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THS3091: Cooling for PCBs

Part Number: THS3091

Hi!

I have a question about cooling PCBs. And I am very unexperienced with this.

I am building a low-noise RF amplifier by using several THS3091 in parallel and bridge configuration to achieve up to 2.5 W into 50 Ohms. I also would like to put the circuit into a grounded aluminum enclosure for RF shielding.

The heat of the op-amps is sunk into the PCB ground plane. And the heat of the (linear) voltage regulators is sunk into the PCB power planes.

Should I attach the PCB to the enclosure and attach a heatsink to the enclosure from the outside?

What would you recommend to attach the PCB to the enclosure with good thermal connection but also provide electrical isolation to the power planes?

(1) Leave the solder mask and use thermal epoxy / thermal paste??

(2) Remove solder mask and use an electrically isolating thermal pad??

(3) Remove solder mask and use electrically isolating thermal epoxy / thermal paste??

(4) Something better than the above??

Can you recommend certain part numbers for thermal epoxy / paste / pad??

Thank you so much!!!

  • Hi Niklas,

    do we talk about such an aluminium enclosure?

    www.gquipment.com/index.php

    This sort of enlcosure would be ideal as it allows the ground plane a large area contact to the enclosure. Usually no additional heatsink is needed then, because the enclosure itself plays the role of a heat sink.

    If you have the heated supply planes routed over a ground plane and they share a large common area, the whole PCB is warmed up by the heat of the regulators and the PCB can be cooled via the ground plane contact to the enclosure. This would usually be enough.

    If you have huge heat to dissipate in the regulators it could be wise to have pre-regulation outside of the board. This would decrease the heat the whole PCB has to dissipate.

    Kai
  • Hi Kai!

    Thank you very much! You reply is very helpful!!!

    Best regards

  • Hi!

    I have another question. For the THS3091 it is important to remove the GND plane under sensitive pins/pads (like the output pin).

    If we now attach the PCB flush with the grounded enclosure, do we so-to-speak reintroduce a continuous ground plane under the op-amp?

    Thank you!
  • Hi Niklas,

    it does not harm, if there's a distance of let's say at least 5mm between PCB and enlcosure. In my designs I do often have a solid ground plane in the bottom layer while having the ground plane removed in the second and third layer of a 4-layer PCB. It depends a bit on your circuit, the used HF-OPAmps, the cabling, etc. what's useful and what's not. If you feel unsure, increase the distance.

    Kai