Hello, newbie here and would like to get a better understanding of choosing Pad Clearance values. I started my project with my Power pad to have a clearance of 0.3mm.
Here is a view of my board.
There is overlap on the pads.
Here is a design I found:
There is no overlap.
In my design should I change my global power to 0.2mm Clearance and the Track Width to 0.2mm. Or should I just adjust the pad Clearance number?
Any comments on what is the rule of thumb?
Thank you
Enforcing clearance is used for two purposes:
(1) To make sure the PCB manufacturer can produce the board. Generally, 6mil is possible with the standard process these days, smaller features quickly become more expensive.
(2) If you have high voltages / sensitive traces on your board, such tracks need wide clearance.
Unless you power net is high voltage, there is no reason to give it more clearance than everything else.
If +5VA means +5V than I don’t see a reason to have bigger clearance than 0.2mm for it. But if 5VA means 5W (W=V*A) from PoE (so about 50V and 0.1A) than I would use bigger clearance and make it smaller only where it have to be.
With KiCad 4.0.7 I have made some experiments and found that through 0.6mm gap I can’t go with 0.2mm track when I have 0.2mm clearance. So I decided to use 0.199 mm clearance. Didn’t checked if it is still needed in V5 - I continue to use 0.199.
Thank you for responding to my post. +5VA is only +5V. I went ahead and changed the clearance to .2 and I was able to route the board.
Thank you
Thank you very much.
There are some other considerations for clearance.
These are for matched impedance tracks such as differential pairs, and sometimes (for example analog high frequency stuff) you just want some bigger clearance to lower overall capacitance and therefore coupling between different tracks.
But for simple beginner projects these generally are not very relevant.
You specifically mentioned the pad clearance. Using thinner tracks does not change the clearance between pads themselves, but it does increase the clearance between a pad and a track. Doing this is not a proper way to meet certain goals though. The interactive router frequently moves tracks around and pushes them aside to make room for “other stuff”, and while doing so it only regards the actual clearance settings of the tracks and pads.
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