Tom: Are these boards gold plated? If so, I would guess the color change was caused by cobalt. Some gold plating baths have cobalt as a component of their chemical makeup. If the silk screen ink is porous or not fully cured/polymerized the cobalt can be absorbed into the surface of the ink during plating. When heated (reflowed) it turns purple. Old-timers in the bare board business will remember this same effect "Purple Plague" causing the laminate to turn purple usually after fusing. We could make it go away by oxidizing it using a strong UV (200 watt/inch)light source. Regards Mike Barmuta Staff Engineer Fluke Corp. Everett WA 425-446-6076 -----Original Message----- From: Tom Parkinson - Quality System Manager - WinTronics, Inc. [mailto:[log in to unmask]] Sent: Wednesday, January 29, 2003 12:29 PM To: [log in to unmask] Subject: [TN] Silk Screen Goes Purple Purple?! We just finished running a batch of 15 PCBs through reflow and noticed on 2 of them, the silk screen changed from white to a very even shade of semi-dark purple. The change was uniform across the entire board. The boards were not the first or last ones through the reflow, no changes were made to the profile. Contacted the PCB house and they said they have never seen anything like it. Any ideas?? --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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/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 1.8e 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------