Copper based PCB . 

Copper-based PCBs use copper as a primary base material in place of commonly used FR4. The copper base material is then covered with an insulating layer followed by a circuit layer. Copper core/based PCBs are known to have excellent heat dissipation and can be used for high frequency applications with minimal variation in performance over wide temperature ranges. 

Advantages of Cu Based PCBs:

Their heat conduction is way better than the other substrates like Aluminum and Iron

Suitable for high-frequency operation with high and low temperature variations

The copper core PCBs have higher thermal conductivity, which improves the heat transfer efficiency followed by better heat dissipation performance.