Power module substrate, power module substrate with heat sink, power module, and method of manufacturing power module substrate

A method of manufacturing a power module substrate which is provided with an insulating substrate, a circuit layer formed on one surface of the insulating substrate, and a metal layer formed on the other surface of the insulating substrate, in which the circuit layer is formed by bonding a first copper plate onto the one surface of the insulating substrate, the metal layer is formed by bonding an aluminum plate onto the other surface of the insulating substrate, and prior to bonding, the first copper plate has a composition containing at least either a total of 1 to 100 mol ppm of one or more kinds among an alkaline-earth element, a transition metal element, and a rare-earth element, or 100 to 1000 mol ppm of boron, the remainder being copper and unavoidable impurities, the method comprising:

• a circuit layer forming process of forming the circuit layer by bonding the first copper plate onto the one surface of the insulating substrate;
• and
• a first metal layer forming process of forming the metal layer by bonding the aluminum plate onto the other surface of the insulating substrate,
• wherein in the first metal layer forming process, any one or more kinds of additive elements among Si, Cu, Ag, Zn, Mg, Ge, Ca, Ga, and Li are disposed at a bonding interface of the aluminum plate, and then the aluminum plate is bonded.