Joe I assume the board finish is HASL. I saw this phenomena many years ago immediately after installing one of the first HASL systems. It was determined that the impurities came from flux entrapped in the soldermask during HASL. A very aggressive cleaning process was installed immediately after HASL which resolved the issue. Best regards Lee J. L. Parker Ph. D. JLP Consultants LLC 804 779 3389 ----- Original Message ----- From: Kane, Joseph E (US SSA)<mailto:[log in to unmask]> To: [log in to unmask]<mailto:[log in to unmask]> Sent: Thursday, May 07, 2009 9:12 AM Subject: [TN] PB Surface Contamination A cleaned bare PB is exposed to bake or reflow, and comes out with measurable ionic contamination. The board is dirtier at the surface after a heat excursion. The contamination isn't coming from the oven, handling, or anything external. Heat causes something to move from the inside of the board to the outside. We haven't done any ion chromatography or other testing yet to run this down, but has anyone heard of or experienced anything similar? In our normal process, we clean everything multiple times, but if the contaminant builds up under solder mask, or in other areas that are difficult to clean, we could have SIR or corrosion problems around fine surface features or in high voltage areas. And if this ionic contamination doesn't just move up to the surface, but is somehow moving around inside the board, could it collect in some places and lead to CAF or other problems? Joe Kane BAE Systems Johnson City, NY --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask]<mailto:[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]<mailto:[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]<mailto:[log in to unmask]>: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives<http://listserv.ipc.org/archives> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16<http://www.ipc.org/contentpage.asp?Pageid=4.3.16> for additional information, or contact Keach Sasamori at [log in to unmask]<mailto:[log in to unmask]> or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------