KiCad Schematic - dealing with Servo Motor Controllers

Hi all, new-old kid on the block here, coming back to electronics after 20 years or so - please be gentle! :slight_smile:

I’m trying to draw up an existing board that uses five HEROIC HR4982 servo motor controllers. These come in TSSOP-24 packages but as with several other servo motor controllers (e.g. TMC2130) they have an exposed metal pad on the underside that’s meant to be soldered to the board and then four or nine thermal vias are used to conduct heat to the heat sink which lives on the other side of the board.

I created a Symbol for this which has all 25 pins (25 being the pad, see attached image) but when I use Update PCB I get errors such as:

Error: Component D6 pad 25 not found in footprint Package_SO_TSSOP-24_4.4x7.8mm_P0.65mm

Is there a TSSOP24 package variant that would have the thermal pad already or should I just copy-create a new one?

Never mind, solved.

I was getting frustrated trying to add a new footprint because “Create new library and save current footprint” didn’t work like I expected. It created a new library folder and saved the footprint to disk, but didn’t add it to the Project Specific Libraries so the new footprint wasn’t visible anywhere.

Kudos to Creating a Custom KiCad Footprint Library for giving me the clue that I had to add new footprint libraries manually.

I cloned TSSOP-24_4.4x7.8mm_P0.65mm, added a 2.85x4.05mm pad for pin 25 in the middle of the package and updated the symbol to use that TSSOP-25 footprint. Then I had to re-add the five 4982’s to the schematic, because… (?)

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There seems to be a HTSSOP-24-1EP in the library - it looks almost similar to TSSOP-24, but with the EP. Maybe that would work?

if you assign new footprints with cvpcb you should not have to delete/re-add parts in schematic?


@Anders_Wallin Thanks, that would probably work.

I can’t find that item in my local Package_SO library, which only has 174 items. I can see it’s in the Github Package_SO library, which has 190 items. Now to figure out how to update…

As soon as a symbol is added to a schematic it’s pretty much decoupled from the library in regards to anything that is linked via fields like value, reference, datasheet, footprint, etc. as those are seen as customized settings that are different from one schematic to the other and even from one symbol copy to the other, that you add from the symbol library.
If you change the graphical appearance or pins of the symbol in the library, then those changes make it right through to the schematic copies though.

The reason for this IMHO must be because how KiCAD worked in the past and still works (symbols and footprints are not seen as a single part, you can work like that, but KiCAD doesn’t force this, just enables it), so the link between the symbols in the library and the footprints are VERY flexible.
This allows on the fly changes from one footprint to another for the same symbol.

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