Circuit board and semiconductor module

A circuit board comprising:

• a ceramic substrate with a thickness of 0.5 mm or less including a first surface and a second surface and;
• a first metal part including a first metal plate joined to the first surface and a protrusion projecting from the first metal plate;
• and
• a second metal part including a second metal plate joined to the second surface, wherein
• the thickness of at least one plate selected from the group consisting of the first and second metal plates is 0.6 mm or more,
• a ratio of the total volume of the second metal plate to the total volume of the first metal plate is larger than 1.0,
• if the ceramic substrate is equally divided into first to third sections along a longer side direction thereof,
• the first metal part has a first region overlapping the first section, a second region overlapping the second section, and a third region overlapping the third section,
• the second metal part has a fourth region overlapping the first section, a fifth region overlapping the second section, and a sixth region overlapping the third section, and
• a volume V1 of the first region, a volume V2 of the second region, a volume V3 of the third region, a volume V4 of the fourth region, a volume V5 of the fifth region, and a volume V6 of the sixth region are numbers satisfying
• formula V4/V1+V6/V3≤2(V5/V2),
• 0.5≤V4/V1≤2,
• 0.5≤V5/V2≤2, and
• 0.5≤V6/V3≤2.