Author Topic: Why and when use round edges in SMD pads?  (Read 368 times)

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Offline bittumblerTopic starter

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Why and when use round edges in SMD pads?
« on: January 20, 2025, 10:07:28 am »
In the Kicad footprint libraries, a lot of SMD pads have round edges. But some of them have rectangular pads with "pointy" edges.
Also many vendor data sheets show rectangular pads, without round edges.

What are the advantages/disadvantages of round edges?
When to use round, when to use pointy edges?

TiA
« Last Edit: January 20, 2025, 10:12:53 am by bittumbler »
 

Offline eleguy

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Re: Why and when use round edges in SMD pads?
« Reply #1 on: January 20, 2025, 10:52:04 am »
In lower frequencies, if not considering the heat dissipation, the shape - instead it looks visually different - does not matter too much. But when working in higher frequencies the shape, size and transition from a trace to the pad do affect the impedance and has to be therefore treated more carefully.

Here is some discussion about it

 
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Offline PGPG

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Re: Why and when use round edges in SMD pads?
« Reply #2 on: January 20, 2025, 11:45:58 am »
The paste comes off more easily from rounded corners.
 
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Offline DutchGert

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Re: Why and when use round edges in SMD pads?
« Reply #3 on: January 21, 2025, 06:45:59 pm »
Rounded edges should be the standard imo. Main reason being that this results in a rounded stencil opening that is much more reliable in terms of solder paste application.

In my prev. company (automotive) rounded corners where mandatory

In high speed designs you can add arcs to more gradually go from a thin trace to a thick pad and more gradually adjust the impedance that way.

But 95% of the cases its just for DFM purposes.   
 


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