Ken, 6 thermal cycles over the expected operating range should not create more defects than it identifies. If it does, you may want to review the construction of your product or review the promised temperature ranges over which it supposedly operates. I would also recommend contacting a reliability expert. Your ESS should be tailored towards the defects you are trying to screen. Is it poor solder joints? Defective components? Board defects? Why are you holding for 2 hours during thermal cycling? You should be able to answer these questions before you begin ESS. You should also perform functionality testing before and after ESS and have some sort of in-situ event detector attached during ESS to detect intermittents. If you have anymore questions, please feel free to contact me by email. Best Regards, Craig > -----Original Message----- > From: Chafin, Ken G. [mailto:[log in to unmask]] > Sent: Thursday, August 05, 1999 3:58 PM > To: [log in to unmask] > Subject: [TN] ESS Screening > > > A proposal has been made that all our recently designed surface mount > printed circuit board assemblies be subjected to the following thermal > cycling process: > > 1) Heat chamber to +71 degrees C as rapidly as chamber allows (but not to > exceed 15 degrees C per minute). > > 2) Dwell at +71 degrees C for 2 hours. > > 3) Ramp temperature down as rapidly as chamber permits to -40 degrees C (but > not to exceed 15 degrees C per minute). > > 4) Dwell at -40 degrees C for 2 hours. > > 5) Ramp temperature from -40 degrees C to +71 degrees C as rapidly as > chamber allows (but not to exceed 15 degrees C per minute). > > 6) Conduct the above +71>-40>+71 thermal cycle 6 times. > > 7) Retest PCB assemblies. > > Note: No power or signal is applied to units during thermal cycling. > > View #1: The thermal cycling described above will tend to screen out those > assemblies with defective components and/or workmanship faults--including > those involving solder connections. It will help identify likely infant > mortalities and assemblies likely to fail prematurely in field operation. > > View #2: The thermal cycling described above is likely to create more > defects than it identifies. The cost of performing this screening process > outweighs its benefits. > > > Our electronic equipment is generally designed and qualified to operate from > -40 degrees C to +70 degrees C. > > I would appreciate any references to personal experience or literature which > would help determine whether View #1 or View #2 is more credible. > > Thanks for any replies. > > ############################################################## > TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional > information. > If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or > 847-509-9700 ext.5365 > ############################################################## > > ############################################################## > TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional > information. > If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or > 847-509-9700 ext.5365 > ############################################################## > Dr. Craig Hillman CALCE Electronic Products and Systems Consortium University of Maryland College Park, MD 20742 (301)-405-5316 [log in to unmask] ############################################################## TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################