Characteristic impedance of a trace on an inner layer between two reference planes. Works for symmetric and offset (asymmetric) stripline. It can also find the width for a target impedance.
Symmetric stripline. Wheeler's equation for a strip of finite thickness centred between two planes separated by b: Z0 = 30/√εr · ln{1 + 4/(πm) · [8/(πm) + √((8/(πm))² + 6.27)]}, with m the thickness-corrected width normalised to (b − t). It is accurate to about 0.5 %.
Offset stripline. A trace with dielectric h1 below and h2 above is treated as two symmetric striplines with plate spacings 2·h1 + t and 2·h2 + t in parallel: Z = 2·Z1·Z2 / (Z1 + Z2). This is the usual image approximation for offset striplines.
Derived values. The field is entirely inside the dielectric, so εeff = εr, and the delay per length is √εr/c.
Accuracy. Within 1 % of a 2D field solver and of the KiCad calculator for usual stackups. When the dielectrics above and below the trace differ (core and prepreg), use a weighted average εr.
A microstrip runs on an outer layer with one reference plane below and air or solder mask above. A stripline is buried between two planes, so it is better shielded and has no far-end crosstalk, but it is slower because all the field is in the dielectric.
The dielectric thickness from each face of the trace to the nearest plane. Your manufacturer's stackup lists the core and prepreg thicknesses. Subtract the copper thickness where the trace sits inside the prepreg.
Impedance of an outer-layer trace over a plane, with solder mask or embedded, and width for a target impedance.
Differential, odd, even and common-mode impedance of edge-coupled microstrip and stripline pairs.
Impedance of a coplanar waveguide, with or without a ground plane underneath (grounded CPW).
Width a trace needs for a current, or the current a trace can carry, with IPC-2152 and IPC-2221.
Current capacity, resistance, thermal resistance, capacitance and inductance of a plated via.
Thermal resistance of an array of vias under a pad, with fill options, and the temperature drop through the board.