Electroformed nickel stamper for light guide panel in LCD back light unit

Abstract

Nickel stampers used for injection moulding of 15 in. (307 mm × 232 mm) micro-prism patterned PMMA light guide panel were successfully duplicated from an expensive master by nickel electroforming. The thickness of nickel stamper was 507.5 ± 22.5 μm. The thickness variation of 4.4% was achieved by precise positioning of the anodes. Internal stress was found to be critical in this kind of flat geometry. Uncontrolled and excessive internal stress caused buckling and peeling of stamper, sometimes resulting in ruining the expensive master due to electrolyte leakage through the gap. Therefore internal stress had to be carefully controlled within 0–2000 psi tensile and 0 compressive stress. This could be achieved by frequent purification of electrolyte by dummying, activated carbon treatment and anode bag cleaning. Chloride-free nickel sulfamate bath was used in this experiment. The bath contains 81 g/l Ni ++, 36 g/l boric acid and 5 ml/l wetting agent. Bath pH and temperature were 4.5 and 50 °C, respectively. The current density was 15–20 mA/cm 2. Ultimate tensile strength, yield strength, % elongation and hardness of the nickel stamper were 75.1 ksi, 46.8 ksi, 11.7% and 200 DPH (200 g), respectively.