Bob, My direction and findings in DS are in complete agreement with what you've said. I've established a fairly sizable extensive empirical database that I used to establish scale factors for front end plotting. Just to add more twist, vendor A vs. vendor B adds further variation within the stack. I believe this to be related to resin source (?). [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: dimensional stability Author: [log in to unmask] at SMTPLINK-HADCO Date: 12/13/95 12:15 PM To: [log in to unmask] In-Reply-To: your message of Tue Dec 05 08:32:58 EST 95 Content-Type: Text I definitely agree that the current IPC test has no correlation with re-lamination results. In my opinion there are two issues: amount of shrinkage and consistency of shrinkage. Many factors effect both: lamination pressure, thermal expansion (TCE) mismatches, residual strain, Cu pattern effects, etc. Consequently there is no simple test that predicts shrinkage! I gave 2 papers (published in the proceedings) at the last IPC meeting on the effect of C-stage parameters on re-lamination shrinkage. In our experiments we looked at total shrinkage and shrinkage variation in actual MLB boards. Independent variables included C-stage resin content, C-stage lamination conditions, C-stage stress relaxation, glass style, and B-stage cure level. The bottom line is that resin content is the major factor. I believe this is because resin content has a first order effect on TCE, and lamination shrinkage is mostly driven by the TCE mis-match between the innerlayer and the finished board. This means that looking at the C-stage properties is only half the story. We also have to look at the B-stage, the pattern, and the other C-stage layers used in the MLB. In other words, there is no single measurement that can be made on a laminate to predict re-lamination shrinkage. The only possibilities for predicting re-lamination behavior is to have a physical model that includes all important parameters in the MLB or to use empirical results based on actual measurements on similar designs. We are now using the latter approach, but hope to move to the former as our understanding improves. I plan to give a paper at the Spring IPC meeting on this topic. Bob Holmes AT&T Bell Labs [log in to unmask] ------------- Begin Original Message ------------- Subject: Re: LAMINATE DIMENSIONAL TESTING Resent-Date: Tue, 05 Dec 95 08:32:58 EST In my experience the current IPC test used by laminators to check dimensional stability has no correlation to dimensional stability results after multilayer lamination at a PCB shop. Is IPC investigating a different test method or