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March 2002

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Subject:
From:
Roger Stoops <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 14 Mar 2002 08:32:48 -0800
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Food for thought:
IF a board supplier can make an entire board the same size as your panel,
and it meets the warp and twist spec for SMT, then why do they have
difficulty with a board that has multiple images of a smaller board?
I would hazard to think (and it IS a hazard) that the warp and twist spec
would apply to the entire board, whether 1-up or multiple ups.
Ask your board vendor, if they don't want to deliver a panelized board
within spec, how could you trust them to deliver a single board, the same
size, within spec?  And don't accept an argument of "routing between the
panels relieves stress so they warp easily."  What if the single large board
had multiple routes/cutouts?
Either the board design needs to be examined for balance of design, or your
vendor.  Sounds like they may have lost control of their process somewhere.
Sincerely,
Roger M. Stoops,  CID   [log in to unmask]


 -----Original Message-----
From:   Marsico, James [mailto:[log in to unmask]]
Sent:   Thursday, March 14, 2002 7:49 AM
To:     [log in to unmask]
Subject:        [TN] Board Bow and Twist

I think this is a no-brainer, but here goes...  We were delivered boards in
panel form from one of our suppliers.  At Incoming Inspection, the panel was
rejected for excessive bow (>75% for SMT) and returned the supplier.  The
supplier called me and said that even though the panel exceeded the bow
requirement, the individual boards were acceptable.  When I quoted the bow
and twist requirement from IPC-6012, "Panels which contain multiple printed
boards which are assembled on the panel and later separated shall be
assessed in panel form." , he said yes, you measure the individual boards in
the panel.  I need clarification.
Thanks,
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879

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