I’m hoping someone with more experience with SAMD21’s (Pro RF – I’m testing LoRaWAN) can offer suggestions about how to mount them for prototyping and deployment.
Initially, for development, I’ll use standard breadboard; for deployment I’ll wirewrap onto perfboard.
For my initial testing, I have my SAMD21’s “pinned” to breadboards with header pins through the right side signal pins (but not soldered): all ground pins (left and right) and left signal pins are empty. I need to expose the signal and ground pins for connecting and to stabilize the SAMD’s on the boards for prototyping and then deployment. So I want to solder headers onto the SAMD that will let me prototype now and wirewrap later, but I want to do that soldering only once – I’ll be lucky if I don’t screw them up trying to solder them once: twice would surely be a disaster. 
My initial thought was to use male-male headers: short pin up through the bottom of the board and soldered in; longer pins then into breadboard for development and through perfboard holes for wirewrapping. I’d use something like the Sparkfun PRT-00116 for headers and PRT-13268 or PRT-12070 for perfboard.
Because the SAMD21 board has signal on the inside rows and ground on the outside rows, on both sides, I can’t use a standard 2x10 header on each side – plugged into breadboard, the signal pins would all be grounded. And using two PRT-00116’s on each side would cause the same problem.
The alternative I thought of was to use PRT-00116’s on the two rows of signal pins, then find similar headers with shorter pins to use for the grounding rows. If the lengths worked out right (!), the signal pins would sit in breadboard sockets and the grounding pins would not make contact (but could be connected to with a female-male jumper to connect to breadboard ground).
For deployment, pull the SAMD21 board out of breadboard and insert into perfboard, and all signal and ground pins would be available for wirewrap.
But before I order headers (if I can even find ones that would work) and pick up my soldering iron, I thought I’d see what others might have done. Or am I unusual in wanting both breadboard and perfboard mounting options?
Any ideas welcome.
David