Application of Electroless Ni(P) Metallization to LCD Backlight Unit with Carbon Nanotube Field Emitters

Backlight unit (BLU) is one of essential components constituting liquid crystal display (LCD). It can be fabricated with several different methods. Cold cathode fluorescent lamp (CCFL) can be made with a low cost process and has high quality of color reproducibility. But it cannot provide a high quality of brightness & contrast and can raise environmental issue since Hg is used as a law material. White light-emitting diode (WLED) has long lifetime and dynamic control feature, but it has complicated structure and needs high fabrication cost. Meanwhile, carbon nanotube based BLU (CNT-BLU) enables local dimming and impulse & scan driving, and can accomplish best quality of moving pictures by maximizing brightness & contrast functions. However, high fabrication cost is a large barrier for commercialization. In this study, we applied low-cost electroless deposition process of the metallization comprising CNT-BLU substrate. Current fabrication processes of CNT-BLU go through several times of photo patterning and firing of CNT paste, which results in complicated and high-cost processes. Metallization of backlight unit can be made either with Cr (Mo) patterning using conventional photo process or with stencil printing of Ag paste. The former uses vacuum processes using expensive semiconductor equipments such as sputter and evaporator, and the latter uses expensive law material like Ag. BLU substrates are formed by firing and activating the CNT pastes which was printed on the metallizations. Fabrication of BLU substrate can be simplified with electroless deposition method and the cost can also be much lowered. In the present study, feasibility of electroless metallization on the CNT-BLU substrate was tested. Glass substrate was pretreated with base solution and then etched with buffered oxide etch (BOE) solution, followed by seeding process by alternating dipping the substrate in Sn and Pd solution in turn. Electroless Ni(P) deposition was conducted on the sub- strate using a commercial Ni(P) bath with varying P content (4-9 wt%). Adhesion test was conducted with as-plated and fired specimens. The Ni(P) film with low P content showed better adhesion performance than those with high P content. Electrical conductivity was also high in the low P containing specimens. Sheet resistances of them, measured by four point probe, were several ohm/sq and it decreased one order of magnitude lower after firing at 460degC. Decrease of resistance results from phase transformation of metastable Ni(P) film into stable Ni & Ni₃P phase. Surface roughness of the substrate was ~90 nm after BOE etching and ~200 nm after Ni(P) deposition with 2 mum thickness.