Ken,
You didn't say if the board is a multilayer, if so, you may need to
check lay-up construction for metal distribution.  Uneven stackup can be
a major cause of warp.  We are a pcb vendor and we do not regularly
'dewarp' boards.
Anne Ledger
EMDS, Inc.


> -----Original Message-----
> From: Ken Nevius [SMTP:[log in to unmask]]
> Sent: Tuesday, January 19, 1999 4:33 PM
> To:   [log in to unmask]
> Subject:      [TN] Bowed Boards
>
>     We have been seeing boards come off our reflow oven with bow and
> twist
>     that exceeds IPC specs.  Our vendor insists that we are the only
>     customer that complains about this.  We had our reflow oven
> calibrated
>     and it looked fine.  The only thing about the profile that may be
>     suspect is the cooling rate may be a little too fast.  According
> to the
>     vendor, they put all of their boards through a de-warping process.
>      The vendor has tweaked their de-warping process to cool slower in
> an
>     effort to make the problem go away.
>
>     My question is:  This is our first bout with warping, what should
> we be
>     looking at for a cause?  Is it normal for a pc board vendor to
> have to
>     de-warp boards?
>
>
>     Regards,
>
>     Ken Nevius
>     Veeder-Root
>     Altoona,  Pennsylvania
>
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