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| From [log in to unmask] Sat Apr 27 15: |
07:19 1996 |
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We assemble some pretty large boards that have 20 mil pitch parts as far as
28 inches apart on the diagonal. On a number of occasions we've had to
order 'shrunk' stencils to match the boards. I've yet to run across a
board that was 'stretched'.
Your stencil vendor's photoplotter accuracy becomes rather critical for
very large stencils. We measure the actual artwork on the boards and give
the vendor a scale factor for each axis. Typically the scale factor will
be slightly different in each axis.
Cheers,
Doug Ondricek
Convex Computer Corporation
> From: Kelly Kovalovsky, PCB Quality Engineering
> ~ EMail:[log in to unmask]
> Subject: PCB vs. Paste Stencil Comp
> We have a fairly large circuit board that we are assembling. The card
> has fine pitch SMT at extreme ends. We have noticed a mismatch between
> the solder paste stencil and the printed circuit board. The circuit
> board features are actually closer together than the stencil.
>
> My question to any card assembly site is whether it is common practice
> to compensate a solder paste stencil for shrinkage of a PCB?
>
> IBM Microelectronics Division
> 6800 IBM Drive MG12/251
> Charlotte, NC 28262-8563
>
>
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