Well...The first answer is that the construction appears to be
     a symmetrical build. (Balanced from the theoretical center outwards)
     Next question....Are the circuitry layers also balanced????
     (ie, signals and planes)
     Was the warpage bowed or twisted?? 
     (Possible cross plied problem???)
     
     Next variable could also be related to lam cycle ROR (Rate of Rise)
     and ROCD (Rate of Cooldown). If either is rapid and not tightly 
     controlled you could easily produce a warpage condition.
     
     Another could be non-parallel lamination fixturing/press platens.
     
     
     Sorry....a lot of parameters can cause (contribute) to that condition.
     
        Hadco Printed Circuits
     Tech Center Two / Watsonville                
     
     
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     Dave Hoover              (408) 728-6677 
     Senior Process Engineer  (408) 728-1728 Fax 
     [log in to unmask]
     
     


______________________________ Reply Separator _________________________________
Subject: warping
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    10/18/95 9:15 AM


Since I was speaking of wonderfully designed boards I recently came accross 
a warpage problem on a eight layer board that caused problems.
     
I was wondering if anyone here would have any suggestions in case it comes 
up again.
     
        ----------------    Cu                  1 
        ~~~~~~~~~~~~~~~~    7628
        ~~~~~~~~~~~~~~~~    7628
        ----------------    .008 core           2/3 
        ~~~~~~~~~~~~~~~~    1080
        ~~~~~~~~~~~~~~~~    1080
        ----------------    .008 core           4/5 
        ~~~~~~~~~~~~~~~~    1080
        ~~~~~~~~~~~~~~~~    1080
        ----------------    .008 core           6/7 
        ~~~~~~~~~~~~~~~~    1080
        ~~~~~~~~~~~~~~~~    1080
        ----------------    Cu                  8
     
with the 7628 layer being required for controlled impedence work.
     
This ties into my previous post about designers having open minds.