Hi Kelly, The 10% rule should really be applied to traces under a certain size... and the +/-.001 inch tolerance should apply to larger traces that would be significantly out of tolerance if 10% was applied to them. The need to use a percentage tolerance comes from trying to use a fixed tolerance like +/-.001 on a trace that is too small like .006 in. width. The .001 change is width becomes very significant for these smaller width traces and that's why the adopted 10% tolerance came into play where .001 inches would be greater than 10%. Neither method stands alone as it can not describe accurately the tolerance scheme being employed. On the other hand, I believe, a combination of the 2 can accurately describe the end results in a way that can be measured and verified. I believe a uniform note could be created that could encompass all variable situations encountered and give good repeatable measurable results. i.e. - Note: All etched and/or plated features shall be held to within 10% of cad generated artwork originals, or +/-.001 inches which ever is the lesser variation in geometry. Does something like that come close to describing what is desired? Bill Brooks PCB Design Engineer , C.I.D., C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 ----------------------------- Greetings, An inconsistency in our fab specs regarding etching/plating tolerance finds me at a mental "cross-roads" regarding this subject. The spec for some of our designs express the tolerance in the form of "mils" -- +/-.001, while other spec express the tolerance in the form of a percentage -- +/-10%. In one sense, on a design w/ .010 nominal lines and spacing, these two specs are the same. However, on a design w/ .005/.005 or .004/.004 lines and spacing, using a tolerancing method of +/-.001 vs. 10% has drastically different results. I would like to see any feedback on the pro's and con's of each method. What method do you use and why? -- Kelly Kelly Dack PCB Dsnr IGT (International Game Technology) Reno, NV --------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------