Wow Jan, You have: "PCBs approx 450mm long, 50mm wide, 1.7mm thick, 12 layers, 17u copper inner layers, Isola IS420 material, boards are produced with longest dimension in warp direction in PCB production panel" —and you expect a 75um tolerance after subjecting the PCB to board drying and leadfree reflow. Just consider that in PCBs you are marrying 4 different materials [laminate, prepreg, woven glass-fiber reinforcement, copper] together all of whom have significantly different physical properties, particularly at different T's and in different directions. The laminate (which is fully cured) and the prepreg (not fully cured) have different resin contents, go through glass transition (which changes molecular structure and is not fully reversible, only nearly so), start to decompose at SAC solder T's (actual weight loss, which is irreversible). The glass-cloths is in your PCBs laid up with the warp direction in the longest dimension in the PCB production panel making your PCBs quite non-uniform in the x and y directions [the normal practice is to alternate warp and fill directions on alternate layers to equalize the different properties in the warp and fill directions—even with that, it is not uncommon to measure CTE-values different in x and y by as much as 2 ppm/C]. The copper layers are mostly etched away in irregular [in the sense of physical behavior] patterns. —and you expect a 75um tolerance after subjecting the PCB to board drying and leadfree reflow?! Werner Future workshops: Pb-Free Soldering Processes—Survival, Quality, Reliability, July 17/18, Thal, Switzerland Pb-Free Soldering Processes—Survival, Quality, Reliability, July 21/22, Bad Segeberg, Germany Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18, O rlando Reliability Issues with Lead-Free Soldering Processes, September 22, Schaumburg Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture, ENIG), September 22, Schaumburg Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia Solder Joint Reliability: Parts 1 & 4, Oct. 17, Timisoara, Rumania Solder Joint Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia ************** Gas prices getting you down? Search AOL Autos for fuel-efficient used cars. (http://autos.aol.com/used?ncid=aolaut00050000000007) --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------