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Controlled Impedance Trace with ground fill

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TurboPC

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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.
 

flatulent

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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.
 

jzo777n

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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
 

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