I like your statement "My general opinion about cleaning is that easiest way to clean something is if that "something" doesn't exist. On the printed board in this case,oxidation, contamination in the laminate, residues et cetera." We all know some type contamination will exist no matter the manufacturing or cleaning process used. How it affects a "steril" high vacuum environment is another matter. You have acceptance criteria during operation? Using Steve Z's logic, I would start with the least "porous" material possible then laminate it in a vacuum press, for dimensional, outgassing, and other purposes. The choice of ENIG seems right. Solder mask or not, if it is LPI it is epoxy approximating the laminate material and finished board so, I think, go for whatever is needed. Clean as required to meet specified requirements. Follow this with a good high vacuum "soak" simulating the operational environment. Then, go for it. MoonMan --------------------------------------------------------------------------------- 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 the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------------