Footprint election

Question

I have to do a PCB and I have seen that the datasheet of some discrete component like microcontrollers indicate what footprint to use, but when I want to choose the footprint of a capacitor or resistor I have multiple choices which seem to be right.

I mean, for example, if I need a 1μF whith 0603 dimensions, I may choose either SM0603 or SM0603_Capa or SM0603_Resistor. I suppose that SM0603_Resistor is for resistors, but there are still two options and it looks like both are rights or at least people uses both.

So, how do I know to choose footprints?

Answer 1

The ideal footprint doesn't just depend on the package size. You should also consider:

• The height of the contacts on the part (not all "A size" capacitors are the same, for example)

• The mass of the part

• Whether you're doing reflow or wave soldering.

• For reflow, The thickness of the stencil you'll use.

• How much you're willing to trade off assembly defects and reworkability to cram more parts on your board.

So whatever footprints are provided by Altium, they're not likely to be ideal for your design. (And you also shouldn't just blindly trust the footprints provided by the part manufacturer --- they'll give you a good compromise footprint, but not necessarily the best one considering all the details of your design)

But if you're doing hand assembly in low volume, you can probably get away without having the absolute "ideal" footprint. And the provided libraries (at least for common two-terminal devices) are probably acceptable, whichever one you choose.