1. ## Dimension Thermal Relief Pad

Hi all,
I'm wrinting this post because I'm a bit confuse about dimension Thermal Relief Pad.
I saw IPC 2221 and IPC 2222. I read Thermal Relief in Conductor Planes paragraph but I didn't understand some thinks.

In the IPC thare is the calculation about total thermal width. (I think it is the total width of spokes ) but this number depends of the corrente max. And I dimension its as a tracks. What's the difference?
I need to calculate air gap between pad and plane. How can I to get it?
Thanks.
Bye

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2. ## Re: Dimension Thermal Relief Pad

Make it up....
The width of the individual spokes theoretically should equal the required trace length to carry the current divided by the number of spokes...
There is no air gap, only on the outer layers, just leave a spacing that is sensible (usually between 0.15mm and 0.35mm depending on the geometry of the components used and the board technology. Its just a thermal break, with the spokes carrying the current...

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3. ## Re: Dimension Thermal Relief Pad

Thanks for your reply. I agree with you. I have to dimension the total width spokes in based the current.So the method In the IPC for me It is not complete. Normally i use an air gap of 0,5 mm for all. Why do you tell there is not air gap in inner layer ? For me there should be.

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4. ## Re: Dimension Thermal Relief Pad

All inner layers are flooded with epoxy, therefore there is no air gap.... It is a gap between the pad and the copper of the power plane.

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