Thermal and mechanical load
Engine-bay electronics see repeated thermal cycles and vibration. Via reliability depends on plating thickness and laminate expansion, so the stackup and copper weights are chosen together.
Documentation
IATF 16949 requires control plans, traceability and change management. A supplier that cannot show lot records cannot support an automotive program, whatever the price.
What to send
Operating temperature range, thermal cycling requirement, connector and housing constraints, and the documentation level the customer's quality system expects.
