Chet,
        You're not going to believe this but I've seen as much as 50%
     difference. Same job, same artwork, same lay-up...etc, only different
     vendors. Another variable (as you mentioned) that I watch closely is
     variation within the lot. This is another issue that can be seen from
     vendor A vs vendor B. 
        Gang...keep in mind that most of the time, this stuff doesn't 
     greatly impact low layer count simple MLB PCBs. It's the "cutting 
     edge" stuff that these subtle (but cumulative) changes can greatly
     impact.
     
     Dhoover


______________________________ Reply Separator _________________________________
Subject: Re: dimensional stability
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    12/14/95 12:43 AM


I noted Dave Hoover's response to the question about d.s. and he suggests 
resin souyrce as the reason for variability between vendor "A" and "B".  I 
would suggest other possibilities such as treating tension, fabric tension 
control at the weaver (also lot to lot!), etc.  Unfortunately there are 
probably also phantom variables.
     
Dave, a question.  What is the magnitude of the "A" vs "B" vendor difference 
in d.s. with for example FR-4?  Anybody else have any data (or gut feel) 
regarding the between-vendor variability for the "same" resin system?
     
Chet Guiles
Arlon