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Footprint Rule of Thumb?

I making footprints for a project and outside of the typical 0603, 0805, etc I'm running into a lot of datasheets that don't have recommended footprints! Our company works in mils and I'm wondering what people usually use for through hole and surface mount tolerances.

As in, if I have a part that has a 50 x 50 mil suface mount contact what should I make the pad be? Can I just make it a 60 x 60 pad with a 70 x 70 solder mask?

This also comes into play with through hole parts. The datasheet may say it's a 30 mil diameter cap lead for instance but then what should I set the drill size, pad size, and thermal relief size? Also the default internal layer size?

Is there an online website calculator peopel use for this or some good rules of thumb? It seems the default Allegro library doesn't have a lot of footprints and pad sizes I need for my design.

Any help is appreciated!

steve over 11 years ago

Best to follow the IPC standard IPC 7351 B. Take a look at PCBLibraries for a lite (free) and paid for version that generates footprints using this standard.
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