Multilayer circuit board

A multilayer circuit board comprising:

• an insulating base including a stack of insulating layers, and a first main surface and a second main surface facing each other in a stacking direction;
• conductor layers between the insulating layers, or on the first main surface, or on the second main surface;
• and
• interlayer connection conductors penetrating at least one of the insulating layers in the stacking direction;
• wherein
• the conductor layers include a first conductor layer, a second conductor layer, a third conductor layer, and a fourth conductor layer, each including Cu foil;
• the interlayer connection conductors include a first interlayer connection conductor sandwiched between the first conductor layer and the second conductor layer in the stacking direction, and a second interlayer connection conductor sandwiched between the third conductor layer and the fourth conductor layer in the stacking direction;
• the first interlayer connection conductor includes a first portion including a single metal including Cu as a main component and a second portion including a single metal or an alloy including Ag as a main component in the stacking direction;
• one end portion of the first portion is bonded to the first conductor layer, and another end portion of the first portion is bonded to one end portion of the second portion;
• an intermediate layer including Cu and Sn is provided at the one end portion of the second portion;
• the second interlayer connection conductor includes a third portion including an alloy including Cu as a main component;
• one end portion of the third portion is bonded to the third conductor layer, and another end portion of the third portion is bonded to the fourth conductor layer;
• and
• an intermediate layer including Cu and Sn is provided at the one end portion and the another end portion of the third portion.