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I need some help designing proper thermal management for my board. It's a mixed analog-digital circuit, the analog part is noise sensitive. I have +/- analog supply, and a + digital supply. Several of my components do not even have exposed pads. Some do have, but I have to connect them to the negative supply, while some must be connected to GND. The maximum specified total dissipated heat will be on the order of a few W.

My question are:

  • Apart from the exposed pads that I should connect to the negative analog supply, it would be enough to have 4 layers. Should I use 6 layers nonetheless to have a separate negative power plane to extract heat? If yes, which layers I should use as power planes?

  • What is a good practice to remove heat from the board? I mean, heat will be dissipated into 2 or 3 different layers (top, GND, V-). Should I just create a copper fill at the side of the board where I can attach a heat sink? Should I connect it to GND, or just leave it unconnected?

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  • \$\begingroup\$ Who can say without precise numbers, board surface areas, other heat removal processes (heat-sinks, fans etc.). \$\endgroup\$
    – Andy aka
    Commented Jan 12, 2023 at 10:39

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Without knowing much details (device footprints, dissipated power) is hard to give conclusive help, but here are some hints to your questions:

  1. I don't expect that more layers would help much. I would rather go to thicker copper layers, and place them on the outside layers, they have better heat transfer as inner layers.

  2. I would add heatsinks (available for most SMD and THD footprints) and thermal vias wherever possible.

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  • \$\begingroup\$ Thank you for the help! I'll go for 4 layers. Looks to me that by heatsink you mean exposed pads? Those I have added wherever possible. I'm thinking about adding like a 10 mm stripe of copper, and design the mounting of the board as such that it will be in contact with the bulk metal casing. Should I leave this copper floating, or maybe connect to GND? \$\endgroup\$ Commented Jan 17, 2023 at 10:49
  • \$\begingroup\$ No, with heatsink I meant something like this: digikey.com/en/product-highlight/a/aavid-thermalloy/… \$\endgroup\$
    – Ken Grimes
    Commented Jan 18, 2023 at 9:49
  • \$\begingroup\$ Regarding floating: It's hard to say without an EMC analysis. My advice would be to design the PCB so that you leave pads to be able to externally connect that copper with ground, with a thin copper plate for instance, and simply to make the test if grounding that copper makes any difference \$\endgroup\$
    – Ken Grimes
    Commented Jan 18, 2023 at 9:51

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