Gregg, We have seen PbC too and found it harmless. People's reaction was understood because it can look hairy in high mag, and even more disturbing when you have MIL or SPACE people hanging around. A cotton tip dipped in a weak acidous solution removed it in seconds I remember. Ingemar -----Original Message----- From: Gregg Klawson [mailto:[log in to unmask]] Sent: den 31 januari 2001 15:33 To: [log in to unmask] Subject: [TN] Lead carbonate growth during humdity testing We have just completed a 10-day cycled system-level humidity test of several board assemblies. The boards are mixed TH/SM predominately SM, ENIG finished. Bias was applied for about 45 minutes once every two days during the test. At the conclusion of the test microscopic examination (7x-40x-200x) of all the assemblies revealed shiny metallic appearing flakes around the surface mount pads, especially around and between the leads on some PQFP devices. One board had a significant amount of this flake-like material piled up between some of the PQFP pads/solder joints. SEM-EDS analysis of the flakes showed strong Pb, C and O - lead carbonate. The analyst stated that this looks like lead carbonate crystal growth. The flakes readily dissolve in acetic acid. I have trouble believing that this crystalline lead carbonate growth over ten days is "typical" (carbonate formation from atmospheric CO2), we have not seen type of corrosion before. We had a cleaning issue with these boards, so many of them had to be run through our in-line cleaner up to 10 times. Armakleen 2000 (carbonate based) is used in our in-line cleaner. We checked the cleaned boards using an Ohmegameter for any evidence of cleaner residues and found none. So I'm at a loss to explain why we had some growth on all boards and significant growth on one board. One engineer suggested we "over cleaned" the boards and we laughed at the time but now I'm not so sure. The other concern is whether lead carbonate formation over time will cause a reliability problem. I've been told of failures due to this under extreme environments. It appears that the carbonate itself is not conductive and will not cause an electrical short but I'm guessing some of the reaction products with moisture may produce some conductivity. Thanks again for your comments. Best regards, Gregg Klawson General Dynamics Communication Systems Taunton, Massachusetts, USA mailto:[log in to unmask] The views expressed are the author's and do not necessarily reflect the official position of General Dynamics or any of its subsidiaries. --------------------------------------------------------------------------------- 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 --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------