Tips on creating combo footprint with copper wires?

I need a footprint for a PNP pair where I’m not sure if I’m gonna use two matched TO-92’s or an smd dual package. It’s about matching for an expo converter for an analog synth.

I just started by taking SOT−363 and TO-92’s and copied into a new footprint and renamed the pads:

But then comes the question about connections - should I just use graphic lines on copper layer or should I make polygon pads? Will I hit issues down the line if I just use graphic lines?

Why not place both options explicitly in the schematic and pcb side and set one of them as DNP in the bom? This would ensure that anybody reading your schematic/pcb will know what you where doing including you in 5 years.

Why not place both options explicitly in the schematic

I think that would be rather messy in the schematic?

Well your whole solution is messy. so why not make it completely obvious in the schematic?

Well your whole solution is messy.


This is for an old schematic design that I’m using for analog synths. I’m actually somewhat keen to keep the schematics intact and have even explicitly annotated to match the original. That so I can use forums for these designs and talk about things like R3, Q1 if (or when really) I need to troubleshoot :slight_smile:

I’d really like to keep the schematic as is and just make a footprint where I can either populate an smd dual or two matched TO-92’s. I’m pretty sure I’ve seen other PCB’s do combos like that before…? Maybe they did explicitly in the schematic, I don’t know…

Also seemed like a fun thing to do, I’m all about learning :blush:

Well give the alternative parts a reference outside the range of the ones normally used (example add a prefix letter like QA1 or add a number prefix/suffix)

Of course you can bodge it on the pcb side but future you will pay the price for it. (The clean way is what i suggest. You can do it your way but that will make your life harder in future. And i doubt it makes life easy now to be honest.)

If you still want to use the bodge on the footprint side then give the pads that need to be connected the same pad number. That way pcb_new will want them to be connected and you can use normal traces to do it on the pcb side.

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Yeah, it’s a monster, I couldn’t help myself. Can’t decide about 2xTO-92, 2xSOT-23 or SOT-363:

Thing is there needs to be a 3300 ppm PTC resistor in thermal contact… I think this layout will support that well for all three package types.

That’s like saying “RIP in peace” - redundant.

Relax and put on a CD disc :I

There, I fixed it.


Just to be sure, also add TO-3 and TO220 footprints.

For long-tailed pairs or other circuits where tempature differences between transistors are important, using TO-92 is not a very good option, (Neither is SOT-23).

With TO-92 there is a lot of insulating epoxy between the dies, and even if you wrap some copper wire around bouth packages the coupling is not very great.
You can easily get different temperatures bedause of heat conducted through the pins. Power transistors with a metal backside can have much better thermal coupling between them.

In KiCad you can add “custom graphics” to a pad. You’ll need to do a bit of experimenting to get the details right though.

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