Individual target segments (A-F), are mounted on a mounting plate by means of locating studs inserted into mounting holes of elongate or circular cross sections in correspondence with the change in length caused by the thermal expansion of the target segments. The segments are retained by screws received in tapped bones in the studs, which are welded to the target backplates. The individual segments (A-F) each consist of a target backplate and a target bonded to the backplate. The perimeter of each backplate over laps the perimeter of each target segment, this overlap amounting to 0.05-0.2 mm when molybdenum or titanium is used for the target backplate and an indium-tin alloy is used for the sputter target.