Improvement of dimensional accuracy of blu-ray disc cover layer

Abstract

In order to obtain uniform thickness of a blu-ray disc cover layer, a CFD analysis and an experimental comparison of the cover layer thickness distribution during the spin-coating process were conducted. The blu-ray disc, a next generation optical disc format having 25GB capacity over, consists of a thermoplastic polymer substrate layer which has a thickness of 1.1mm, a sputtered reflective metal layer and UV polymer cover layer which has a thickness of 100μm. Especially, the cover layer, which primarily governs the optical quality of the disc, is made by a precise spin coating process. However, it is still hard to get a satisfactory coating uniformity, typically, the thickness variation of the cover layer should be maintained under ±3μm, because of the unavoidable bump formed around the rim of the disc. In order to improve the dimensional accuracy of the cover layer, first, through the CFD analyses of spin coating process, the optimal spin coating conditions were obtained; and second, the edge of the disc substrate was modified into various shapes, such as chamfer, round, step, the height of the bump can be kept under the desired accuracy.