Thanks All, I appreciate the insight and the humor. Regards, Martin -----Original Message----- From: Whittaker, Dewey (AZ75) [mailto:[log in to unmask]] Sent: Wednesday, April 20, 2005 10:19 AM To: [log in to unmask] Subject: Re: [TN] PCB Silkscreen Discoloration I've known a few half-baked legends in my time, who faded away due to the blend of alcohol. Dewey -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Valerie St.Cyr Sent: Wednesday, April 20, 2005 9:07 AM To: [log in to unmask] Subject: Re: [TN] PCB Silkscreen Discoloration I agree with all of what Jeff wrote; plus, in addition to the reflow temperature (which does not need to be very hot) even a prebake can discolor legend ink. Do you know if these boards were pre-baked? Many times I have found that organics circulating in the air in an oven can deposit on the ink and cause it to darken .... if not that, then it is probably the blend of ink. Valerie Jeffrey Bush <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 04/20/2005 09:51 AM Please respond to TechNet E-Mail Forum; Please respond to Jeffrey Bush To: [log in to unmask] cc: Subject: Re: [TN] PCB Silkscreen Discoloration Epoxy inks tend to be more resistant to discoloration than the acrylics that are used more widely now. 2-part epoxy inks are governed by CID-A-A-56032 and while the specific requirement for thermal resistance is not part of this standard, inks tested to this standard have good resistance to heat cycles to 288C for short durations and 150 C for as long as 75 minutes without discoloration. The acrylated inks vary in their ability to maintain color after heat cycles. Part of our qualification of new inks includes color changes and not all inks are able to remain white after even brief excursions to fairly low temperatures. The technical data sheets from the ink supplier should indicate what testing has been done and also what are the limits of exposure to thermal, chemical and mechanical conditions. Jeffrey Bush Director, Quality Assurance and Technical Support VERMONT CIRCUITS INCORPORATED 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302 Voice: 802.257.4571.21 Fax: 802.257.0011 http://www.vtcircuits.com -----Original Message----- From: Martin Butcher [mailto:[log in to unmask]] Sent: Tuesday, April 19, 2005 6:29 PM To: [log in to unmask] Subject: [TN] PCB Silkscreen Discoloration Hi All, I have a question regarding the discoloration of the silk screen ink after reflow. What can cause it other than overheating during reflow? Here is some background to this question. We received a consigned kit, processed it and shipped it about three months ago. Our profile data shows that the PCB did not reach peak temperatures above 216 deg C. We have run this product once prior with a peak temperature of 212 deg C and with no reports of discoloration. Our client has contacted their board shop concerning this and were told by the board shop that the discoloration is due to overheating. Are there other variables that could account for this? Regards, Martin Butcher, Process Engineer. --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------