Differentiate between mask and copper defined pads

[bpiphany]

I suddenly realized that a pad with a solid connection to a zone has a lot more copper area exposed (normally) than a pad connected only by a single/few traces. It doesn’t take too big a solder mask clearance to make the difference rather large.

I’m curious if or to what extent this affects how much solder paste should ideally be dispensed for those pads. Perhaps the solder is pulled strongly enough towards the pin and flows out extremely thin across the extra area and it doesn’t matter.

For simple and generic footprints like 0603’s and such it’s easy enough to have different footprints with either copper or mask defined pads. For generic IC packages where any combination of pins could connect to zones from part to part that would not be feasible. An option to automatically setting the solder mask opening equal to the copper definition in the footprint when the pad is connected to a zone seems like it would next to completely alleviate the issue.

Does anyone know if this is something that matters and people/manufacturers care about.

[eelik]

I would say it doesn’t matter with 0402 and larger pads if other aspects are OK, but it may be important for 0201 size.

It may be worth noticing that in the official KiCad libraries, in the development version at least, 0201 resistor footprint has specialized paste pads while in 0402 it follows the copper pad.