A platen having different grounding structures is disclosed. Different grounding structures, such as pins, flat-end posts and mushroom-shaped grounding structures, may be disposed on the surface of a platen. Each type of grounding structure may be advantageously used with a particular type of workpiece. In one embodiment, all of the different grounding structures are mechanically biased upward, such as by springs, from the surface of the platen such that all may contact the back surface of a workpiece disposed on the platen. In another embodiment, one or more actuators are used to lift and lower subsets of the grounding structures such that only a subset of the grounding structures contacts the back surface of the workpiece. These subsets may be all a single type of grounding structure, or may be associated with a particular type of workpiece.