The warpage percentage stated in IPC-275 is for the bare board, and
makes no difference as to thru hole or SMT assembly. Depending on the
number of layers and the copper balance, you can reduce the bow. I would
recommend not using ground and power planes unless they were on
opposites of one core material.

> ----------
> From:         Hamilton, Richard -4454
> Sent:         Wednesday, February 18, 1998 6:00 PM
> To:   [log in to unmask]
> Subject:      Re: [TN] PCB warpage
>
> Jim,
>
> I am used to the .01"/inch myself in the TH world. We are just
> beginning
> to get into the SM world and I thought I had seen a much tighter
> tolerance when one is talking about SM. I have ordered the IPC specs,
> but they have not arrived yet. Can you confirm to me that the
> .01"/inch
> is valid in SM also?
>
> Thank you sir.
>
> Richard Hamilton
> Clemar Mfg. / Rain Bird
> [log in to unmask]
>
> > -----Original Message-----
> > From: Jim Mathis [SMTP:[log in to unmask]]
> > Sent: Wednesday, February 18, 1998 2:27 PM
> > To:   [log in to unmask]
> > Subject:      Re: [TN] PCB warpage
> >
> > I spec'd out .01"/inch, also, which used to be the spec.  IPC-275
> > section
> > 5.2.5.2 now specs Bow & Twist in terms of percentages.  If you don't
> > have a
> > copy of IPC-275, let me know and I'll fax you the appropriate pages.
> >
>
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