This isn't a very useful response, perhaps, but the question is an interesting one. I offer some additional considerations/mind benders when contemplating the answer to this: 1) Moisture absorbtion depends on the material(s) the board is made from, and the overall amount of moisture absorbed will be related to the volume of the materials used. 2) The material volume depends on the board design and is therefore a bit variable. 3) Opportunity to absorb moisture depends on humidity, temperature and time. 4) Tracking moisture exposure depends on having an army of arithmeticians or alternatively a tracking system such as our friend Francois Monette has to offer. What we need here is some way of determining a Moisture Sensitivity Category for the various materials and their combinations, as used by component manufacturers and a means of determining the rate of moisture take-up for any given design - quite a career for somebody. On the other hand, you can simply pursuade your fab house to pack your nice, new, dry boards in individual sealed bags with some desiccant that you don't open until the moment you need them (or reseal properly after in-coming inspection) on the line. If the boards have been lying around for a year or so (in their sealed bags), and/or you're in any doubt about how dry the boards are, you can then bake them out for about 2 hours at 90 deg C just prior to use. This last has been common practice for many years, although I object on principle to having to do this - one more thermal excursion too many for the board. Call me old-fashioned, but why look for ways to make life so complicated, when a little management and control can save a lot of unnecessary effort and cost? (Sorry, Francois!). Peter Duncan MAURY HARRIS <MAURY_HARRIS To: [log in to unmask] @EFTC.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Sent by: Aero/ST Group) TechNet Subject: [TN] PWB Moisture <[log in to unmask] ORG> 01/16/02 04:05 AM Please respond to "TechNet E-Mail Forum."; Please respond to MAURY HARRIS Anyone, What is the max absorbed moisture a PWB may have prior to reflow soldering? Also, what IPC or Mil-Spec addresses PWB moisture? Thank you, Maury Harris EFTC-SCO Engineering 602 282-5179 [log in to unmask] --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 --------------------------------------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. Thank you.] --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------