Great discussion...

I was talking with one of our board manufacturing vendors and he told me
that they use 18 x 24 and 21 x 24 for quick turns and 20 x 26; 24 x 24 and
24 x 28 in higher volume production for standard lead times.

I still don't exactly understand why but I can speculate that it may be
related to their having a dual approach to supporting their customers
needs... The normal production higher volume work may travel through the
plant in a different way using separate equipment that can handle the larger
panels and the quick turn work may take a path through their equipment that
is optimized for those sizes and processes not commingling with the higher
volume work... hard to say for sure...

For some unknown reason long before I came here we settled on a standard
assembly panel size of 10 X 12 inches and we have been designing our boards
into them like that for the past 5 years that I have been here... It's not
the most efficient use of a 18 X 24 manufacturing panel to be sure... That's
why I am looking at redesigning the panel configuration to be more cost
effective and still compatible with our assembly floor's capabilities...
Higher yields... lower cost per board.

Our solder paste screening machine has a limited depth of about 9.5 inches
of travel and that limits the number of individual boards I can put on the
assembly panel in either axis. Most of the other equipment, pick and place,
washing, wave solder, axial and radial inserters, test equipment, hand
stuffing second op workstations, etc...can handle larger dimensions. The
screening station in our case is the limiting factor. Having a longer panel
than 12 inches here does me no good.

Some folks are making their panels 8.2 X 11.2 inches and fitting them 'four
up' in an 18 x 24 panel with a .75 inch border around the perimeter and a
.100 inch routed separation between them.

Using V-scoring would gain an extra .050 on each edge of the panels if they
weren't routed. This is quite doable since our assembly panels are always
rectangular and with straight edges. We always orient the boards in our
panels in the same direction so the programming for pick and place is easier
and screening and reflow or wave soldering are consistent from board to
board...

Some vendors want more space between the individual assembly panels on their
manufacturing panel and prefer an inch border and .4 between assembly panels
for their tooling, fixtures, holders and test coupons.

Making sure the panel size we end up with is efficient for ANY vendor we use
is really my goal... and that does take a little research to find out what
limiting factors are common among the vendors.

So far it looks like the 8 X 11 size is pretty close to workable for most
any shop and is fairly efficient use of the manufacturing panels they
have... especially the 18 x 24 size...

Then when we do our assembly panel designs we will have to package them into
the 8 X 11 size (or whatever size we finally settle on) with all the needed
fiducials, tooling holes etc...with clearances for machine holders, rails
and such for our assembly equipment designed into them. Then my challenge
will be to get the most efficient use of the space on our assembly panels...


Thanks for the great comments

Bill Brooks - KG6VVP
PCB Design Engineer, C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
Datron World Communications, Inc.
_______________________________________
San Diego Chapter of the IPC Designers Council
Communications Officer, Web Manager
http://dcchapters.ipc.org/SanDiego/
http://pcbwizards.com

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