You need more pins but for those who need 3…
I took 2x2 1,27mm pin header footprint. Deleted one pad. 3 left I shifted very little outside. Such 3 pin connector we use for debug and programming.
For debug we solder into it 2x2 pin header (with one pin removed) and use 2x2 socket to connect programmer/debugger with it.
For production programming we use 3 pins from 2x2 header just temporary inserted into these 3 holes. Thanks to holes being little shift this get enough good contact for few seconds needed for programming.
Thanks to having only 3 pins you can’t insert this pin-header wrongly.
You can see this solution (on the left) in PCB I showed here long ago:
1 Like