As a PCB manufacturer. Alcanta PCB company offer Copper board. About the Copper thick. there are some different types. first one: heavy copper pcb. on the FR4 base materials surface. the copper will be made with 2 oz(70um) to 6 oz(210um). Some multilayer boards. the inlayer will make the heavy copper too.
the second types. like a two layer copper pcb. it will be made with the fine copper base. we call it Metal PCB too. you can see the below pictures.we can produce the two layer copper base pcb thick from 0.2mm to 1.6mm. the core will be copper. not FR4 base.
the third type. Some multilayer boards. e.g. 8 Layer FR4 PCB. from L3 to L6 layer. it needs to make 1.2mm thick copper. top and bot side use FR4 base. PCB total fnished thick is 1.57mm. or some Rigid-Flex PCB will make the Copper core.
If you have any questions. please check with our engineer. we produce PCB from 2 layer to 90 layers. high quality, More cheaper price.and fast lead time.our company has made the PCB with IPC Class II and IPC Class III. thanks a lot!