A clamping apparatus and method for maintaining a workpiece flatness during processing includes a base having a planar surface for receiving a first workpiece. Two sets of opposing clamping mechanisms are mounted to the base and include a clamp head at a distal end of a rod extending from a housing in removable overlapping relation to the first workpiece. Each set of the clamp heads are in opposing spaced relationship to each other defining a second workpiece area, and the clamp heads are configured to mate with a top surface of the first workpiece. A biasing member is coupled to each of the housings and apply a downward vertical force to the housings, rods, and the clamp heads for applying a downward vertical pressure to the first workpiece. The first workpiece is thereby discouraged from thermally expanding in a vertical direction and is thermally expandable horizontally along the planar surface.