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I know that, most of the time, heat transfer and conductance go hand in hand. But is there some material that is an electric insulator while being good (or at least not that bad) at heat transfer?

I don't need extreme solutions such as in this question:

Is there a material that conducts heat well and has a very high melting point, but is also an insulator?

Put simply, I have a laptop from which top cover(aluminium plate) could be removed for a long period of time (and even forever) while the motherboard is still operating. The motherboard should be protected from dust and operator curiosity. So I need to close the laptop with a thin layer of a material that should :

  • protect the user from shock hazards (from typical currents and intensities you find in laptop motherboard)
  • be thin.
  • help dissipate moderate heat (rest of the enclosure will be in aluminum and there will be a fan so temp should be well below 100°C)
  • be puncture resistant if someone put his finger and press it against underlying PCB.

Surface will be around 30 x 15 cm.

I welcome any other suggestion.

EDIT:

When I think about it, it looks like I exactly described a thermal pad. Would a thermal pad provide an effective protection against shocks? I guess if this is designed to not short circuit the board then a fortiori it will protect humans.

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    \$\begingroup\$ A diamond is the best heat conductor, but an electrically it is insulator. Probably not very suitable for your application though... \$\endgroup\$
    – Eugene Sh.
    Aug 8 at 21:17
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    \$\begingroup\$ What is wrong with the existing laptop enclosures? What are you trying to solve? \$\endgroup\$
    – Eugene Sh.
    Aug 8 at 21:25
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    \$\begingroup\$ I think you need to quantify your electrical and heat conductivity requirements to get a meaningful answer. You might get better answers on the physics or engineering stacks. \$\endgroup\$
    – Theodore
    Aug 8 at 21:40
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    \$\begingroup\$ If we are talking about your typical laptop, the operating voltages are very low to be a hazard for the operator, assuming it is not connected to mains, or the power supply is not critically damaged to pass the mains voltage to the laptop. The only danger is to the equipment itself. \$\endgroup\$
    – Eugene Sh.
    Aug 8 at 21:43
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    \$\begingroup\$ Do you really "need the mainboard to be still safe for operator", or do you need it to be safe from the operator? There are no voltages high enough to be a shock hazard in any even remotely normal laptop, but exposing the innards would make it far more likely that someone careless would drop something in and break it. \$\endgroup\$
    – brhans
    Aug 10 at 0:35

1 Answer 1

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You could go with ceramic heat spreaders or maybe pyrolytic graphite sheets if the electrical conductivity of 10000 S/cm is acceptable. If the power supply is <60VDC and its output is internally isolated from mains, the system can be made SELV but depending on the setup, you might want something a little more robust and I would not recommend using any of the materials as a structural component. There are also some more engineered heat spreader sheets that could fit the bill and many other types of thermal pads/sheets that can effectively transfer heat from your motherboard to the case while also preventing e.g. case flexure from shorting out the circuit.

Edited to incorporate some of your comments.

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  • \$\begingroup\$ As thinness matters, pyrolytic graphite sheets look like a very good choice. \$\endgroup\$
    – v1nce
    Aug 8 at 21:52
  • \$\begingroup\$ There should be no (or little) flexure of the pcb or enclosure. \$\endgroup\$
    – v1nce
    Aug 8 at 21:57
  • \$\begingroup\$ The gap between the board and the case is an important variable when choosing a thermal interface pad, as is the difference in height between components. Some pads are optimized for narrow gaps between two plane surfaces and require very high mounting pressures for optimal performance; these are almost like sheets of thermal grease. Some are more sponge-like and are designed to accommodate variance in gap width (gap filler pads). If you have components putting out lots of heat - high performance processors, regulators, etc - the time to perform a detailed thermal analysis is now. \$\endgroup\$
    – vir
    Aug 8 at 22:05
  • \$\begingroup\$ When I see thermal conductivity of PGS are well above aluminium, i think I overstated my needs in thermal conductivity. I need the sheet to "not block that much" heat transfer so that it could transfer it to the aluminium plate that could be above the thin layer. But this would be more of a bonus to help cooling that already takes place in the rest of enclosure. So if price is not a problem (will check) PGS look really nice. Otherwise I'll go for other heat-conductive sheets. \$\endgroup\$
    – v1nce
    Aug 8 at 22:08
  • \$\begingroup\$ PGS is more for spreading heat within the plane of the sheet rather than from one face to another. From what I gather of your application, I do not think that PGS is the optimal material. \$\endgroup\$
    – vir
    Aug 8 at 22:09

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