50 ohms in multilayer board

[brmadhukar]

Hi,
What is the correct approach to do a 50 ohm track on a layered PCB with the second layer ground?
a) take the height to be the layer height (not of PCB) and calculate track width? This gives very small impractical values.
b) Do not fill any copper between top and bottom layers.
TIA
BRM

 

[Mazz]

It is not absolutely true that microstrips are impratical, thay are largely used and depends on PCB height and dielectric constant. In order to have more degrees of freedom in chioce of the track width and spacing you could also use the coplanar with ground structure:
gnd ---------------- ---- ---------------------- gnd
gnd ----------------------------------------------- gnd

Mazz

 

[jon2000]

It is very common to clean the copper below the 50ohm trace. For example, 50ohm trace on the top (layer 1), clean the copper on layer 2 just below the trace (not necessary for the whole layer), and make layer 3 as ground. It will result a wider trace which will give lower loss.

 

[brmadhukar]

Hi,
Are there any examples ( brd files or gerber files) of this. Or does some one address this in any book.
TIA

 

[shaw]

You can refer to the simulation software CITS or appcad