I did a board with 3.5/3.5 trace/space that takes up most of a 12x18
manufacturing panel. It costs a LOT, though.
It's a matter of economics, the more material they have to scrap to deliver
a good board, the more you are going to pay. The further you keep your
lines away from the pads, the less dropout you are going to have after etch.
--
George Patrick
Tektronix, Inc.
Central Engineering, PCB Design Group
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
Phone: 503-627-5272 Fax: 503-627-5587
http://www.tektronix.com http://www.pcb-designer.com
It's my opinion, not Tektronix'
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Chris
Ball
Sent: Thursday, October 28, 2004 12:36
To: [log in to unmask]
Subject: Re: [DC] Recommended oversize and tol. reg.
Hi Bill-
Thanks for the quick response. I follow that the further from center, the
bigger the registration tolerance. I didn't realize boardshops were working
reduced panels for tighter registration though. We have 6/6
(0.15MM/0.15MM) boards being cranked out on 18x24 (457.2mm x 609.6mm)
panels, but with 12mil (0.3MM) vias. Not sure whether or not they stack the
boards for drilling at all. We typically assemble 284x208MM (convert to
imperial your own self) arrays, which yields 4 per panel and doesn't cheat
anyone on the working edges around the panel, and also doesn't waste any
space. How many boards per array depends on the size of the board, and
occasionally we use a different config to best accommodate the board size.
Hard for me to think out of the box these days, been high-volume / low-cost
oriented for too many years.
Best Regards,
-Chris (CID hartha)
"Brooks,Bill"
<[log in to unmask]> To:
"[log in to unmask]"
<[log in to unmask]>
10/28/2004 03:00 PM cc:
Subject: RE:
[DC] Recommended oversize and tol.
reg.
Hi Chris,
The tolerances are fairly linear inch per inch (or 25.4mm per 25.4mm for
those of you who don't still have the inches to millimeter issues)...
Manufacturers typically will try to divide the tolerances from the center
of
the panel outward...effectively reducing the error across the panel evenly
and splitting the tolerance variations in half. You may have noticed they
use tooling pins in slots to register the layers in the presses to allow
the
material to expand or contract along radials that pass through the center
axis of the panel.
Holding plus or minus .002 at the center of a panel is much easier than
maintaining it at the far edge of the panel... there is an accumulation of
tolerances over the larger surface... the expansion and contraction of the
materials or their shifting in the tooling is in ppm (or parts per
million),
there is also 'runout' (or slop in the meshing of the gears) in the
drilling
machines that accumulate error, and tooling hole tolerances resulting in
much more variation at the edges of the panel rather than in the center of
the panel...
When I did my 5/5 boards they only would do them one at a time, no stack
drilling or multi board panels and creating a large panel was out of the
question. Largest panel area they could accommodate was about 6x6 inches.
That was also due to the small 8 mil vias I had in that design. There may
be
some shops that can hold the 5/5 over a much larger area than the vendor I
was using but that's really why we need to talk with them and see what
their
processes can handle. Registration of the boards in a multi board panel
gets
worse at the outer edges of the panel the larger the panel size is. The
step
and repeat process is limited in size by their ability to control those
variations at the panel edges.
Best regards,
Bill Brooks - KG6VVP
PCB Design Engineer , C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
http://www.dtwc.com
http://pcbwizards.com
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Thursday, October 28, 2004 11:31 AM
To: (Designers Council Forum); Brooks,Bill
Subject: Re: [DC] Recommended oversize and tol. reg.
Hi Bill-
One question regarding that response:
<snip>
... Another thing to think about is the size of the panel... The
tolerances are much harder to control over a larger area... so smaller
boards would not have as much trouble as a large multiboard assembly panel.
</snip>
Is that really a factor typically? I would expect that even if I did a
small board and didn't have it arrayed out into an assembly panel, the
boardshop would step and repeat the pattern as best fit their usual 18"x24"
(or whatever) panel. Unless the order is for less boards than would fill a
panel, anyway. So... I'd think the size of the board wouldn't normally be a
factor in the manufacturing tolerance.
Best Regards,
-Chris
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