Hi Judy:
        One of the many causes is copper unbalance of the PWB, in other words the copper mass is greater towards one side of the board than the other. Another one may be uneven heating and cooling of the board while it is not being supported. This subject has been discussed on this forum plenty. I suggest that besides the responses that you are going to  get to also look in the archives.
        Good Luck
        Ramon

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Judy Brown
Sent: Friday, February 04, 2005 1:45 PM
To: [log in to unmask]
Subject: [TN] Warp & Twist


I know I saw what I need somewhere, but I can't remember the document. I need the causes for PCB warp and twist. 

Judy Rae Brown
Quality Assurance Manager
EXPRESS MANUFACTURING, INC.
Electronic Manufacturing Services 
3519 West Warner Avenue 
Santa Ana, CA 92704 
714.979.2228 - Tel 
714.556.0575 - Fax 
Email: [log in to unmask] 
Website: <http://www.eminc.com/>


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