Effective Thermal Conductivity of Multi-layered PCB
 

Hi everyone,
I work as a thermal design engineer for aircraft and EW applications. and we usually work with multilayered PCB like fr4, rogers etc.

My question
1. is there any hand calculations that thermal design engineers use to get the rough estimate of the effective thermal conductivity of such PCB.
i usually use parallel and series formulae for calculation of effective thermal conductivity. but the results are way off to the practical values i get when being calculated in the software ( i use flotherm XT)

2. How do you model vias under the PCB for doing thermal simulation as the vias will take a lot of time for both to model and simulate.

Hi Karnataka,

1. Yes, series and parallel connection of the layers should work for calculating rough values. Of course, you need to use the right area percentage per copper layer. For more detailed simulations you need to spatially resolve the conductivities on the PCB.

2. Also for vias you could calculate effective thermal conductivities for example from the thermal resistance. Then replace the via array in your model by a solid body and assign the effective values to it.

What are the values you calculated and what do you expect from Flotherm?

Regards, Florian