Kaye, the addition of material to the exterior surfaces of PCB's does little to prevent moisture absorption. If you carry out periodic weight gain measurements under RTCA DO160 humidity testing conditions (we always use category B, the 10 day test) on a resist coated PCB, you find that better coating materials reduce the absorption rate by about 20%, most by 10%, but after 4 days of humidity exposure the PCB's are just about saturated (that equates to about 0.7% for a basic FR4 and 2% plus for some aramids), irrespective of what you have on the outside. Hope this is of some help. Regards Ian Fox Goodrich Engine Controls -----Original Message----- From: Kaye Clayo [mailto:[log in to unmask]] Sent: 11 July 2003 16:38 To: [log in to unmask] Subject: [TN] Low moisture absorbing soldermask Dear Technet: I have just been asked if there is a soldermask that has a low moisture absorption property. We have a pcboard that uses Taconics TLC material, which is absorbing moisture, and the engineer would like to "encase" the board with a low moisture absorbing soldermask to solve this problem. Does anyone know of anything that will work, or another way around this problem? The engineer also asked me if anyone knew how to relate IPC-TM-650 2.6.2.1 "Water Absorption, Metal Clad Plastic Laminates" to real life. What he means is, how does this test method, which dunks a pcboard into distilled water for 24 hours, relate to 70% humidity at 23C. Thank you for your help. Kaye Clayo Sr. P. C. Board Designer Keithley Instruments, Inc. CONFIDENTIALITY NOTE: This message is intended only for the use of the individual or entity to which it is addressed and may contain information that is privileged, confidential, and exempt from disclosure under applicable law. If the reader of this notice is not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately. --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------