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Nominal With Uneven Tolerances

Printed From: PCB Libraries Forum
Category: PCB Footprint Expert
Forum Name: Questions & Answers
Forum Description: issues and technical support
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=2074
Printed Date: 19 Nov 2024 at 12:36am


Topic: Nominal With Uneven Tolerances
Posted By: ransonjd
Subject: Nominal With Uneven Tolerances
Date 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  http://www.diodes.com/_files/packages/5676605.gif" rel="nofollow - 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


Replies:
Posted By: Tom H
Date 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.



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