The effect of heat treatment on the resistivity and structure of electroless Co-P plating films was investigated. The results obtained are as follows. 1) The two types of ammonia alkaline solutions were employed as plating baths. The deposition rate of these baths was affected by bath pH and the phosphorus content in deposited films varied in the range of 1.1-4.3mass%. 2) The resistivity of deposited films was affected by phosphorus content of films and it increased with increasing phosphorus content value. Upon heating the as-plated films, the resistivity was observed to change drastically. These films ware classified into two groups according to thermal behavior of their resistivities. 3) The structural change depending on heat treatment varied considerably with the state of as-plated films. In the films with P>4%, the amorphous structure was transformed into a structure consisting of aggregate mixture of hcp Co and Co2P at 550-650K. While in the films with P<4%, remarkable structural change can not be recognized under 650K and gradual grain growth was observed over 750K. 4) The mechanism responsible for the change of resistivity seems to be described by two different processes. One is the annihilation of grain boundaries which decreases the resistivity, the other process is the formation of Co2P which tends to increase the resistivity.
A new etching system intended for tin oxide films, which had a bath of hydrochloric acid and Cr2+/Cr3+ redox couple formed by electroreduction of chromic ion with the carbon electrodes was investigated. The etching rate was gained as a function of hydrochloric acid and initial chromic ion concentrations and the bath temperature. The etching rate was found to be proportional to hydrochloric acid and initial chromic ion concentrations, and also to increase logarithmically with the bath temperature. It was possible for this system to perform continuous etching by removing of dissolved stannous ion. The finely etched patterns of tin oxide films were obtained in the actual photolithographic etching by this system.
Improvement of mechanical properties of electroless copper deposition for printed circuit boards were investigated. Excellent surface leveling and ductile deposition were obtained from the bath containing 2-2′ bipyridyl and nonion type surfactants. Absorption of hydrogen was also much less than the deposit from additive free bath. The copper deposit from this bath has an elongation of 12% and after soldering no cracking will occure in the deposit. Since Copper Sulfate is used normally to make up and replenishment the plating solution, Sulfate ions accumlate in the bath during deposition. Sulfate ions were shown to adversely affect the ductility. In order to eliminate this problem, electromembrane cell was applied to remove sulfate ions and also an anodic dissolution with copper anode or doseing copper hydroxide instead of copper sulfate showed good results. By these techniques the bath could be used over an extended period while maintaing good properties of copper deposition.
Electroless plating rate measurements for some copper and nickel baths have been made by the coulostatic method. The reciprocal of polarization resistance Rp, obtained by the analysis of the coulostatic decay curve, showed reproducible proportional relationship with the deposition rate for each bath. The proportional constant between them was dependent on the kind of bath but was independent of the electrode material used. The value of double layer capacity Cd was almost constant for the same bath composition, temperature, electrode material and measuring conditions. Based on these electrochemical characteristics of electroless plating, a plating rate monitor which detects time constant (Cd×Rp) of the coulostatic decay was constructed and evaluated with the production electroless copper bath. Results suggest that this monitor is useful for rapid estimation of the deposition rate for production baths.
Thin magnetic films of Co-Ni were prepared by vacuum roll coating technologies with O2 partial pressure using polyester film substrate. The total magnetic flux of these tapes was found to decrease on exposure to high humidity atmosphere. Investigation of sputtered coatings for metal thin film video tape have revealed thinner Si, Ti, Cr, Ni, Zr, Ta, NiO, Cr2O3, SiO2, Si3N4, SiC, and TiC films to be an excellent barrier against high humidity corroding, and the protective effect of these sputtered coatings have a superiority compared with the same thickness films prepared by electron beam heated vapor deposition method.
