Hi Chris
There are two main components of Instability. The laminate layer can shrink 
when it first sees a temperature above Tg after removal of copper. The 
second factor is the bonding process and involves both the materials and the 
process. Check this out by including an unetched but bake stabilised inner 
layer and see how much it shifts. You may also get some clues from measuring 
the size of aluminium interleavers before and after pressing.
If you are interested in a more in depth discussion I am on 
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From: [log in to unmask]
To: [log in to unmask]; Dave Heywood
Cc: [log in to unmask]
Subject: Dimensional Stability
Date: 26 May 1997 10:48

<<File Attachment: ENVELOPE.TXT>>

We are planning to do a study on dimensional stability of pwbs. Right now
our focus is on the laminate material and cores. We are seeing different
amounts of shrinkage depending on design complexity, cloth type, copper
etc...In addition this shrinkage appears to be inconsistent from lot to lot..

We understand that resin content of prepreg is a factor.
In reference to Printed Circuts Handbook by Coombs (sec. 23.2.3) 40-60 %
resin content by weight is desirable. What happens to dimensional
stability if we go outside that range? What kind of SPC are you doing to
control resin content?

We would also like to know what the main variables in prepreg
fabrication (relative to dimensional stability) are, and how the rest of
the industry is controlling these variables.

All input is highly appreciated.

Chris Davison

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