> Somehow guarantee that Vss connects first - then what ?

What are you using to connect the daughterboards?

SIP or DIP headers could be used; if the number of pins
is low, it wouldn'd be too much trouble at all to grind a
few mm off of the data pins so that the Vss pin is longer.

Of course, not a production level solution, but if this is
just for home consumption, it would probably do okay.

Easier and less real estate than card-edge, too.

Mike H.
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