Resin board, method of manufacturing resin board, circuit board, and method of manufacturing circuit board

A resin board comprising:

• a first resin layer;
• a columnar electrode buried in the first resin layer, the columnar electrode including a protruding portion that protrudes from a side surface of the columnar electrode and configured to cause an electric field applied to the columnar electrode to shift to inside of the first resin layer, the protruding portion having an exposed surface exposed from the first resin layer and a non-linear lateral surface connecting the exposed surface and the side surface, such that the exposed surface and the lateral surface form an obtuse angle;
• and
• a second resin layer formed on the first resin layer so as to be in close contact with no gaps and including a plurality of wiring layers electrically connected to the columnar electrode through the exposed surface,
• wherein a portion corresponding to a maximum diameter at the lateral surface of the protruding portion is embedded in the first resin layer,
• a diameter of the exposed surface is smaller than the maximum diameter, and
• the exposed surface has a shape which is recessed in a direction different from a direction of the second resin layer at a surface of the first resin layer.