Thanks, yes , it is out there , as you kindly say..
https://jlcpcb.com/impedance...we are now seeking a 1mm thick board , 4 layers, each 2oz, and no core, just pre-preg separating the copper layers.
But we cant find anybody who does this?
We like it that pre-preg is soft and rubbery and compressable, and we want that, not the tough rigid core.