Terry- much of what you say is correct. But we have to look at some of the details. 1. The ionic cleanliness test was originally developed to determine if conformally coated military equipment would survive the harsh temp/humidity conditions of S.E. Asia. In the words of the day, is the floor clean enough so we can put down the wall-to-wall carpet? 2. While most of the PWAs were assembled with RMA moderate to high solids rosin fluxes, many of the electronics makers wanted to use stronger fluxes to cope with the marginal component solderability of the era. Thus we soon had the RA-Mil activity level fluxes to help with that issue. 3. The designs were generally through-hole, surface mount wasn't in common use until much later, esp. for mil use. Thus flux residue entrapment wasn't the issue then that it became after the adoption of low clearance restricted cleaning agent flow SMT parts. 4. The Task Group work you have cited pointed out other concerns that weren't big issues with PTH/high solids fluxing agent designs; such as the 'dead band' in cleaning instrumentation response. 5. All in all, these deeper investigations helped us all to understand some of the nuances of ionic cleanliness testing, which had taken on a standing that was interpreted as an absolute guarantee of reliability, when it was really developed as a process monitoring tool. Now in the test's favor, the level was set to reflect ionic contamination levels based on clean and failed PWAs from the field (U.S.Navy MRR-3-72), and confirmed by the lab work of W. B. Wargotz at Bell Labs (see my previously offered SMT column for the reference) so the pass/fail was not arbitrarily chosen. 6. To address your point about spot or localized high levels on ionics, Wargotz has published on his work of making mini-cells on the PWA surface by gluing a piece of Pyrex tubing to the surface using RTV, then putting in a controlled volume of test solution, a micro conductivity or resistivity cell to obtain spot readings in known entrapment areas. Hopefully, such work would result in design changes so the overall average ionic contamination level would be indicative of good field performance. (This paper may have given at one of the IPC World Conferences, I'll have to check my files to see if I still have a copy). 7. Terry- thanks for bringing your points up, so they can be discussed in a way that helps members of the TN community better understand ionics and testing. Bill Kenyon Global Centre Consulting 3336 Birmingham Drive Fort Collins, CO 80526 Tel: 970.207.9586 Cell: 970.980.6373 **************Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp00300000002851) --------------------------------------------------- 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 -----------------------------------------------------