The 3-pin TO-220 (and other power packages) often have an internal electrical connection from the thermal tab, to the center pin. I typically extend the pad for the center pin into the pad for the thermal tab, making them a single pad as far as KiCAD is concerned. While I’m at it, I may add a bunch of thru-hole pads inside the thermal-tab pad, for connecting to a back-side copper pour serving as a heatsink.
(You may need to remove your shoes to count all the instances of “Pad 2” on this footprint. Click on the image to see the whole thing:
From experience I know debating design practice is a minefield and I want to point out that I am absolutely not trying to put my way of doing things above others, we just have developed different ways of doing things. And please keep in mind that I am not a native English speaker so if the way I express myself can be interpreted as rude or arrogant it is completely unintentional.
With that out of the way…
Neither of these examples would be an issue to me because I would not design the footprints like that. I hope by saying that I can make my case for making same net clearance check optional. I think it is unfortunate that KiCad have this unnecessary limitation while having such powerful tools as push and shove, diff.pair and length matching.
I have very high hopes for KiCad and crossing my thumbs that the design rule options will evolve and be as great as the current features. Advanced design rules is a very powerful and sought after feature that other CAD tool vendors reserve for their high end products or as silly expensive addons.
For the TO-220, I would use four pins, separated, and for the PQFP I would go width a single thermal pad with negative soldermask clearance. Neither would have thermal vias in the footprint.
I am a new user and have just done a few footprints yet so it is possible I am missing something.
No, I want to have full control over via placement so I can modify their position at any time. The mechanic designer is inevitably going to move something on top of it in the last minute. I forgot about the via stitch issue though.
I heard that version 5 might include via stitching. This might enable me to do it your way. (But until such time i need at least the option to ignore these drc errors.)
Also how should vias within pads (or near pads) be handled? (Not tended vias also have a hole in the solder mask.)
(I don’t like the eagle way that all of them are errors. This masks real errors. Having lot of false positives in one pcb leads to potentially ignoring the correctly flagged problems.)
If I understand you correctly you mean manually placed thermal via in pad? I think via in pad should/must be accepted in that case. In the long run though, I hope there will be options for via in pad or not. For me, ideally I would like to have the options:
Via to pad - pad to via annular ring
Via to drill - accepts annular ring overlap but no drill in pad
And be able to set up the rules per net basis, layer and so on. I know this is a lot of work reserved for the future but are the kind of features I allow myself to dream about.
