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February 1998

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Date:
Tue, 17 Feb 1998 12:27:56 -0800
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Mark,

This is exactly what the article I have been referring to discusses. Did you
need a copy as well? If you did I need your fax number.

Technetters,

I am receiving a lot of requests for the PCB Warpage article so it is taking
some time to get to all of you. Please help me to ensure that I do not miss
anyone. If you do not receive the article within 2 days of your request
please remind me by e-mail. Thank you for your patience.

Sincerely,

Brian Stumm
ETS




>Another possible cause for this type of defect can be attributed to your PCB
>suppliers method of curing the Soldermask. If PCB's are cured vertically
>then it is extremely important that the support during the thermal cure does
>not allow the boards to sag. As the TG temperature of FR4 laminate (135
>degC)  in PCB construction is usually below that of the soldermask
>cure.(Normally 150 deg C)
>
>This would then allow the prepreg to assume the shape of the sag and once
>cooled will retain this bow. We have overcome this issue and if you need
>further details please contact me.
>
>I hope this is of some help.
>
>Mark Gillan
>
>Process Engineer
>Prestwick Circuits
>Scotland
>
>
> ----------
>From: ririzarr
>To: TechNet
>Subject: Re: [TN] PCB warpage
>Date: 17 February 1998 10:04
>
>This is due to thermal stresses in the PCB sometimes when they pass the
>oven they become more "soft" and they warp. Why don't you try some
>stiffeners to make the PCB strong enough to withstand the higher
>temperatures?
>Regards,
>Rub?n E. Irizarry-Guzm?n
>Operations Engineer
>
>
>
>
>[log in to unmask] on 02/16/98 04:52:39 PM
>
>Please respond to [log in to unmask]; Please respond to [log in to unmask]
>
>To:   [log in to unmask]
>cc:    (bcc: Ruben Irizarry)
>Subject:  [TN] PCB warpage
>
>
>
>
>What causes PCBs to warp?  How can we prevent this from happening?
>(Thanks to all responses in advance!)
>
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