Harry,

I've seen every kind of layer stack-up imaginable.

Board warpage is mainly caused by the uneven distribution of Copper
Thickness. 

If you have one plane that is out of order and call out 70um Copper
Thickness (2OZ) your board will warp when the heat is applied either through
fabrication lamination our plugging your assembled board into a voltage
source.

The solution is "Balanced Copper Thickness" throughout your design.

Tom H 


-----Original Message-----
From: Harry Selfridge [mailto:[EMAIL PROTECTED]
Sent: Wednesday, July 21, 2004 10:28 AM
To: Protel EDA Forum
Subject: Re: [PEDA] Board warpage?

It isn't an odd number of PAIRS that causes problems - it is an odd number 
of LAYERS.  There are some advanced fab techniques that can reliably 
produce boards with odd number of planes or odd number of signal layers; 
however, there are very few fabs I would trust to do it.  You can sometimes 
get away with odd number stackups, but it will eventually bite you in the
butt.

Six layers is a common balanced stackup - provided there are an even number 
of planes, and even number of signal layers with reasonably distributed
copper.

At 01:56 AM 7/21/04, you wrote:
>SNIP
>Some say that an odd number of layer pairs can cause problems, indeed we 
>had problems with 6 layers at first, though we now use 6 layers to great 
>success.  Problems with that were caused by bad process control, not the 
>design (though the manufacturer tried to blame design at the time!!)
SNIP 






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