Ed, We have seen minimal via holes, like less than .005 annular and not had a reliability issue. But there are many variables still missing, like what is your ambient operating condition and what will the joint temperature get to, vibration, and hole to lead ratio etc. Your biggest concern is valid with the CTE Z-axis and that the barrell of the via may be jeapordized when the delta Temperature takes place. Something you might consider is minimizing the hole to lead, which can be done without major artwork change and also ensure there are pads for plating to adhere to on the inner layers. Bottomline however, you shouldn't worry about reliability, unless you're warranting the work. If that is the case, you should have ability to make recommendations to maintain the barrel integrity, since you have little mechanical mechanism for keeping the lead / via intact during temperature cycling. My $.02 Rodney -----Original Message----- From: Ed Berti [mailto:[log in to unmask]] Sent: Wednesday, September 17, 2003 7:52 AM Subject: Reliability question I have a question concerning the reliability of a PCB that has little to no annular ring on the via holes on the external surfaces of a multilayer board: -there are about 100 such holes on the board -all components are through hole -the board is four layers, 0.062" thick -solder mask fills most of these via holes -the pad size is about 0.024", with a hole drill size of 0.020", and finished hole size of about 0.016" -the trace coming into the hole is 0.008" wide -there are a few locations where a trace enters a hole and there is no land (pad) at the junction of trace/hole, just the width of the trace -the specification is for 2 ounce copper finished amount The board house has 100% electrically tested the boards for shorts and opens and found no failures, and believes that the boards will be reliable. We have assembled, wave soldered and tested (before discovery of the problem) about 30 of the units and have found no failures related to this issue. The boards do not meet IPC-A-600 specifications. The customer designed the board and did not call out any IPC spec. My concern is the long term reliability of the trace to hole junction. It seems that I remember hearing of high density boards actually being designed without pads: the traces came directly into the hole. Has that been done successfully? Is the reliability questionable? Will successful thermal cycling of the assemblies indicate long term reliability? Any thoughts or suggestions will be appreciated. Thank you, Ed Berti --------------------------------------------------- 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 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- 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 847-509-9700 ext.5315 -----------------------------------------------------