Wiring board

A wiring board comprising:

• an insulation layer and an electrical conductor layer that are layered, the insulation layer and the electrical conductor layer being in contact with each other, wherein
• the insulation layer is a glass ceramic,
• the electrical conductor layer is a sintered body of a plurality of crystallites containing copper as a main component,
• the plurality of crystallites comprises polygonal crystallites having linear sides, the crystallites being in contact with each other via the linear sides as grain boundaries,
• the electrical conductor layer contains silica particles, and
• the electrical conductor layer has a recessed portion on a surface along the insulation layer;
• wherein:
• the silica particles are present on and within 1 μm of a surface of the electrical conductor layer that faces the insulation layer,
• the silica particles have an average particle diameter of 10 nm or more and 80 nm or less;
• a width of the recessed portion in a direction along the insulation layer is 50% or more of an average thickness of the electrical conductor layer,
• the recessed portion has a radius of curvature of 10 μm or more and 30 μm or less, and
• 70% or more of a number of crystallites among the plurality of crystallites have two or more linear sides.