I'm working on an open source filter design where the PCB can be reused for many future designs. It is based around a Sallen-key filter since a few changes to the capacitors and resistors can change it from a low-pass to a band-pass or a high-pass. When looking at layout, I've realized it would be very beneficial to make the capacitor and resistor pads fit both larger (like tantalum caps) to smaller 0402 packages.
Is there anything I should be careful of while designing this 'universal pad'? Is it possible someone has built something like this already?
Best Answer
Assumption 01: the board is intended for hand assembly, tabletop experiments and hacking. Assumption 02: the frequencies are low (say, under 1MHz)
In that case, I would make the passive pads 3216 (tantalum size A) or 3528 (tantalum size B). If you are planning to have pads for a large tantalum cap, then having small 0402 ceramic capacitors doesn't give an advantage, because the large pads for the tantalum cap are there anyways. Size A or B can comfortably accept 0805 and 1206 passives.
P.S.
3216 comes from metric 3.2 x 1.6mm.
1206 comes from imperial 0.12 x 0.06 inch
They are pretty much identical, if you convert from inches to mm.