Heat must cross the dielectric
A metal substrate can help spread heat, but the dielectric between copper and metal remains an important part of the thermal path. Review dielectric thickness, thermal conductivity, electrical isolation and the interface to the enclosure or heatsink together.
Define the complete thermal system
Provide device power losses, mounting arrangement, allowable temperatures and environmental conditions. Board construction alone does not determine junction temperature. Contact pressure, interface materials and airflow may dominate the final result.
Manufacturing questions
Confirm isolation requirements around holes and edges, available surface finishes, outline machining and assembly support. Do not transfer assumptions from standard multilayer FR4 designs without a construction review.
Project submission
Attach the layer construction, copper layout, mechanical drawing, mounting details and thermal requirements. The material and process combination must be confirmed for the actual design before a manufacturing commitment.