Wiring substrate

A wiring substrate, comprising:

• a first insulation layer;
• a first wiring layer including a pad formed on an upper surface of the first insulation layer;
• a second insulation layer formed on the upper surface of the first insulation layer to cover the first wiring layer;
• a first hole extending through the second insulation layer in a thickness-wise direction of the second insulation layer and exposing a portion of an upper surface of the pad, the first hole including a first wall extending downward from an upper surface of the second insulation layer;
• a second hole formed in the second insulation layer to be continuous with the first hole, the second hole increasing a width of a bottom opening of the first hole thereby exposing a portion of the upper surface of the first insulation layer and entirely exposing a side surface of the pad in a thickness-wise direction of the pad, the second hole including:
• a second wall extending from a lower end of the first wall to an outer side of the first hole;
• a third wall extending from an outer end of the second wall to the upper surface of the first insulation layer;
• and
• a first gap defined between the side surface of the pad and the third wall, the first gap narrowing between the side surface of the pad and the third wall from the upper surface of the pad toward a lower surface of the pad;
• a via wiring filling the first hole and the second hole;
• and
• a second wiring layer formed on the upper surface of the second insulation layer integrally with the via wiring.