I am in the process of designing a PCB that has 6 layers, here are the details:
- Desigining for 50R signal, only one area of PCB is required for 50R.
- Freq. range 0.9GHz - 1.6GHz.
- 6 layer board with dielectric constant of each layer being the same.
- 1oz (35μm) copper on each layer.
- RF signal to be routed on top layer, GND layer to be chosen to optimise trace width.
At present going from Layer 1 to Layer 2 (see stackup image below), I get a trace width of approx 0.22mm.
QUESTION(1): If I were to cut a region out of layer 2 so that the GND plane for the RF circuit on the top layer became layer 3, can I assume the dielectric constant to still be 4.1 if both core/prepreg have Er = 4.1? And therefore I just increase the 'h' value in the equation for trace width?
QUESTION(2): Do I need to factor in anything relating to the missing copper on the inner layers or can I consider that the board will be made such that there is no air gap?
QUESTION(3): If the Er was different in between layers, how would that be dealt with?