I am working on matching an antenna to the nrf52832 QFN package. I am looking at the reference design, which has a 30 mil wide trace. I believe that is supposed to be 50 ohms. However, when I look at the design files in Altium (nrf52832_qfaa), it says that the board is 63 mil thick FR4 with a dielectric constant of 4.8. But, a 30 mil wide trace on 63 mil FR4 with a dielectric constant of 4.8 yields an impedance of about 92 ohms. To get 50 ohms with a 30 mil line width, you need a board thickness of about 17.5 mils.
What is the actual board thickness for the reference design?
We use coplanar waveguides as transmission lines. For coplanar waveguides 50 ohm tracks are 0.72 mm(30 mil) wide on a 1.6 mm FR4 Board.