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