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Stencil Window Pane Design Example for QFN

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=2481
Printed Date: 22 Nov 2024 at 6:40pm


Topic: Stencil Window Pane Design Example for QFN
Posted By: jdda167
Subject: Stencil Window Pane Design Example for QFN
Date Posted: 09 May 2019 at 9:24am
Hi, 

I'm trying to figure out how library expert software calculates the stencil squares for exposed/thermal pads of QFN and QFP packages I know it is recommended to make a reduction of 40 or 50% of the area, but I would like to know how many squares are in total for a window pane design and how I can calculate the pitch between those squares? 

I saw some information from IPC-7525 but i really don't understand those formulas. 

It would be possible to give me a simple example for a 3 x 3 cm square thermal pad? 

I’d really appreciate your help.

Thanks for your time
David D.


Replies:
Posted By: Tom H
Date Posted: 09 May 2019 at 9:46am
All Thermal Pad calculation settings are in "Preferences > Rules". 
  1. Thermal Tab Solder Mask (default is 0.00)
  2. Thermal Tab Pattern Defined Solder Mask (default is unchecked)
  3. Thermal Tab Paste Mask Reduction (default is 50%)
  4. Thermal Tab Minimum Pattern Space (default is 0.20 mm)
The Library Expert Enterprise user can change any of these values. 

If you are using the Library Expert Pro, all these settings are in the "Rules" tab. 

If you want to fully control the Paste Mask Aperture opening, the Aperture Gap and the number of Apertures, then move the part to FP Designer and edit the Pad Stack > Paste Mask in the Pad Stack Manager. 



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