Copper base substrate comprising an insulating layer having a specific relationship between thickness and elastic modulus

A copper base substrate,

• wherein a copper substrate, an insulating layer, and a circuit layer are laminated in an order in the copper base substrate,
• a ratio of a thickness (unit:
• μm) to an elastic modulus (unit:
• GPa) at 100° C. is 50 or more in the insulating layer,
• the circuit layer contains copper and has an elastic modulus at 100° C. of 100 GPa or less,
• the elastic modulus at 100° C. of the circuit layer is measured by dynamic viscoelasticity measurement,
• the circuit layer is thinner than the copper substrate, and
• the elastic modulus of the circuit layer is lower than the elastic modulus of the copper substrate.