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Dual Flat No-Lead (DFN) -- Rounded Rectangle

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=1447
Printed Date: 18 Nov 2024 at 8:16pm


Topic: Dual Flat No-Lead (DFN) -- Rounded Rectangle
Posted By: mike_aes
Subject: Dual Flat No-Lead (DFN) -- Rounded Rectangle
Date Posted: 17 Oct 2014 at 8:30am

Not sure if this is really a bug or not. 

In User Setup Preferences under "Dual Flat No-Lead (DFN)" for the "Default Pad Shape" only Rectangle is available. 

There is no Rounded Rectangle option. 

Not sure if this is due to IPC specs or if this is a slight bug?

Thanks, Mike


Replies:
Posted By: Tom H
Date Posted: 17 Oct 2014 at 10:26am

The DFN and LGA are "Bottom Only" terminals.

The solder joint goal for DFN's is 0 (zero) and the only pad periphery is the lead and manufacturing tolerances. It's a very small periphery (annular) solder joint and rounded corners do not work well.

The solder joint goal for micro-miniature DFN pad size is equal to the lead size and subtracts -0.04 mm to compensate for the lead and manufacturing tolerances. We can't have exposed component leads without a pad under them.

However, the QFN (where the lead goes all the way to the component body edge and up the side 0.20 mm) should have a Rounded Rectangle pad shape. So we're adding that option in V2015.01 as a new feature.




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