Pure copper plate

A pure copper sheet having a composition comprising:

• 99.96 mass % or more of Cu;
• 0.01 mass ppm or more and 3.00 mass ppm or less of P;
• 2.0 mass ppm or more and 20.0 mass ppm or less of S;
• 10.0 mass ppm or less of a total content of Pb, Se, and Te;
• 3.0 mass ppm or more of a total content of Ag and Fe;
• and
• inevitable impurities as a balance, wherein
• an average crystal grain size of crystal grains on a rolled surface is 10 μm or more, an aspect ratio of the crystal grain on the rolled surface is set to 2.0 or less, and
• a length percentage of a small tilt grain boundary and a subgrain boundary with respect to all grain boundaries is set to 80% or less in terms of partition fraction when a measurement area of 1000 μm2 or more is measured by an EBSD method at measurement intervals of 0.5 μm steps and analyzed except for a measurement point where a CI value analyzed with data analysis software OIM is 0.1 or less, in a case where a boundary between measurement points where an orientation angle between adjacent measurements exceeds 15° is regarded as a large tilt grain boundary, and a boundary between measurement points where the orientation angle is 2° or more and 15° or less is regarded as the small tilt grain boundary and the subgrain boundary, and
• a thickness of the pure copper sheet is in a range of 0.5 mm or more and 5 mm or less.