll get enough paste through the stencil and
on to the PCB.....
* The other side feels that snap-off is a hold-over from the days of
printing solder paste through a screen, and also used to "band-aid" a
problem with the design and/or the workmanship of the stencil...that as
long as the apertures are designed within the guidelines for aspect
ratio of 1.5-2 times the thickness, sidewall quality is good, and the
correct mesh paste is being used, there should be no reason at all for
"snap-off".....
We want to write the kind of 3rd-level procedures that spell out possible
problems that could be encountered during production, so that operators
will "raise the flag" when they run across situations that may have an
affect on the yield of the process, rather than trying to "make something
work" when it isn't right to begin with.....
Thanks in advance!!
.---. .----------- *
/ \ __ / ------ *
/ / \(..)/ ----- *
Steve Gregory
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[log in to unmask]
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Pragmatech Incorporated
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101 Nicholson Lane
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San Jose, California 95134
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Phone: (408) 943-1151
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Fax : (408) 943-1461
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