Circuit boards and electronic devices

Circuit board, the metal circuit plate, and a metal heat dissipating plate disposed below the metal circuit plate, a metal heat dissipating plate disposed below the heat diffusion plate, the metal circuit plate and the heat diffusion plate is disposed between the upper surface is joined to the lower surface of the metal circuit plate, the lower surface is disposed between the insulating substrate is joined to the upper surface of the heat diffusion plate, a heat diffusion plate and the heat sink, the top surface is the heat diffusion plate of it is joined to the lower surface, a lower surface and an insulating substrate bonded to the upper surface of the heat sink. The particle size of the metal particles contained in the thermal diffusion plate, from each of the upper and lower surfaces of the heat diffusion plate is smaller toward the central portion in the thickness direction of the heat diffusion plate.