The behavior of Cu+ ions produced in the course of copper anode dissolution in an acid copper sulfate solution was investigated electrochemically using a rotating Pt disc electrode system. The Cu+ ion concentration of the solution was proven to be related to the natural potentials, Er, of the Pt electrode. The amount of Cu+ ions produced by a phosphorous deoxidized copper anode was found to be much smaller than that from an electrolytic copper anode as noted by monitoring the Er of Pt electrode dipped in the solution. In addition, Cu+ ions accumulating in the solution were easily oxidized by air bubbling, resulting in suppression of copper slime generation. Therefore, an anode slime free-copper plating system was proposed. The system was equipped with double anodes, a copper anode and a dimensionally stable anode, in an anode compartment cell separated from the plating solution by a cation exchange membrane. No copper slime was observed in the anode compartment and the bath composition remained practically constant during a long period of plating operations.
The electrodeposition of Zn-Cr alloys from sulfate solutions was conducted using rectangular pulsed current. Changes in the current efficiency and the Cr content in the deposits with varying values for the average current density showed similar results as seen in direct current plating. Cr in the deposits existed in both its metallic and trivalent states in the pulsed current plating, while no metallic Cr was observed in the deposits in direct current plating. Results thus indicated that the use of pulsed current increased the limiting current of Zn to attain the deposition potential of Cr. The superimposition of direct current on pulsed current allowed a significant increase in the content of metallic Cr in the deposits, suggesting that the superimposition of direct current prevented the reoxidation of Cr in the deposits during the off-time period of pulse plating. Varying the plating conditions resulted in the cathode being polarized to an extremely negative region where mass transport became predominant. At that point, the deposits contained a considerable amount of trivalent Cr, which was the product of hydrolysis resulting from the accelerated decomposition of water.
Flip chip (FC) bonding and chip size packaging (CSP) have progressed along with the development of surface mounting manufacturing technology. Micro bumps must be formed to connect the circuits and electrodes on semiconductor chips. Aluminum alloy has generally been used for circuits or electrodes in semiconductors. Electroplating and electroless plating have been used to form the metal bumps on aluminum electrodes. A zincate method has been adopted as a pretreatment step as part of the electroless plating process. However, aluminum is attacked by the high alkaline zincate bath. Therefore, this research investigated the use of direct nickel plating on aluminum and the formation of nickel bumps without the zincate method. This study involved application of direct nickel plating on the aluminum pads of the semiconductor chips. As a result, deposition behavior on the signal and the ground pads differd and uniform bumps were not formed. This phenomenon is thought to be due to the potential difference in the signal and the ground pads. Uniform bump formation on aluminum pads can be achieved by increasing the load factor and reducing the DO (Dissolved Oxygen) level in the electroless nickel bath. Nickel bumps with a uniform and smooth surface can be formed on the signal and the ground pads by the optimization of the reactivity of electroless plating. Furthermore, uniform gold plating on the nickel bumps has also been achieved.
Quantitative analysis of acid and base groups contained in a resin solution for an electropaint system is important parameters to analyze characteristics of the resin solution. Analysis is generally performed with potentiometric titration after dissolving the resin solution into a tetrahydrofuran (THF) solvent. Researchers have empirically understood that the measurements involved in analysis include a certain amount of analytical errors. This study investigated the influence of water-THF used as a solvent on quantitative analysis for acid and base groups in an electrodepositable resin solution in order to minimize analytical errors. THF is more basic than water and produces no leveling effect on a strong base as a solute. Thus, only a blank test for KOH titration produced a blank value, but the blank test for HCl titration yielded no blank value. Results indicated that the blank values obtained from the blank test of KOH titration depended on relative dielectric constant of the solvent used for the titration. Adjustment of the relative dielectric constant to 20 to 40 by mixing THF with water minimizes the blank value.
The effects of the surrounding humidity on the friction and wear properties of electroless Ni-P-PTFE composite coating on iron substrate against steel ball were evaluated by using a horizontal reciprocating friction and wear test apparatus. The friction and wear properties greatly changed due to the surrounding humidity in spite of being under equal friction and wear testing conditions. Disregarding the variation of surrounding humidity, the friction coefficient lowered with the increase in the PTFE particles into a coating. On the other hand, the wear amount of composite coating increased with the increase in the surrounding humidity.