PCB Libraries Forum : Specified vs calculated nominal sizes https://www.PCBLibraries.com/forum/ Fri, 01 May 2026 10:57:07 +0000 Mon, 13 Apr 2015 07:00:03 +0000 http://blogs.law.harvard.edu/tech/rss Web Wiz Forums 12.07 360 https://www.PCBLibraries.com/forum/RSS_post_feed.asp?TID=1649 <![CDATA[PCB Libraries Forum]]> https://www.PCBLibraries.com/forum/forum_images/PCBLForumLogo.gif https://www.PCBLibraries.com/forum/ <![CDATA[Specified vs calculated nominal sizes : The Tolerance Deviation of -0.10...]]> https://www.PCBLibraries.com/forum/specified-vs-calculated-nominal-sizes_topic1649_post6725.html#6725 Author: Tom H
Subject: 1649
Posted: 13 Apr 2015 at 7:00am

The Tolerance Deviation of -0.10 mm to +0.30 mm does not play into the mathematical model of the IPC-7351 land pattern calculation for the resulting pad size. You can enter -0.10 mm to +0.30 mm or +/- 0.20 mm and get the same results.
 
Also, it makes no difference if a component manufacturer only provides Nominal package dimensions. There still is a minimum of 0.10 mm +/- tolerance on every dimension. No manufacturer can produce component packages that are 100% perfect every time. i.e.: no one should ever put 0.00 for a tolerance.
 
We've been creating land pattern calculators since 2001 and while we really appreciate users to challenge the standard to find flaws or suggest a better solution. We know that some mfr. tolerances are uneven and you can put them in the calculator uneven, but the program will make them even.
 
Maybe this is something we need to look into for the V2016 Library Expert rewrite. The code is getting old and we need to create a brand new tool to make it look like 2016 to work with Windows 10 coming this October.
 
 
 
]]> Mon, 13 Apr 2015 07:00:03 +0000 https://www.PCBLibraries.com/forum/specified-vs-calculated-nominal-sizes_topic1649_post6725.html#6725 <![CDATA[Specified vs calculated nominal sizes : Usually lower and upper deviations...]]> https://www.PCBLibraries.com/forum/specified-vs-calculated-nominal-sizes_topic1649_post6718.html#6718 Author: JJonas
Subject: 1649
Posted: 13 Apr 2015 at 3:54am

Usually lower and upper deviations from nominal sizes are specified to be the same. However, that is not always the case. For example, nominal size can be specified to be 1.0 with lower deviation of -0.1 and upper deviation of +0.3. In this case your application recalculates nominal size to 1.1. This issue becomes relevant in case I select silkscreen outline to be drawn to nominal body size - I expect to have manufacturer specified width and length, not recalculated ones. What is also affected is 3D models.

Why have you chose to recalculate manufacturer specified nominal sizes?
]]> Mon, 13 Apr 2015 03:54:54 +0000 https://www.PCBLibraries.com/forum/specified-vs-calculated-nominal-sizes_topic1649_post6718.html#6718