Tony Koryban Mail Bag Archives: Attaching a heat sink to an RF amplifier properly

Heat sink attachment is as important as the heat sink itself.  That’s one reason why ATS invented maxiGRIP and superGRIP heat sink attachment.  But what about RF devices?  Well, Tony Koryban got just such a question in his mailbag:

Dear Doggone Thermal Guy,?

I have an RF amplifier device which operates fairly inefficiently. Only about 1/3 of the power it takes in goes out as RF . The rest is dissipated as heat (5 watts).?? The figure below shows an arrangement recommended by the RF amplifier vendor to insure that the chip is well-connected to the heat sink. The heat sink is mounted on the side of the board opposite the device. To get an adequate thermal path, the vendor recommends a “pedestal” or pin, which is press fit into the sink, and soldered to the backside of the device (the device has a metal backside plate for this purpose).?

Some of our circuit designers have tried this approach, but using a “solder plug” instead of a pin/pedestal.? This seems to work, but our manufacturing group says it is hard to manufacture. I can see why, since it must take a bit of work to fill a 1/8 inch diameter hole full of solder.? Other designers say that simply stitching the front and back planes of the circuit with a dense pack of vias will be enough.?

Do you have any recommendations? We want to make sure that the heat sink is well-connected, but also that the board design is manufacturable.?

Murky in Albuquerque?

How would you solve this problem?   Tony Koryban has an idea or two, and you can learn his approach by clicking over to:  “Tony Koryban Mailbag Archives

P.S., don’t tell Tony we said this but you can see him, in person, at
Cooling Zone 2010

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