Best heatsink material? Copper vs. Aluminum vs. Ceramic

 I've been doing some research lately regarding heatsinks for SBCs, like Raspberry Pi. I couldn't find any comprehensive comparisons between copper, aluminum, and ceramic so I decided to do my own testing:

Heatsinks:

• Copper
• 0.8mm shim
• 5mm
• Aluminum
• 5mm
• 6mm
• 6.5mm spiky
• Ceramic
• 6mm

Adhesive:

• 3M double-sided thermal tape (on flayed aluminum): 0.8 W/mK thermal conductivity
• SYY 157 thermal paste: 15.7 W/mK thermal conductivity
• Kritical thermal pad (0.5mm): 20 W/mK thermal conductivity
• LT-100 liquid metal: 128 W/mK thermal conductivity

Fan: Pi-Fan (GF3007BS)

Test SBC: NanoPi NEO3 (Rockchip RK3328 CPU)

Stress Test: CPU crypto mining

Results: link

Best Result: Kritical Thermal Pad + 6mm Aluminum heatsink + Fan

P.S. You can hold the heatsink and thermal pad in place by applying a small amount of thermal glue around the perimeter.

Conclusions:

• Ceramic was okay, but not exceptional
• Liquid metal isn't worth the hassle/risk (thermal paste was within a couple degrees and the thermal pad was actually better)
• Aluminum beating copper was a surprise (size appears to have a bigger effect than material)
• Active is better than passive cooling (in some cases passive cooling was no better than the bare chip)
• If you need a thicker thermal substance than 2.5 mm, go with Thermal Putty CX-H1300 (13.5 W/mK)