Hi Werner: I was referring to THT holes not SMT holes. This is what some PCB vendors go by to get the final hole size with tolerances after plating it. Their first choice would be to add 6 mils and the last choice would be to add 5 mils to the nominal hole size to find a standard drill # to perforate the board. Best Regards, Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier Sent: Friday, April 27, 2007 2:50 PM To: [log in to unmask] Subject: Re: [TN] "plated shut vias" Ramon, What you suggest, "we added...6, 7, 8 or 5 mils...[to the] specified...final hole size...to find the drill size", is very bad practice. How do you know how much inner land ring width is left or whether you have break-out? It is the drilled hole diameter that needs to be used to determine via reliability [just look at all the data and documents, like IPC-TR-578, IPC-TR-579, IPC-TR-486, IPC-D-279, they are all in drilled diameters]; it is the drilled hole diameter that determines the aspect ratio, it is the drilled hole diameter that gives you an idea as to how difficult it is to plate good copper into the hole. Going with the finished hole diameter was necessary when we used through-hole technology, but it is totally outmoded nowadays. Werner ************************************** See what's free at http://www.aol.com. --------------------------------------------------- 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 -----------------------------------------------------