Optimal thermal paste thickness (bond-line thickness) is critical for heat dissipation. The layer should be thin, ideally between 25 µm and 50 µm, which is roughly the thickness of two sheets of standard paper. The paste’s sole purpose is to fill microscopic air pockets between the metal surfaces for better thermal conduction. Source, I spent 6 months in a laboratory experimenting with and producing thermal pastes and insulators. I spent days cutting and cleaning copper squares, applying the experimental pastes, and testing thermal conductivity via the application of Fourier’s Law of heat conduction.

Q = kA(Δ T/Δ X)

Where Q is heat flow, A is the cross-sectional area, and Δ x is the paste’s thickness.

Another source.

That’s way more paste than you need for 50 µm application.

Drops Mic