Controlled Impedance Trace with ground fill

Status
Not open for further replies.

TurboPC

Advanced Member level 4
Joined
Mar 14, 2002
Messages
112
Helped
15
Reputation
30
Reaction score
15
Trophy points
1,298
Activity points
1,155
how do i make controlled impedance trace

I have a 6 layer-board with 10-mil spacing layers and FR4 material. My 50-Ohm trace is on component side and the ground layer is the next layer (10-mil distance).

Using the formulas, I found that the trace should be around 17 mils thick to obtain the 50-ohm controlled impedance.

For EMI reasons, I did a ground fill on the component side but I kept a clearance around the controlled impedance trace to avoid affecting the controlled impedance.

What should be this clearance? Some say 3 times the trace width. Some say 3 times the "ground plane to trace" distance. What do you think?

Best regards, T.
 

controlled impedance traces

Appcad which can be downloaded from http://www.hp.woodshot.com/ has a coplanar transmission line with ground plane under it calculator that you can use to make the calculations.
 

I think that you refer to the rule of thumb for crosstalk, 3 times ground plane to trace distance
This is a formula for crosstalk between parallel lines from by Dr. Howard Johnson, http://www.sigcon.com .
The worst case value of the coefficient of coupling K (i.e., the crosstalk coefficient) is approximately:

K = 1 / (1 + (D/H)^^2)

Where D is the separation between the centerlines of the traces, and where H is the effective height above the nearest reference plane.

But I think that you must use a field solver for a more correct answer


jzo
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…