Study On The Nickel Micro-nanocones Array Materials Fabricated By Electrodeposition

The micro-nano array materials, owing to their unique structure, large specific surface area, high chemical activity etc., have shown special characteristic in optics magnetics and electronics. They are widely used in microelectronics, new energy, medical instrument, chemistry, military and many other fields. However, only a few methods were developed to fabricate micro-nano array materials, and most of them are AAO template-based methods or LIGA photolithography, which are complicated and costly in manufacturing process. And the dimension of the structures is limited to the available templates.In this dissertation, a novel method named directional electrodeposition is presented, which is low-cost and easy for application. The technique of directional electrodeposition method to fabricate nickel nanocones array is studied in details. The microstructure as well as the deposition mechanism of the nanocone is investigated by extensive structural characterization and electrochemical techniques. The basic properties of this material are also characterized, and its potential application in microelectronic packaging is raised as well. The main contents and conclusions are shown as follows:First, the morphologies of the deposits obtained from two metal main salts and four additives were compared, and the additive containing ammonium was found to be an effective crystallization agent in nickel chloride solution to fabricate nickel nanocone array by directional electrodeposition method. And through the study on the influence of the crystallization agent concentration, the prescription of the bath can be obtained. The deposits obtained in many different depositing conditions were compared. The solution temperature, current density as well as the deposition time was found to be the main factors influenced on the morphology of nanocones array. Thus the cones size can be varied from 50 to 1500 nm in height by controlling the deposition conditions.The influences of crystallization agent and solution temperature to the nickel deposition were discussed by studying the plating bath and basic electrochemical behaviors of the nickel nanocones array deposition. The calculated apparent active energy of the reaction confirmed that the reduction process was not controlled by dispersion. The initial stage of nickel nanocones electrocrystallization follows the mechanism of three dimension instantaneous nucleation growth. The electrochemical impedance spectroscopy indicates that nickel nanocones electrodeposition occurs in two steps; the low frequency capacitive loop may be due to the inhibition of nickel electrodeposition by adsorbed crystallization agent. The mechanism and equivalent circuit of nickel electrodeposition were proposed on the basis of the analysis of electrochemical impedance spectroscopy. Meanwhile, the kinetics law of nickel electrodeposition was investigated by means of steady-state polarization to confirm the proposed reaction mechanism.The microstructures of the nanocones were characterized by field-emitting scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and Transmission Electron Microscope (TEM), etc. The results indicated that the nickel deposits'preferred orientation is changed from (111) to (011) texture. A single nanocone is pentagonal symmetric, which is supposed to be a multiple twinning crystallite with (110) orientation axis, (100) sides and twinning at each corner of the (111) planes. The growth mechanism of the nanocones by this method may be explained by the single screw dislocation growth theory. According to the theory, it can be concluded that the aspect ratio of the nanocones is proportional to the square root of the current density. And the propagation of the step edge might be blocked by adsorbed crystallization agent to promote up growth of the nanocones.The characteristics of nickel nanocones array material were also investigated in this dissertation. The results show that the Ni nanocones array materials have 3 times larger specific surface area than the common plain surface. UV-Vis reflection spectrum shows that the reflection rate of nanocones array structure is below 10% in the entire UV-visible range, indicating a good absorption performance; Ni nanocones array material is demonstrated to have the easy axis of magnetization paralleled to the substrate plane. The coercivity of this material is much higher than that of bulk nickel metal. The nickel nanocones array shows very good field emission properties. The nickel film with micro-nano cones array hierarchical structure fabricated by two-step electro-deposition, shows super-hydrophobic characteristic without any chemical modification.Finally, the nanocones array was attempted to apply to electronic packaging. The nanocones array structure was introduced into the Pd pre-plated leadframe (PPF). The adhesion between the epoxy resin molding compound (EMC) and the nanocone-arrayed PPF was three times higher than that of the conventional PPF, and PPFs with taller and steeper nanocones had greater bonding strength with the resin. The increased surface area and the physical keying effect play important roles in this adhesion strengthening between the Pd-PPF and the resin. This approach offers a promising alternative for the synthesis of novel Pd PPF and contributes to solving the problem of weak adhesion between Pd PPFs and EMC. The Au wire bonding strength and the solderability of the nanocones array Pd PPF were also tested. The results showed that both the Au wire bonding strength and the solderability of the nanocones Pd PPF were comparable with the conventional Pd PPF and could reach the industry requirement well. These results indicate that the nanocones arrayed Pd PPF can meet the high reliability requirements, especially for the automobile industry.