Hey Jack, The problem is that it depends. There are several other (maybe fabricator specific) factors that may be well understood, but you need to de-correlate them before you could make a decision. that's why many times design activities simply "allow NFP removal". And "engineering punt" to the fabricator. A relatively simple way that some OEMs handle it is to include an empirical study during fabricator qualification. Delphi is probably the best known example. It works. Chris -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson Sent: Wednesday, August 04, 2010 10:15 AM To: [log in to unmask] Subject: Re: [TN] non-functional pad removal Well, maybe I should have known better than to try and summarize all the previous responses, both public and private. The goal I was pushing towards is related to the fact that the committee that just finished balloting on IPC-2614 (Board Fabrication Documentation) included an appendix with "sample notes". On the subject of non-functional pads, here are the three sample notes provided by IPC-2614: 1) Non-functional pads may be removed from inner layers at vendor's discretion 2)Manufacturers shall not remove non-functional pads 3)Removal of non-functional pads from internal layers is permissible Yes, those are notes. and maybe they are representative samples in someone's opinion, but in my opinion they don't provide any guidance to the reader and they gloss over what could be a significant reliability issue. It seems like there is enough technical knowledge on this forum, and enough people have already replied with interesting related points about the subject, that we could write at least one other note that might be more useful. Can't we come up with a note that fits MOST applications, and leave it to the user to modify it for his specific circumstances? onward thru the fog, Jack . On Tue, 3 Aug 2010 20:06:01 -0400, Werner Engelmaier <[log in to unmask]> wrote: > Hi Jack, >Here are my comments > > >So here is what I have been told about the subject of non-functional pads (NFPs): > >- Drill bits last longer if NFPs are removed - "YES > >- In some cases NFPs create anchor points for stress, and barrel cracks occur - "I THINK YOU MISUNDERSTOOD THIS. > >- Reliability is more relevant to hole diameters less than .020", remove NFPs from larger hole diameters - "RELIABILITY IS >OF COURSE EQUALLY RELEVANT, YOU JUST GET DIFFERENT FAILURE MODES DEPENDING ON DRILLED DIAMETERS: >BARREL CRACKING FOR SMALLER DIAMETERS, INNERLAYER SEPARATION/SHOULDER CRACKS FOR LARGER DIAMETERS. >REMOVING NFPs FROM SMALLER DIAMETER HOLES HAS LESS RELIABILITY CONSEQUENCES. > >- Yield may increase by reducing possibility of inner layer shorts by removing NFPs - "??? > >- NFPs only play a role with higher aspect ratios - "NO > >- Divide the hole length into three zones, and remove NFPs from the middle zone - "YES > >- High layer count with thin dielectric creates resin-starved pancake stack, remove some NFPs - "??? > >- Keep the stack symmetrical, if a connection is made on layer 8 of a 16 layer, leave NFP on layer 9 to balance the stress - " >A SYMMETRICAL STACK IS A GOOD IDEA TO REDUCE WARPAGE DURING SOLDERING; YOU CANNOT "BALANCE" [WHATEVER THAT MEANS] STRESSES THIS WAY > >- NFPs reduce voids in thin low-flow prepregs - "POSSIBLY > >- Don't remove NFPs from layers 1,2,3,n-2,n-1,n - "FOR LARGER DIAMETER HOLES > > >I assume that those working on high-tech high-reliability designs know what >they want to do and have customized their fabrication drawing to get what >they want. On the other hand, I'm concerned about the average designer who >wants to know best practices, but isn't sure how to form the note. > --------------------------------------------------- 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 ----------------------------------------------------- ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- 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 -----------------------------------------------------