PCB Libraries Forum : Nominal With Uneven Tolerances https://www.PCBLibraries.com/forum/ Sun, 19 Apr 2026 02:09:50 +0000 Fri, 27 Jan 2017 08:32:05 +0000 http://blogs.law.harvard.edu/tech/rss Web Wiz Forums 12.07 360 https://www.PCBLibraries.com/forum/RSS_post_feed.asp?TID=2074 <![CDATA[PCB Libraries Forum]]> https://www.PCBLibraries.com/forum/forum_images/PCBLForumLogo.gif https://www.PCBLibraries.com/forum/ <![CDATA[Nominal With Uneven Tolerances : I the IPC mathematical model,...]]> https://www.PCBLibraries.com/forum/nominal-with-uneven-tolerances_topic2074_post8525.html#8525 Author: Tom H
Subject: 2074
Posted: 27 Jan 2017 at 8:32am

I the IPC mathematical model, various minimum and maximum tolerances have no affect or impact on the resulting land pattern.

You can enter various minimum and maximum tolerances in Library Expert, but Library Expert will save the data as the nominal tolerance.

]]> Fri, 27 Jan 2017 08:32:05 +0000 https://www.PCBLibraries.com/forum/nominal-with-uneven-tolerances_topic2074_post8525.html#8525 <![CDATA[Nominal With Uneven Tolerances : I&#039;ve noted that Library Expert...]]> https://www.PCBLibraries.com/forum/nominal-with-uneven-tolerances_topic2074_post8524.html#8524 Author: ransonjd
Subject: 2074
Posted: 27 Jan 2017 at 8:00am

I've noted that Library Expert doesn't save the nominal, but calculates it as the mean of the minimum and maximum of a dimension.

I've been working with a few parts where the tolerances are uneven, and this means that the naming doesn't match the datasheet nominal. Dimensions D and E from this DFN provide a quick example.

Is using the mean value correct according to IPC, or is this a limitation of PCB libraries?

Cheers,
John
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