sprial cst mws
Dear Helemish,
As you know, the smaller the minimum cell size, the smaller the "dt". Spiral inductors in ICs are usually very small compared to wavelength. Therefore both CST, which utilizes FIT, and FDTD tools need to use extremely small "dt" for calculating the transient fields for such cases, hence the too lengthy simulations.
One other thing to remember is that when importing GDS files for such structures from other tools like Cadense, normally they have a lot of even tinier features which further enforce smaller "dt".
Another EM tool that might help you is IE3D.
Cheers,