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I am designing a PCB board, and it has lots of components on it. It has like 8 MOSFETs, diodes, fuses, current sensors, a STM32 and other components, and with an exception to a few (like mosfets and diodes) the datasheets don't include thermal resistance. To get to the point - I am getting concerned about if my PCB will get too hot, despite having more than appropriate trace specs (3oz copper rated for <20 C rise ). Is there a way to have a general heat sink that just sits on the board? Or am I better off selecting one components and attaching a heat sink to it? or sitting a heat sink on like a copper pad not connected to a component? And if I select a component, how do I decide which one?

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    \$\begingroup\$ Lots of components do not mean too much heat, you should calculate the power dissipations of components individually. \$\endgroup\$
    – emre iris
    Jul 27, 2020 at 16:53
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    \$\begingroup\$ Consider arranging airflow across the board - fan and air duct may make more sense than a heatsink. \$\endgroup\$
    – user16324
    Jul 27, 2020 at 17:14
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    \$\begingroup\$ List one that doesn't have the thermal resistance stated please. \$\endgroup\$
    – Andy aka
    Jul 27, 2020 at 17:31
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    \$\begingroup\$ Capacitors don't dissipate significant power so strike that off the list. The recom regulator has in-built thermal protection. I just did start and end. Convince me you know what you are talking about and pick a component that dissipates significant heat that hasn't got a stated thermal resistance. \$\endgroup\$
    – Andy aka
    Jul 27, 2020 at 19:22
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    \$\begingroup\$ Your RECOM R785 has 70 K/W. Read the datasheet. Compute individual power losses per component. \$\endgroup\$
    – winny
    Jul 27, 2020 at 20:15

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You could do a power plane on the PCB bottom side and mount it on a metal box or a metal plate which could act as a heat sink for the whole board. Then you can use thermal pads with isolation in order to avoid short circuits between different traces or components.

enter image description here

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  • \$\begingroup\$ So I have a lot of THT components on my board. Is this still possible with THT components? \$\endgroup\$
    – Jason Nguyen
    Jul 27, 2020 at 18:46
  • \$\begingroup\$ It is. See for example this picture in my answer where two MOSFET are pressing against the metal box with their drain pin and a thermal and electrically isolating pad \$\endgroup\$
    – SolarTec
    Jul 27, 2020 at 18:53
  • \$\begingroup\$ Ahh ok I see, thanks. Is the thermal and electrically isolating pad the white thing behind the metal pad of the MOSFET? \$\endgroup\$
    – Jason Nguyen
    Jul 27, 2020 at 19:02
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    \$\begingroup\$ That should be a thermally conductive pad, not thermally isolating. You want as good a thermal contact to the heatsink as possible! \$\endgroup\$
    – Hearth
    Jul 27, 2020 at 19:15
  • \$\begingroup\$ Yes, the white thing. It's Electrically isolating. Thermally conductive \$\endgroup\$
    – SolarTec
    Jul 27, 2020 at 21:36

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