Doh!

[Kasper]

For protototyping with castellated modules, assuming no ground pad is needed, then I a stick a piece of card under the module and hand solder them. The gap left by the piece of card makes it possible to remove the module using a solder sucker, after I have blown it up... again.

Good idea. I'm going to try that.

For a wroom module, I found it helpful to put a large hole in the centre ground pad.

If the hole is larger than your soldering iron tip then it gives access for soldering and inspection.