I have written a program for simulating the temperature rise of PCBs. In short the program converts the pixels of a bitmap which represents conductors into a matrix of SPICE elements. The software needs LTspice for solving this matrix.
You can use the software to display the voltage drop of Power Planes.
It is possible to display the current density in conductors.
Based on the current density the copper losses are calculated. Finally the temperature rise can be simulated.
With this software it is easy to show the influence of copper weight, adjacent planes, dielectric thickness and other factors on temperature rise of the PCB.