Many years ago I can recall a job where we took very thick multilayer boards (>.125) and ran them through an immersion tin process. Immediately after drying with an air hose, we placed the boards in a vacuum bake process to remove moisture from the board in a condition where oxidation could not occur. Immersion tin remains solderable for only a very short time. Immediately after that process, the boards were immersed into a product made by Alpha metals. I'm not sure of the number but, it was something like Alpha 826 flux coat. Anyway, you take the boards out of the flux coat then "bump" the excess flux out of the holes and then literally hang up and dry. The flux coat dried on the board and then was placed into plastic bags for long term storage. The big problem with using this process today is that it used rosin fluxes for flux coat and for the final soldering process. Back then were we able to use CFC's (Freon) to remove the flux residues. I'm not sure what kind of chemistry is available today with respect to flux coats. All I can say is that we were able to solder immersion tin boards quite readily by protecting the tin with a flux coat. Bill Kasprzak Moog Inc. (Sorry, no "whizzy" graphics) *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************