Jack, As others have indicated, most good FR4s will handle going down there just fine. In a prior life back in Minneapolis, we took product down to -65°C to stress test it and the board was never the problem (parts on the other hand.....). If you going for a wide range say -40°C to +80°C on a routine basis, spec a better FR4 material. One other thing you have to watch out for is that clock rates/edge-rates/timing can get a little faster when one goes colder and slower when you get hotter. So something that works at 0°C or even -20°C may not handle -40°C. Components can also not handle those temps, so a good review needs to be done. Best, -Jeffrey Jeffrey A. Jenkins Sr. PCB Staff Designer, CID+/CIT L-3 Communications, Linkabit Division Work: 858-552-9832 Email: [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson Sent: Wednesday, June 01, 2016 10:36 AM To: [log in to unmask] Subject: [TN] FR4 in COLD environments Has anyone ever heard anything about the reliability of circuit boards in cold environments? (continuous -40C) I couldn't find anything on TechNet or in the Printed Circuits Handbook... thanks, Jack ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________