I have been asked to calculate the trace impedance of some routing, I know that impedance is dependent on the Er, trace thickness, trace width and distance from a plane. But the trace changes width as it is routed. And the two different impedance solvers have provided 2 different answers. In Altium I have impedances of 34.98633726, 32.81547534 and 28.78596208 for traces of 0.305, 0.33 and 0.381mm. But The Saturn PCB Toolkit shows 45.2196, 43.2286 and 39.6915 respectively!
- How do I work out the overall impedance of this trace?
- Which is the better result?
TraceHeight is 0.05mm
TraceToPlaneDistance is 0.142mm
Er is 4.2
TraceWidths are 0.305mm, 0.33mm and 0.381mm along a single trace (the default should be 0.381mm but there are fine pitch devices nearby and a reduction is required to get the trace into the pad).