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February 1998

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Date:
Tue, 17 Feb 1998 16:39:36 -0800
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Only up to about 35 or 40 requests so far but it is not a problem.

So there is your opportunity, if you've been thinking of asking me for the
article but did not want to be a bother let those e-mails loose now before I
change my mind. :-)

Brian


>Brian ... thanks for the article !!  Reading the number of requests you've
>gotten reminds me of the time I offered to share a conformal coating
>evaluation study with someone on Technet ... I ended up with about 50
>requests for the report!  Sheila
>
>
>At 12:27 PM 2/17/98 -0800, you wrote:
>>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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>>
>
>
>

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