| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 94 === Ink-jet printing, as a derivative of direct-write technology, offers the additional advantages of low cost, high material efficiency, elimination of photolithography, low temperature deposition, friendly environment and non-contact processing. Therefore, it has great potentials for applications on electronics fabrication processes, especially on plane and flexible substrate in recent years. In this study, ink-jet printing is combined with electroless plating which has been fully developed and direct writes cooper and silver lines at low temperature.
First, the mixed-potential theory is applied to investigate the effects of reagents concentrations in both electroless copper and silver plating systems. In the electroless copper plating system, the change in copper concentrations has more effects on the deposition current density than formaldehyde. As compared with the silver system, the mixed potential is more negative, which means the occurrence of copper deposition is not as easy as silver. The reduction rate of silver ion is very fast and silver deposits almost immediately when the silver ion solution meets the reduction agent solution, hence it is suitable for applying to the ink-jet printing system. The thickness of ink-jet silver lines in this study is about 100 nm and the resistivity is 4.4 μΩ-cm. In the electroless copper plating system, copper can deposit very fast on a catalyzed surface by adding 1.0M KOH in the solution to adjust it to a high-pH condition. The reaction completes within about 12 seconds by the prediction of the mathematical model established in this study. The thickness of ink-jet copper lines is about 25 nm and the resistivity is 11 μΩ-cm. Hydrogen is a by-product in the reduction reaction of copper and it comes in a large amount when the copper reduction rate increases. The large amount of hydrogen would cause the discontinuity of surface of copper lines and hence affect the conductivity. Furthermore, the printing head would easily get corrosion in a strong-base environment and hence end its life.
Metallization by ink-jet printing based on electroless plating, different from traditional electroless plating bath which calls for the stability of plating bath, needs high reduction rate of metals. The thickness of metal deposited has no relations with reaction time and temperature, but it can be controlled by adjusting the reagents concentration in ink solutions or by jetting multi-layers of metal to form a thicker conductive lines.
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