HMC8205 - How to keep the conductivity between PCB and heatsink strongly?

Hello,

The flange is the only GND for this device. So, the route of GND is as bellow and the interface between them is very important.

flange -> heatsink -> PCB

How to keep the conductivity between PCB and heatsink strongly?

EVB seems that there are no studs or screws to fix PCB and heatsink.

I think conductive grease has a weak fixing force and poor electrical characteristics.

Thanks.

  • 0
    •  Analog Employees 
    on Oct 28, 2021 12:29 PM

    Hi RZM,

                      On the HMC8205 EVB, There is a milled pocked to accept the flange of the HMC8205. The HMC8205 rests on an Indium foil shim and the flange is screwed to the heat sink. The screws are fastened using a torque wrench to prevent over tightening and cracking the ceramic. 

    During bench test we use thermal grease on the backside of the EVB heat sink/plate and clamp the EVB to a thermally controlled plate.

    The mechanical plate used with the EVB has 4 thru holes and two threaded holes that can be used to mount an external heat sink. See attached.

    Regards,

    Jim B

  • Hi Jim,

    Thank you for reply. I checked HMC1114 datasheet.

    EVB is similer to HMC8205, but HMC1114 is CSP package and there is no GND flange (see below).

    So, there is no cut out on PCB and heatsink needs not to have the role of connecting GND.

    On the other hand, in HMC8205, heat sink is the only path for GND, so I am concerned about its connectivity.

    Looking at the EVB picture, there is a silver substance attached between the PCB and the metal plate. Is it entirely soldered?

  • 0
    •  Analog Employees 
    on Oct 28, 2021 1:36 PM in reply to RZM

    Hi Rzm,

                         I meant the HMC8205 data sheet. I edited my post above to reflect the HMC8205.

    Regards,

    Jim B

  • +1
    •  Analog Employees 
    on Oct 28, 2021 1:46 PM in reply to Jim

    Hi RZm,

                      The PCB is either soldered to the plate or attached with conductive epoxy. The drawing specifies epoxy. The data sheet for the material is below. 

    https://www.bondingsource.com/techdata/5025E.pdf

    Regards,

    Jim B