Hi Vladimir,
Did you check?

   - PCB laminates Tg? the same from both vendors?
   - Same thickness?
   - Do the new panel have copper balance on all layers on the panel frame?
   - Do the temp. profile is comply to the laminate materials (Lead free
   profile?).

Reuven

On Thu, Sep 29, 2011 at 6:49 PM, Vladimir Igoshev. PhD <
[log in to unmask]> wrote:

> Hi TechNetters,
>
> I have a question for board gurus, as I'm almost lost.
>
> Here is a story. A panel of four simple 4 layers FR4 twists after
> going through the first side re-flow and flatten out after the second
> side is re-flowed.   It does the same thing with and without the
> components placed.
>
> The panels are from  new vendor and the old ones had never exhibited
> the problem. What confused me is that both boards (from both of the
> vendors) were built identically: dielectric layers and  Cu
> layers are look identical thickness- wise.
>
> There are no signs of resin recession or delamination in
> cross-sections which could have pointed out at incomplete curing.
>
> Glass bundles look also identical.
>
> What else it could be?
>
> Any suggestions are deeply appreciated.
> --
> Best regards,
>
> Vladimir Igoshev. PhD                          mailto:
> [log in to unmask]
>
> SENTEC Testing Laboratory Inc.
> 11 Canadian Road, Unit 7.
> Scarborough, ON M1R 5G1
> Tel: (416) 899-1882
> Fax: (905) 882-8812
> www.sentec.ca
>
>
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-- 

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*Reuven Rokah*

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