[SOLVED] X band Power amplifier heat sink requirement.

[shashy.br]

Hi all ,


I am suing a X band power amplifier from HITTITE (HMC952LP5GE) , the dissipation i encounter from the device is 9 W ,

The application is for a CW operation and i needed to know if any heat sink is required for this amplifier.

i plan to do 6 layer board in which other components are also present ,

will providing excess number of vias nearby the component in the PCB be sufficient for this power dissipation?

 

[jiripolivka]

You should follow manufacturer's recommendation for cooling.
If you use the MMIC as a die, then the case should be made of copper and an external heat sink attached.
If the MMIC is encapsulated, try to get an evaluation board from Hittite to see how they do the cooling.
When I used power MMICs from RFMD tc., I used small modules, 0.7" x 1.25" made of brass 20-mil sheet to which I soldered the ground pads of the MMICs. Only active pins were connected to a microstrip 50-Ohm line or DC islets as needed.
My modules were then mounted in aluminum milled cases. Such solution offered an excellent grounding and heat-sinking. My designs usually behaved better than MMIC specifications due to that no via holes were needed.

Sinking nine watts is a huge task for a tiny MMIC. Do your best!

 

[tony_lth]

When I used power MMICs from RFMD tc., I used small modules, 0.7" x 1.25" made of brass 20-mil sheet to which I soldered the ground pads of the MMICs. Only active pins were connected to a microstrip 50-Ohm line or DC islets as needed.

I can't image it,can you paste a picture if possible? Thank you.

 

[shashy.br]

jiripolivka please paste a picture if possible....i need a clearer idea for the same.

Also let me know if adding sufficient number of via's near by the IC and the ground Pad of the IC itself , and also adding two mounting holes to the proximity of the IC ..can the heat be dissipated ?

I also plan to place an indium sheet below the PCB( directly below the IC) so that there will be more heat transfer from the PCB to the mechanical enclosure..!!!

 

[jiripolivka]

jiripolivka please paste a picture if possible....i need a clearer idea for the same.

Also let me know if adding sufficient number of via's near by the IC and the ground Pad of the IC itself , and also adding two mounting holes to the proximity of the IC ..can the heat be dissipated ?

I also plan to place an indium sheet below the PCB( directly below the IC) so that there will be more heat transfer from the PCB to the mechanical enclosure..!!!

I have no picture at hand. Can you, please, use a pencil to draw a rectangle I indicated,and cut such rectangle from a 0.020" sheet? Solder the MMIC by its ground pads to it, and use 50-Ohm stripline sections as needed under the "live" pads. For DC and control pads, use similar stripline material squares. That's all, and it works. I used four 0-80 screws in corners to secure such modules in aluminum cases, and interconnects were made with ~50-mil wide strips of 5-mil sheet. Fine up o ~10 GHz. Indium padding can help in heat-sinking but I would prefer soldering in a copper-block case.

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You also can use a thin layer of a silver Epoxy to improve ground connection and heat transfer.

 

[tony_lth]

Thanks, jiripolivka

 

[shashy.br]

Thanks for the reply