What's the mechanism for the copper loss decreasing as the board gets
thicker? Of course, if you assume that the traces consist only of
microstrip or stripline transmission lines with some fixed impedance,
then the line width will be greater on the thicker material, resulting
in lower loss. Is that the rationale, or is there some other phenomenon
at work?

Roy Lewallen, W7EL

Rick Karlquist N6RK wrote:
"Roy Lewallen" wrote in message
...

Loss will be greater on the thicker board, because a greater fraction of
the fields surrounding traces and components will be in the board
material as opposed to being in the air. Having less field in the board


This is correct as far as dielectric loss is concerned, but copper resistive
loss decreases as the board gets thicker. Which one will dominate depends
on frequency and characteristic impedance. At low frequencies, dielectric
loss will probably dominate. At high enough frequencies,
copper loss will dominate. For low enough impedance traces, the
field will be mostly in the air for either board thickness. Complex
problem to analyze.

Rick N6RK

If you keep the impedance constant, the loss goes down
for the simple reason you state that the width increases.
If you keep the width the same, the loss also goes down
because the characteristic impedance is higher. This is
because the copper resistance, relative the the characteristic
impedance, is lower. This is analogous to open wire line.
Suppose you make two OWL's with #14 wire. Suppose
one line has 1/2 inch spacing and the other has 1 inch
spacing. The 1 inch line will be lower loss owing to its
higher characterisitic impedance. OTOH, a #14 twisted
pair will be much higher loss due to its much lower impedance.

Rick N6RK

"Roy Lewallen" wrote in message
...
What's the mechanism for the copper loss decreasing as the board gets
thicker? Of course, if you assume that the traces consist only of
microstrip or stripline transmission lines with some fixed impedance,
then the line width will be greater on the thicker material, resulting
in lower loss. Is that the rationale, or is there some other phenomenon
at work?

Roy Lewallen, W7EL