NICK-The aspect ratio that is being discussed is for the plating of said holes, therefore, your vendor should be talking about an aspect ratio of drilled hole to board thickness over base laminate, not the nominal finished plated hole. But, my vendors are taking this aspect ratio from the nominal finished plated hole (which does help us designers). We don't really have a issue with this, being that a 6:1 aspect ratio on a .062" board would allow a .010" finished hole (my smallest hole is a .012 via). You had also stated that "the drilled hole size is up to the fabricator", this is not completely true, your internal pad stacks are to be figured, for your annular ring, to the drilled hole not to the plated hole. So you, or your librarian should know what tool your fabricator is using to achieve not only the required finished hole but equally important, your required annular ring. This may be bad news if you are now figuring your internal annular ring to the finished hole! Remember that the external annular ring is only figured from the plated hole. Question... My fabrication drawings state: "FABRICATE AND TEST PER IPC-RB-276 AND..." this spec is obsolete and replaced by IPC-6011 and IPC-6012 AS OF 7/96. Has anyone switched over? Dan Lorinser BFGoodrich Aerospace Burnsville, MN. [log in to unmask] >>> Wander, Nicholas G RV <[log in to unmask]> Jan 2, 1997 4:49 pm >>> This may sound like splitting hairs, but I think there is some confusion (maybe only on my part) about whether the finished or the drilled hole size should be used. In the example below, if the .020 diameter is the nominal finished hole size and the hole is drilled .025 diameter, the aspect ratio based on the drilled hole would be 2.4 to 1. IPC-T-50E defines aspect ratio as "The ratio of the length or depth of a hole to its preplated diameter". I assume this means that the drilled hole size, not the finished hole size, should be used. >From the designers' viewpoint, using the finished hole size would be more convenient, since this is what is usually specified. The drilled hole size is up to the fabricator. Nick Wander Printed Circuit Engineering Unisys Corporation Roseville, MN [log in to unmask] ---------- From: David Bergman[SMTP:[log in to unmask]] Sent: Tuesday, December 31, 1996 10:05 PM To: Isaac Stringer Cc: [log in to unmask] Subject: Re: Aspect Ratios Sure, Aspect ratio is the thickness dimension of the PWB divided by the diameter dimension of the plated thru hole. So an 0.060 inch thick pwb with a 0.020 inch diameter pth would have an hole aspect ratio of 3 to 1. Regards __________________________________________________ David W. Bergman, V.P. of Technical Programs IPC 2215 Sanders Road Northbrook, IL 60062-6135 847-509-9700 x340 Phone 847-509-9798 Fax email [log in to unmask] www http://www.ipc.org faxback support 800-646-0089 --------------------------------------------------- On Tue, 31 Dec 1996, Isaac Stringer wrote: > Greetings: > > Would someone be so kind as to explain 'aspect ratios' in a way > that will make sense to someone who understands hole sizes and > trace width/space? > > Thank you! > > Isaac Stringer > KML Engineering Corp. > [log in to unmask] > > > > ************************************************************************** * > * TechNet mail list is provided as a service by IPC using SmartList v3.05 * > ************************************************************************** * > * To unsubscribe from this list at any time, send a message to: * > * [log in to unmask] with <subject: unsubscribe> and no text. * > ************************************************************************** * > * If you are having a problem with the IPC TechNet forum please contact * > * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * > ************************************************************************** * > > ************************************************************************** * * TechNet mail list is provided as a service by IPC using SmartList v3.05 * ************************************************************************** * * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ************************************************************************** * * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ************************************************************************** * *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************