Creation of thermal via in cfd

[Anonymous]

I am trying to use thermal via to determine if I would be able to cool off my part on the pcb. I am ruNing into problems because I do not know the best way to model vias. I created 120 by 120 array of vias between the part and board. These were through vias and used CTM to predict junction temp on the board. I guess my question is very basic what is the best way to create vias.. I went through a few places for help in cfd tutorial but could not find too much information could you please advise?

[marwan_azzam]

Hello Sulman,

I would think placing a physical array of 120 by 120 little rods is not an efficient way to model the thermal vias.

I suggest you try replacing the array with one solid part and use orthotropic material properties to represent the conduction in the direction of the heat flow.

[Anonymous]

Marwa,

Thanks for the reply. I am not too clear on this. So the pwb will have its own thermal conductivity which essentially is orthotropic without vias. Would I then need to create another solid and embed that solid within the pwb? Or are you saying that use the existing material as "pwb material" and just change my thermal conductivity normal to the pwb due to the presence of vias. If so how does cfd differentiate between having just vias in a localized area under a component in comparison to vias being spread out in the pwb? Appreciate your feedback

[Anonymous]

Marwa,

The other part of this is that if I do create an orthotropic material how would I be estimating percentage copper due to vias and percent laminate. Also would this technique lead to under predicting temperature if you copper proportion and laminate proportion is not correct?

[Jon.Wilde]

Hi,

You could use either approach here. Marwan's is the ideal solution to run with though, so you can run faster and optimise your design.

If you would like to check you have the correct material settings, run a test 🙂

Set up a super simple model and compare with vias and without, then you can feel more confident that your new, simplified replacement material is defined just as you need it.

Does that give you enough to get going with?

Thanks,

Jon

[Anonymous]

Thanks Jon yes the approach did help! I tried modeling it the way you suggested and the results were reasonable.

Thanks,

S.M

[Jon.Wilde]

Thanks for letting us know! Please do mark whatever provided you with a solution as 'accepted solution' 🙂

This way, it will be right at the top for others to find.

Thanks again!

Jon