Warpage control structure for metal base plate, semiconductor module, and inverter device

A method of forming a warpage control structure for a metal base plate, the method comprising:

• forming the metal base plate;
• forming a dissimilar metal layer on a surface of the metal base plate;
• and
• joining an insulation substrate to a surface of the dissimilar metal layer with a joining material being provided between the insulation substrate and the surface of the dissimilar metal layer, the insulation substrate including a ceramic substrate, an upper metal plate disposed on an upper surface of the ceramic substrate, and a lower metal plate disposed on a lower surface of the ceramic substrate, such that the upper metal plate and the lower metal plate are disposed on both surfaces of the ceramic substrate, the insulation substrate being joined to the joining material, the dissimilar metal layer, and the metal base plate in a high temperature state such that the metal base plate becomes substantially flat at a room temperature state, the high temperature state being between 250-300° C. and the room temperature state being around 25° C., wherein
• α1>α3>α2 is satisfied, where α1 represents a linear expansion coefficient of the metal base plate, α2 represents a linear expansion coefficient of the dissimilar metal layer, and α3 represents a linear expansion coefficient of the upper metal plate and the lower metal plate, and
• the warpage control structure is configured to substantially cancel out warpage in the metal base plate caused by temperature changes.