When I was working in a FMEA lab I did see the failure mode your fabricator describes. Do you need the via on the bottom for test? If not mask the via. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dharma Kemp-Bresett Sent: Tuesday, May 06, 2008 1:51 PM To: [log in to unmask] Subject: [TN] single sided via tenting and immersion finishes... need both fab and assy input Hello everyone, I am usually hanging on the outskirts soaking up as much info as possible from all the knowledgeable individuals on TechNet. It is always enlightening and quite often amusing so thank you all beforehand for the wonderfully entertaining education I am receiving. :-) I am looking for info from both the fabrication and assembly side for this one as apparently there are varied opinions on the subject. If you can point me to specific documentation that I can show to my customers that would be even better! A couple of years ago a fabricator/assembler recommended to us that we should tent vias (component side only) on all dogbones for fine pitch bgas as there was a chance of shorting to adjacent pads. We incorporated this into our footprints going forward as standard practice and have had no problems that I am aware of. However we recently received a suggestion from one of our fabricators that we should discontinue this practice on immersion finish boards as over the last year or so it had been observed ( throughout the industry) that this caused via barrel degradation (due to trapped solution) that in most cases was not caught till the assembly had been in the field cycling for a period of time. The recommendation given was to now encroach rather than tent these fine pitch fanouts. The specific recommendation given was 2.5-3 mil encroachment on most vias with 2mil encroachment on 8 mil vias ( the smallest we have used with this particular customer) with the understanding that the problem gets worse the smaller the via due to capillary action. The other option was plugging but that could be cost prohibative so i would like to stay away from that option if at all possible. What are your opinions on this subject and is there any specific documentation i can point my customers to that might help us determine the best course of action? Thanksin advance, Dharma --------------------------------------------------- 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 -----------------------------------------------------