TWI818122B

A copper alloy plate material according to the present invention has an alloy composition comprising 0.3 to 2.5% by mass of Co, 0.1 to 0.7% by mass of Si and a remainder made up by Cu and unavoidable impurities. When a longitudinal section of the copper alloy plate material which is parallel to the rolling direction of the copper alloy plate material is subjected to a crystal orientation analysis by an EBSD method, the ratio of the area of a measurement spot region having a reliability index (CI value) of 0.2 or less to the total area of all of measurement spot regions is 40% or less. When the longitudinal section is divided into a pair of surface layer parts respectively including both surfaces of the plate material and a center part located between the pair of surface layer parts and the average value of the reliability indices (CI values) of the pair of surface layer parts is defined as CIS and the average value of the reliability indices (CI values) of the center part is defined as CIC, the ratio of CIS t