The difference in pressure between high and low vacuum is very small. The difference in high vacuum and ultrahigh vacuum is only a few molecules that are attached to the walls of the chamber or trapped in between spaces creating virtual leaks. Removing one atmosphere of pressure or about 32 inches of mercury at sea level is all that can be attained. My understanding of the vacuum in the drying process is that it is used to move any moisture out of the chamber, followed by refilling it with dry air, thus creating an imbalance of moisture and pressure between the chamber and the inside of the parts, which will leak out the moisture inside of them through their porous bodies. When this cycle is repeated over and over, it speeds the drying of the components. The temperature keeps the water molecules volatile and the vacuum dries the chamber. It makes a lot of sense. Even if the chamber has absence of gas pressure it will take some time for the inside of the parts to reach the same low pressure. Regards, Ramon > My understanding of the low temp moisture extraction process is that it's > carried out under partial vacuum, not high vacuum, so that the moisture > neither boils off rapidly, nor freezes - either of which would cause > delamination if it were allowed to happen. My initial skepticism about the > process was relieved after I spoke to Altos Engineering further about it, > although I would want to see the process obtain industry approval or > conduct my own tests with it before I considered adopting it as a process > here. > --------------------------------------------------- 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 -----------------------------------------------------