Circuit board and electronic device including same

A circuit board comprising:

• a ceramic sintered body having a plate shape with first and second main surfaces, and comprising a through hole penetrating from the first main surface to the second main surface;
• a through conductor in the through hole, comprising a metal and having a first end at the first main surface and a second end at the second main surface;
• and
• a metal wiring layer covering the first end and electrically connected to the through conductor,
• wherein the through conductor comprises:
• a first portion that has a hollow cylinder shape is in contact with an inner wall of the through hole, and extends from the first end to the second end;
• and
• a second portion that has a columnar shape, is located inside the first portion, and is in contact with an inner wall of the hollow cylinder;
• wherein the second portion has a second average crystal grain size of the metal that exceeds a first average crystal grain size of the metal of the first portion;
• and
• wherein the through conductor contains glass, and the second portion has a glass content higher than a glass content in the first portion.