Is there a “rule of thumb” of the pad size verses the hole size?
I usually keep a ring of 0.3mm around the hole. So if you have a 1mm drill, draw a 1.6mm pad.
On tight designs, you may especially for vias use a smaller width. I would feel good with a 0.2mm ring. If in doubt, look for the design rules of your board house.
Yes there is,
Have a look at IPC-2222 and IPC-2221
BASICALLY: Pad Diameter = Minimum Hole Size + Minimum Annular Ring X 2 + Minimum Fabrication Allowance
According to IPC-2221 the Minimum Fabrication Allowance is 0.6mm for Level A, 0.5mm for Level B and 0.4mm for Level C.
There is a lower limit. Manufacturers require an annular ring of 0.13 to 0.2mm
Pad size vs hole size depends on current requirement. I usually use annular ring about 1/4 to 1/2 from diameter of component lead size.
Also the distance from near pad needs to be considered (by voltage between pads). To near can make currents “jump”.
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