Absolutely. Not to take us too far off topic but my opinion is give me information on what you want the end product to be. let me and my experts develop the plan to product that for you. With ever tighter boards these days, we need every advantage to keep yields up. We have seen a few drawings come across denoting drilled hole size, and in most the designer did not think to factor in accumulative tolerance. let me say that again, accumulative tolerance. Design 101 - For those that may not understand let me describe it this way, lets say my process is capable of maintaining a +/- 0.001" tolerance (laughing at the idea right now, but lets proceed). This does not mean that you should make your drawings with an overall tolerance of +/- 0.001". For example; you design a pretty tight 18 layer board, lines at 4/4 , 0.062 overall thickness. And you add the words "layer to layer registration shall be 0.001" or less". Beginning with layer image, on the 18 layers, I am allowed 0.001" shift, beginning with layer 1, and ending at 18, lets say they all shifted 0.0005" in the Y axis, that would be 0.0085" variance from layer 1 to 18. Would 0.0085" present a problem??? Well of course. accumulative tolerance. Lets say then you had layers at 0.001" off in one direction, and the drill off 0.001" in the opposite, would this present a problem? Well it might not be an issue internally but one you applied solder mask, and then for grins say solder mask is off 0.001" from the drill in the opposite direction as well, well if you've designed copper defined BGA's you've just put up to 2 mils of solder mask on the edge. But this is within the 0.001" (accumulative tolerance). Now here is where the heartburn gets you.there are few shops that can maintain 0.0025" tolerance let alone the 0.001", most shops will accept 0.003" tolerance (and possibly suffer high yield loss). So in closing (and because I am just tired of typing). Tell the fabricator exactly what you want, including what you can tolerate, what you cannot tolerate, be reasonable in your request, be receptive to their feedback, and if you designed it lousy, do not take offense, learn from those who are trying to make their living off your design as well. Franklin From: [log in to unmask] [mailto:[log in to unmask]] Sent: Wednesday, July 09, 2008 3:47 PM To: [log in to unmask]; [log in to unmask] Subject: Re: [TN] PCB Inner layer shifting Hi All, That is the reason vias should be specified as to drill diameter, not finished hole size. Werner ************** Get the scoop on last night's hottest shows and the live music scene in your area - Check out TourTracker.com! (http://www.tourtracker.com?NCID=aolmus00050000000112) --------------------------------------------------- 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 -----------------------------------------------------