The levels were not set arbitrarily. They were set on basis of ionic residues causing vesiccation & subsequent failure of military assemblies in high humidity environments (Vietnam). Specifically, ionic residues from RMA fluxes on conformally coated assemblies- most often radios. (See Navy report MRR-3-72). Mechanization of the original manual ionic testing method led to the different nbrs used for the various automated test instruments, as published in Navy report MRR-3-78. I wrote a column for SMT magazine on this issue; if you'd like a copy of the column, email me separately at [log in to unmask] (mailto:[log in to unmask]) as it would be stripped off if I tried to email it to TechNet as an attachment. Bill Kenyon Global Centre Consulting 3336 Birmingham Drive Fort Collins, CO 80526 Tel: 970.207.9586 Cell: 970.980.6373 **************It's Tax Time! Get tips, forms and advice on AOL Money & Finance. (http://money.aol.com/tax?NCID=aolcmp00300000002850) --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------