Method and apparatus for reducing the shrinkage of an optical disc's clamp area, and the resulting optical disc

摘要

An improved optical disc is provided that comprises a substantially transparent substrate, one surface of which carries optical data structures comprising pits and lands radially outward of a clamp area of the disc. In the clamp area a protrusion structure (60) is provided above the first surface to create a clamp thickness greater than the thickness of the rest of the disc. In accordance with the principles of the present invention, only a portion of the clamp area is covered by the protrusions, which emulate a disc having a clamp area of greater thickness. In order to reduce warping caused by shrinkage of material added to the clamp area, the amount of material used to form the protrusions is less than 5% of the amount of material used to form the rest of the clamp area.