Michael, Excellent posting. I really appreciate a reasoned approach to an engineering challenge. We did quite a bit of work for CERN (Claude-Pierre Marin) a few years back on coverfilm and adhesive based laminate. The most reliable adhesive for long term exposure to liquid helium in the ATLAS detector was phenolic-butyral. (Though it ultimately wasn't selected for other reasons.) It's stiffness and adhesion properties were very stable at all cryogenic temperatures. In a separate study for BEI we discovered that Acrylics were only useful down to about -35C. At -50C the bond strength was completely compromised. Your observations of an "aging" effect may be the result of polymer oxidation. Also, be careful to investigate the source of the opens. Is it a lack of support by the coverlay, or simply a failure of the adhesiveless laminate bond at cryogenic temperatures? Andy Magee Flex Guru - Consulting [log in to unmask] (937) 435-3629 ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################