Bill, Your reported difficulties imply that you may have some ionic residues on the assembly surface and because a conformal coating breathes, water vapour can pass through and create osmosis. Osmotic pressure up to 800 bar (zinc salt) can be evidenced. Result - blisters and circuit failure as the solubalising residue bridges conductors or component legs. I assume the coating has been fully polymerised before these tests? That the coating has been applied to the correct thickness? That you have attained a suitable cleanliness level??? Ah! Cleanliness --- Please refer to my previous offerings on the subject of SIR testing or Circuit Reliability Testing. If would like a further copy let me know and I will send it offline - too many TechNetters have already received multiple copies. Graham Naisbitt Concoat Ltd Email: [log in to unmask] Alasan House, Albany Park Tel: +44 (0)1276 691100 Camberley, Surrey GU15 2PL UK Fax: +44 (0)1276 691227 -----Original Message----- From: TechNet On Behalf Of BROMLEY, Bill Sent: Friday, October 17, 1997 4:20 PM To: [log in to unmask] Subject: [TECHNET] ASSY: Temperature Cycling Test Failures This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. ------ =_NextPart_000_01BCDAEE.8E901490 Content-Type: text/plain We are experiencing temperature cycle (-37C to 55C) test failures on mixed technology (thru-hole one side, SMT other side) PWB assemblies coated with Polyurethane per Mil-I-46058. The same assemblies pass static temperature testing at the low, ambient and high points of the temperature range. Uncoated assemblies will pass the temperature cycle test. It is suspected that small bubbles in the conformal coating (within allowable size per specification criteria) are accumulating condensation during temperature transitions, causing bridging between conductive surfaces on the SMT components. Has anyone experienced similar problems? Bill Bill Bromley Lead Designer Lucas Aerospace PSA MailStop D960 777 Lena Dr. Aurora OH 44202-8025 USA voice: 330-995-1000 ex 3092 email: [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. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ############################################################## ############################################################## 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. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################