I see what you are pointing to here. But why do you want to apply concentrated heat flux to the face? The reason I am asking is that normally concentrated heat flux is applied to each node of the face and depending on the how your elements are distributed over this face, the heat distribution changes.
I think in this case you may need to apply a volume heat flux to your component. As you know the volume of your component from CAD, you can divide the heat flux with this value to get the exact volume heat flux that needs to be applied. Alternatively, if you are not interested in the heating of component itself, you can simply remove it and instead make a exact face cutout over PCB and apply surface heat flux instead on that cutout. Make sure to divide the total heat flux with the surface area of the cutout.
You can have a look at this example for more info.:
(Please note that this is a thermomechanical analysis but will give you the idea how volume heat flux is applied)
For surface heat flux, please see here:
If you have any question/s, feel free to ask.