Thermal Pad and Paste Mask Apertures

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   If a bottom pad of a QFN for example, has multiple paste mask openings generated from PCB Libraries, do these openings need to have rounded corners, or do the fabricators handle the issue with 90 degree corners on stencil openings automatically?
I know the bottom pad itself can have rounded corners.

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pcbfreedomcad Members Profile Send Private Message Find Members Posts Add to Buddy List Active User Joined: 09 Jan 2024 Status: Offline Points: 15	Post Options Post Reply Quote pcbfreedomcad Report Post Thanks(0) Quote Reply Topic: Thermal Pad and Paste Mask Apertures Posted: 6 hours 8 minutes ago at 3:19am
	If a bottom pad of a QFN for example, has multiple paste mask openings generated from PCB Libraries, do these openings need to have rounded corners, or do the fabricators handle the issue with 90 degree corners on stencil openings automatically? I know the bottom pad itself can have rounded corners.



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 6022	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 1 hour 48 minutes ago at 7:39am
	All out Texas Instruments footprints on www.pcblibraries.com/POD that have thermal pads, have the exact checkerboard pattern dimensions and spacing as their datasheets provide. Including 0.05 mm corner radius. These parts include QFN, SON, QFP, SOP, PSON, PQFN, DPAK with thermal pads. There are approximately 40,000 TI footprints with thermal pads on the Parts on Demand cloud database. The only way to accomplish this is to build the footprint using the calculator and setup all the TI package and footprint dimensions and save to FPX for the 3D STEP model. Then move the footprint to FP Designer for customizing the paste mask apertures in the thermal pad stack. Then save to FPX as the real footprint. Rename the Calculator footprint and Physical Description to match the FP Designer data. Output to CAD the FP Designer footprint footprint first. Then open the Calculator footprint and create the 3D STEP only and overwrite the FP Designer 3D STEP model. Then import into your CAD tool and you'll get the perfect mfr. recommended pattern with a high-quality 3D STEP model.
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