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November 1998

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 6 Nov 1998 14:25:52 EST
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In a message dated 11/6/98 8:53:56 AM Pacific Standard Time,
[log in to unmask] writes:

<< Hi Technetters,

 I have a curious question to ask, regarding the MPM auto-printer.

 If there is only 1 set of printer, however, has 10 stencils of
 the same kind of openings (Basically all the stencils are the same,
 used for only 1 type of PCB's pattern).

 If 1 of the 10 stencils is being used as reference for teaching, is
 there a requirement to re-teach every single stencil that is loaded
 into the printer to ensure the printing accuracy ?



 Regards,
 Poh>>

Hi there Poh,

If it were a perfect world, I would say no. But things being how they are,  I
would say that there could be a few reasons that you might need to teach every
stencil:

1. Variations in the way the foil is mounted in each frame - The stencil
vendors I've worked with are pretty accurate as far as being consistent and
repeatable when mounting the foils, but that still is pretty much a completely
manual operation... so there's going to be some human induced variation. The
thickness of the epoxy that was applied to bond the mesh to the frame, and the
foil to the mesh, is going to vary between stencils. The foil tension is going
to be a little different between each stencil too, again due to the mostly
manual operation.


2. Variations in the frames themselves - I've always reused many of the frames
for my stencils...it's an easy way to save some money. But having foils in and
out of them over and over again will cause each frame to develop it's own
"personality" over time.

Of course if we're talking about stencils that only have 1206 openings and a
few 50-mil pitch IC's in it, then you might get by teaching one stencil and
using the same parameters for the others. But when dealing with the pitches we
all deal with nowdays, I'd teach every stencil if it were me....heck, it only
takes 10-minutes, if that...

-Steve Gregory-

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