About impedance calculation with Saturn PCB Toolkit

[michaelchang]

Hello,

I am doing impedance calculation with Saturn PCB Toolkit. I have two questions.

At first, I used "Microstrip" for all the tracks on outer layers, and selected "plating thickness" options. Then, I did some research trying to find the difference between "embedded microstrip" and "stripline". I found that: copper trace on the surface of PCB, which is covered by solder mask layer should be regarded as embedded microstrip. If it is true, does that mean I should use "Microstrip Embed" to calculate all the tracks on top and bottom layer? (Previously, I thought "Microstrip Embed" is only used for those signals on the 2nd layer, and the top layer is not a plane)

My another question is: my inner signal layer is between a power layer and a GND plane, is it OK to use "Stripline Asym" to calculate the impedance. In other words, in "Stripline" structure, is it necessary to make the signal layer between two GND layers? Can I place a signal layer between one GND layer and one power layer, and still use "Stripline Asym" to calculate its impedance?

Thank you!

[robertferanec]

1) I use microstrip. It doesn't really matter, the exact values needs to come from PCB manufacturer anyway. Saturn PCB only give approximate numbers.

2) I often use "Stripline Asym". "Stripline" has same H which is very rarely the case of stackups which I use. For "Stripline Asym" I can use different distance between signal layer and reference plane above the signal layer and I can use different distance between signal layer and reference plane below the signal layer. GND is usally good reference plane, power plane can be also reference plane, but not always. For example, a 3V3 power plane with many decoupling capacitors can be a reference plane (decoupling capacitors are short circuit for high frequencies, so for high frequencies 3V3 plane with many decoupling capacitors can be almost as a GND). However for example a 12V input voltage power plane in many cases may not be a good reference plane. I am not sure if this answers your question.