Cb = K1*(er*eo*Thickness*length)/spacing.
Co = K2*eo*thickness*length/spacing

er = relative permitivity of board material
K1 = percentage of E field in dielectric material ~ 30% - 40%
K2 = percentage of E field in air ~ 70% - 60%
eo = relative permitivity of air
thickness = thickness of copper cladding
length = length of parallel paths
spacing = spacing between parallel paths.

Note: there are two capacitors in a single layer PCB. The path through
air and the path through the board material. You sum the total of both
capacitances.

er for most boards is between 2 and 4.

Design your initial capacitor on a sample board and refine the K1, K2
and er terms.

DD

Massi wrote:
Hi to everybody,
I need to obtain a capacitor in a PCB single sided. Does anybody has a
formula to calculate the lenght, the width and the shape of it?
I'm working around 13 MHz (=13000000 Hz...)
Thanks

Massimo