At 02:19 PM 9/1/2001 -0700, Abdulrahman Lomax wrote:
By the way, I'd really like to know more about the warping allegedly 
produced by asymmetry. Has anyone actually seen this and verified that the 
asymmetry was the problem? I have a little trouble imagining a few mils of 
very ductile copper having enough strength to move the fiberglass around.

As for asymmetrical layering, I have often wanted to make an odd-layered 
board.  I would well imagine that one could make an odd layered board with 
a say, a center single-sided core of .010 in with prepreg gluing it to two 
other double sided cores of say .020. for an overall thickness of .062 in. 
with 5 layers.  I don't think this would warp significantly, but I have 
never tried it.  Constructing such a board would be mostly of novelty and 
academic value, since he economical value of such a stackup comes into 
question when you consider than it costs hardly any more to make that 
center core double-sided.  I suppose this is why I have never used company 
money to create such a board, but always wanted to hear from someone who 
tried it.
I can sure tell you that even if you use a symmetrical stackup, you can get 
some nice 75+ mil warping on a 4" X 5" board using such supposedly 
compatible laminates as Rogers 4003 and FR4 on either side of a 4 layer 
board.  Luckily in our application, minor warping usually isn't a problem.

Frank

Frank Gilley
Dell-Star Technologies
(918) 838-1973 Phone
(918) 838-8814 Fax
[EMAIL PROTECTED]
http://www.dellstar.com

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