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

On Wed, 11 Feb 2004 16:09:11 +0100, "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

Hi Massimo,

1mm X 1mm square would work quite well at 13MHz. So would 1M X 1M.

How well either works is wholly dependant upon what you intend to use
it for.

73's
Richard Clark, KB7QHC

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

"Dave Shrader" ha scritto nel messaggio
news:9qwWb.148648$U%5.678050@attbi_s03...
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

Thankx Dave, I'll try.

I know there are some pretty good PCB-capacitor aplets on the web.
Try a Google or similar search for them.

"RFSim99" is free for the downloading and has lots of tools, including
a component calculator that covers, among other components,
capacitors. It lets you just select FR4 dielectric (or any of several
others, or your specific relative dielectric constant), thickness, and
plate area, and will tell you the capacitance. Beware of fringing
effects, though, if your capacitor plate dimensions are not large
compared with the board thickness. RFSim99 doesn't do anything to
account for fringing as far as I can see. The capacitance is mainly
dependent on the plate area, but beware also of making one that is
long and narrow, because it will act like a transmission line. Also,
a problem with FR4 is that the dielectric constant is not well
controlled, so the capacitance may not be very consistent from
manufacturer to manufacturer.

Cheers,
Tom

"Massi" wrote in message ...
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

"Tom Bruhns" ha scritto nel messaggio
m...
I know there are some pretty good PCB-capacitor aplets on the web.
Try a Google or similar search for them.

"RFSim99" is free for the downloading and has lots of tools, including
a component calculator that covers, among other components,
capacitors. It lets you just select FR4 dielectric (or any of several
others, or your specific relative dielectric constant), thickness, and
plate area, and will tell you the capacitance. Beware of fringing
effects, though, if your capacitor plate dimensions are not large
compared with the board thickness. RFSim99 doesn't do anything to
account for fringing as far as I can see. The capacitance is mainly
dependent on the plate area, but beware also of making one that is
long and narrow, because it will act like a transmission line. Also,
a problem with FR4 is that the dielectric constant is not well
controlled, so the capacitance may not be very consistent from
manufacturer to manufacturer.

Fantastic, bellissimo, thankx
Massimo