Thank you (once again) Werner, Dave, and Vlad for educating me. Your information is invaluable. -----Original Message----- From: Igoshev, Vladimir [mailto:[log in to unmask]] Sent: Tuesday, January 29, 2008 3:46 PM To: TechNet E-Mail Forum; Stadem, Richard D. Subject: RE: [TN] Microvoids immersion silver Richard, Kirkendall effect is not specific to the noble metals and it's has nothing to do with the "Champaign" voids either :-) Here is a brief description of the effect: "The Kirkendall effect is the migration of markers that occurs when markers are placed at the interface between an alloy and a metal, and the whole is heated to a temperature where diffusion is possible; the markers will move towards the alloy region. For example, using molybdenum as a marker between copper and brass (a copper-zinc alloy), molybdenum atoms will migrate towards the brass. This is explained by assuming that the zinc diffuses more rapidly than the copper, and thus diffuses out of the alloy down its concentration gradient. Such a process is impossible if the diffusion is by direct exchange of atoms." Regards, Vladimir -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Tuesday, January 29, 2008 2:31 PM To: [log in to unmask] Subject: Re: [TN] Microvoids immersion silver Werner and Don. I was always under the impression that Kirkendahl voiding was a result of the noble metal's (in this case, silver) nucleation through the SJ. I always thought that this was a time-variable migration. I understand how all of the process variables described in Werner's response will affect or support the eventual void formation, but I would not expect Gaby to find anything in microsections taken immediately after soldering. Would it not make more sense to thermally cycle the SJs in order to facilitate the nucleation prior to microsectioning? -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /* Sent: Tuesday, January 29, 2008 12:35 PM To: [log in to unmask] Subject: Re: [TN] Microvoids immersion silver Hi Gaby, I take it what you are seeing are 'champagne voids.' Voids like these are 'encouraged by rough topography copper, excessive Ag thickness, some solder paste choices and rapid cool-down after reflow. But as Donald Cullen says in his comprehensive paper, it "requires the "Perfect Storm" of a rather contrived combination of parameters" to produce planar micro-voiding. Well Gaby, now you know it-you are "Perfect." ;-) Werner ************** Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489 --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------