1.5mm just happens to be 0.062" (1 / 16 ") which is the industry standard
board thickness.

Jim


"Jim" wrote in message
...
The application note for the NRF905 does specify FR4 board with 1.54mm
substrate thickness. FR4 is the board material used for almost all
printed
circuit boards, so you can use a regular board and just make sure the
thickness is 1.544mm.