Selective microplating of thin film Fe-Ni alloys for computer disk heads was studied. An initial anormaly of Fe-Ni alloy plating was found to be emphasized as the plating area becomes very small and to make it difficult to control the chemical composition of 19%Fe-81%Ni and the thickness of a few microns for a plated film on a head device. Such an initial anormaly was interpreted as a relaxation term to the steady state of an anormalous codepositin due to the increase of pH near a cathode. A method of flowing instantaneous high current density prior to a steady plating stage was proposed to hasten the increase of pH near a cathode. By this method, a stable chemical composition and precise control of the thickness of a few microns of plated films were obtained reliably. It was also found that the optimum current density, concerning the decision of the composition of plated films, depends on the total plating area of very small plating region in each plated area on the head device. Poor deposits with dark colored surface were sometimes appeared under certain conditions and SEM images showed that the colored surface has a microscopic roughness. This may be related to the deterioration of the effect of addition reagents.
The electric resistance behavior and the structure of electroless nickel-copper-phosphorus alloy films obtained from various kinds of plating baths containing sodium hypophosphite as a reducing agent were investigated by means of an X-ray diffraction method, a film resistance measurement, and a differential scanning carolimetry. It was found that resistivity of films as-plated became constant value more than 1-2μm thickness, and it became smaller when the contained the larger content of copper. For change of resistivity of films by the heat treatment, the ratio of its decrease became larger when the films contained the larger content of phosphorus and its relation corresponded well to the structural variation of films. For the films deposited from caustic alkaline citrate bath, the returning of films became worse, when content of copper incresed. The heat treatment at 300°C 1hr. in vacuum, however, developed its returning. In case of ammonia alkaline citrate bath, the returning of films were better than that deposited from caustic alkaline citrate bath. In all films asplated, the resulting temperature coefficient of resistance (TCR) were lower with decreasing the grain size of film and TCR were larger by the heat treatment.
The effects of PbO-SiO2-Al2O3 glass passivation on mesa-typed power transistors were studied to improve the reverse characteristics and reliability of the power transistors. The glass was deposited on silicon substrate by electrophoresis in which methanol was used as a suspension and AlCl3 was used as an additive electrolyte, after that, it was fired. Relation between deposition rate of glass and conditions of electrophoresis was investigated. It was found that uniformity of thickness of glass film depended on the content of additive. Relation between growth of glass film and deposition time, deposition voltage during the electrophoresis was discussed. Moreover, dependance of reliability on thickness of glass film was investigated. The dependance of reverse characteristics of the glass passivated silicon p-n junction on the condition of firing, for example firing time and firing temperature were observed. The power transistors on which glass was passivated under the best condition have demonstrated excellent results through bias-temperature-test, proving that they have made rapid progress in reliability.
The effect of heat treatment on the magnetic property of electroless Ni-P deposits was studied with a view to develop a stable non-magnetic film. It was observed that Bs of saturation magnetic flux density, and the structure of Ni-P deposits, plated in citrate baths, were greatly influenced by the three factors of the bath; pH, nickel sulfate and hypophosphite concentrations. Even from an alkaline bath, the same films having a high phosphorus content as from an acidic bath were obtained when the nickel sulfate concentration was decreased. The as-plated Ni-P films whose phosphorus content was less than 8wt% showed always ferromagnetism and a sharp peak corresponding to the Ni (111) plane was observed in their X-ray diffraction patterns. The Bs value continuously increased with a rise in heat treatment temperature. The as-plated Ni-P films containing phosphorus more than 10wt% were always non-magnetic and this property was kept unchanged up to 275-300°C. At the region of phosphorus content between 8 and 10wt%, the film properties were controlled not only by the phosphorus content but also by bath operating factors such as pH, nickel sulfate and hypophosphite concentrations. For example, as-plated films belonging to the above region became non-magnetic or ferromagnetic depending on bath operating conditions even in the case of the same phosphorus content films. The stability of keeping a non-magnetic state of Ni-P films plated at the optimum bath pH 8 was further improved by the addition of a cationic surfactant into the bath.