Are you seeing bow and twist at incoming inspection or during assembly
processing?

I rarely see PWB's that don't meet the bow and twist spec at incoming. If
you have bow and twist at incoming, check the metal distribution and the
layer stack up of the design. If it is not balanced, this can result in bow
and twist. An improper cooling profile during lamination can also result in
bow and twist.

During assembly, not allowing for thermal expansion of PWB during reflow and
wave soldering - i.e. conveyors too tight, pallets/fixtures without
expansion clearance, etc. can cause problems.

Hope this helps - John Berg

> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Wednesday, April 04, 2001 10:02 AM
> To:   [log in to unmask]
> Subject:      [TN] BOW AND TWIST
>
> Hello fellow Technetters
>
> I would like to know if anyone has had problem with bow and twist on
> .062 thick boards.
> what is the main cause of bow and twist.
> Is this problem more related to bare board fab or component assembly?
> What was the solution to keep the boards within the IPC specs?
>
> Thanks in advance
> Carl.
> Ectronics
>
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