Insulating resin circuit substrate

An insulating resin circuit substrate comprising:

• an insulating resin layer;
• a circuit layer consisting of a plurality of metal pieces disposed to be spaced apart in a circuit pattern shape on one surface of the insulating resin layer;
• and
• a heat radiation layer is formed on a surface of the insulating resin layer on a side opposite to the circuit layer,
• wherein in a case where a surface of the insulating resin layer in a gap between the metal pieces is analyzed by SEM-EDX, an area rate of a metal element constituting the metal pieces is less than 2.5%,
• the insulating resin layer prevents the electrical connection between the circuit layer and the heat radiation layer,
• in a region of the heat radiation layer, a joining rate of the insulating resin layer to the heat radiation layer is 70% or more, where the region is located on a back surface of the gap between the metal pieces of the circuit layer, and
• the heat radiation layer is made of a material having a thermal conductivity higher than a thermal conductivity of the insulating resin layer.