PCB Calculator - who maintains that code?

Software
1

I’d like to chat with whoever maintains this code.

The STRIPLINE calculation is based on a single Er. This is only realizable if Er=1 (air). When constructing a pcb implementation, There is an Er of ~4 for the material below the copper. The Er above it is Er=1.

I’m likely the only person in the group who cares about this, but I’d like to see a change or option for different Er above and below the copper.

Thanks

2

I suspect that you are not, although I barely remember what a stripline is. Are you working over 500 MHz?

3

I may be misunderstanding you, but if you’re talking about a transmission line on a surface layer of the board, i.e. air above and ground plane on a layer below, wouldn’t you want to use a microstrip rather than a stripline? By definition, striplines have planes above and below.

But in general you should probably open a feature request here: Issues · KiCad · GitLab

4

I agree with the Sripline definition.

Consider another case: Microstrip, but with the addition of a conductive surface above the Microstrip. The rule of thumb is the top (or lid?) needs to be >3x the Height (H) dimension to be negligible. Suppose for shielding, this H distance is not possible, in which case, the Microstrip is more like a Stripline but with 2 Er values.

Hope this makes sense. The discussion needs a figure to go much further.

5

I see what you mean. Another related case is the microstrip with soldermask on top of the trace (feature request)

I’m not very familiar with the math behind these calculations or what assumptions get made in the approximations; it may be that the case you describe does not fit neatly into the models used in these calculators (or it may be that it works fine).

Whether or not the simplified model equations could be used here, another solution would be a FEM analysis. I understand there has been some development work in this area for future versions of KiCad which is exciting.

6

I’ve looked at several online calculators and none seem to handle this case. Would love to find a link to a tool implementing this feature.
I am making a gitlab issue.

7

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