Hi Phil: When I used to perform outgassing tests (per NASA SP-R-0022 or ASTM E595 at 125C at <10E-6 torr) at Ball Bro. in Boulder, CO I used a rule-of-thumb (developed by those kind folks) that for a 24 hour test the diffusion of volatile material, including water, was limited to 1/32 inch below the surface. This means that a typical organic material can be depleted of low molecular weight volatile material in a 24 hour period at 125C and 10E-6 torr if it is no more than 1/16 inch thick, assuming diffusion is from top and bottom surfaces. Ultrahigh vacuum systems can take days or weeks to reach vacuums like 10E-10 torr, depending upon size. Water is very difficult to desorb, especially as the number of atomic layers decreases (i.e., changes from physically adsorbed to chemically adsorbed). Some recent work at NASA (that I have not followed up on) seems to indicate that residual hydrogen and react with natural surface oxide to form water. Pat Hogue Materials and Processes Engineering Honeywell Satellite Systems Operation Glendale, AZ 85308 (602) 561-3748 ---------- From: Phil Hersey [SMTP:[log in to unmask]] Sent: Wednesday, March 24, 1999 9:00 AM To: [log in to unmask] Subject: [TN] How to get water out? I am chronically failing RGA (residual gas analysis) despite several hours of vacuum bake. I vaguely remember from my sputtering days that vacuum alone is not the best way to remove moisture - vacuum dep. machines use a "nitrogen trap". Does anyone know of better ways than vac. bake to remove H2O from PCB assemblies which will later be hermetically sealed and tested for RGA? Resp. Phil Hersey, Carson City Nevada USA ################################################################ 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 ################################################################ ################################################################ 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 ################################################################