How to flash nrf51822 WLSCP chip

Question

Is there any recommended way to flash the nRF51822-CEAA-R WLCSP chip? 
 
 Should a PCB design have UART design for flashing the nRF51822 chip after it is soldered on? Or should the chip be flashed and pre-programmed on a development board before being soldered onto PCB?

AmbystomaLabs · Accepted Answer

All nRF devices are programmed initially via SWD not UART. 
 You can choose to have your own version of firmware with a UART bootloader designed for factory flashing, but that is not the normal process for most people. 
 Many, many companies offer chip programming services. Just google it. This way you could have pre-programmed devices on tape and reel for placement by your CM. 
 You implied that WLCSP devices can be placed, programmed, pulled and placed again. WLCSP devices just like BGA devices cannot be placed on a board, programmed, then removed and placed on a second board. The solder balls are one hit wonders and can only be placed once. Any success at placing them a second time is just plain good luck but is not expected of the design. 
 Programmers for WLCSP and BGA use a zif like connector with pogo pins or sprung contacts that contact the device for programming. That is how they get programmed before pick and place. 
 Most everyone places blank chips then builds some sort of jig to do programming via SWD and functional testing after they get boards back from the CM.