Grain direction of the cloth can affect warpage.  The cloth relaxes
differently in the grain and machine direction and can result in warpage.

It is not possible to tell from a cross section alone.  You have to know how
the material was made.  If the cloth is asymmetric you can tell the grain
direction of particular board if you know how the grain direction of the
material it was made from.  If the cloth is symmetric, then it is impossible
to tell.

Mike McMaster
RF Product Engineer
Merix Corporation
503-992-4263



> ----------
> From:         davidyeh[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;davidyeh
> Sent:         Wednesday, May 28, 2003 5:54 AM
> To:   [log in to unmask]
> Subject:      [TN] Grain direction in PCB
>
> Hi ,
>
> I am new to the architecture of a PCB and I would like to understand the
> following:
>
> Is there such a term called grain direction in a PCB?
>
> Can anyone advise how to tell the grain direction in the FR4 PCB.
>
> Would the layout of grain direction affect the warpage of board after
> reflow?
>
> Is the grain direction visible via cross section? Is there a means to see
> the grain direction?
>
> Thanks in advance.
>
> Best regards,
> David.
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