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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