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This study is aimed at clarifying the mechanism of wear process for Ag plating through a one-way sliding wear test. The samples of different hardness Ag plating on copper alloys were prepared as coupon and embossment specimens, which simulated terminal contacts. During the sliding test, the contact resistance and the friction coefficient are measured. The surface and cross-section morphologies, roughness, tribo-film formation, and wear volume of the Ag films after wear tests were investigated and the wear mechanism was discussed. As results, the hard Ag plating film (120 Hv) exhibited higher contact resistance comparing to the soft Ag plating film (80 Hv). The soft Ag film delivered a larger wear scar on embossment and wider wear trace on coupon specimens compared to the hard one. The overall wear volume of hard Ag film was less than that of soft Ag film, which can be attributed to the fine crystalline structure of hard Ag. Moreover, the observation of tribofilms formed on the Ag films after wear tests suggested that a mixed-type of adhesive and abrasive wears occurred for both of soft and hard Ag films.

The electrodeposition behavior of Sn–Cu alloys in a sulfate solution containing three additives, cresol sulfonic acid, benzal acetone, and nonionic alkyl polyethylene glycol ether surfactant, was investigated potentiostatically between +0.3 and � 0:7 V vs. NHE at 298 K. The contact resistance of the alloys deposited on a Cu connector was evaluated. Cu in the alloys behaved as a more noble metal than did Sn, thus showing the typical feature of regular-type codeposition. In solutions containing additives, the difference in deposition potential between Cu and Sn decreased because Cu deposition was significantly suppressed by the additives. The alloys deposited in solutions containing additives exhibited smooth surfaces and were composed of Cu, Sn, Cu6Sn5, and Cu3Sn phases in accordance with the equilibrium phase diagram of a binary Cu–Sn system. The contact resistance of the alloys increased by heating at 433 K, thus indicating that connecting reliability did not improve by plating with the stable metallic compound Cu6Sn5. The connecting reliability of a connector after abrasion was higher in deposited alloy films than in Sn reflow plating. [doi:10.2320/matertrans.M2011022]

Electrodeposition behavior of Sn–Ag alloys was investigated at current density 1–1000 A·m−2 in both sulfate and pyrophosphate-iodide solutions at 298 K, and the contact resistance of Sn–Ag alloys deposited on a Cu connector was evaluated. In both solutions, Ag behaved as a more noble metal than Sn, showing regular codeposition. The difference in deposition potential between Ag and Sn was 0.4 V in the pyrophosphate-iodide solution and 0.2 V in a sulfate solution containing thiourea as a complexing agent for Ag+ ions. The deposits obtained from a pyrophosphate-iodide solution consisted of blocks of a few microns in size, while those from a sulfate solution exhibited grains smaller than 1 μm. The deposits containing Ag less than 45 mass% were composed of an Ag3Sn intermetallic compound and Sn. This is in accordance with the equilibrium phase diagram of the binary Ag–Sn system. The contact resistance of deposited Sn–Ag alloys, after heating at 433 K for 120 h, was slightly smaller at Ag content below 45 mass% than that of reflow Sn plating. The connection reliability of connectors after abrasion was better in deposited films of Sn–Ag alloys than in those with reflow Sn plating.

Electrical contacts are an important part of electrical circuits and many reliability problems are related to electrical contact failure. It is important to investigate the relationship between load and contact resistance which is an important factor of contact reliability. In this study, the effect of plated material and plated thickness on contact resistance was examined. The samples were constructed of a copper alloy with tin or silver plating. Contact configuration was hemispherical-flat contact. The contact resistance was measured by using a four-probe method with a load up to 40 N. The relation between indentation contact area (i.e. apparent contact area) and contact resistance was determined. As experimental results, the contact resistance depends on the indentation of the contact area. In the same contact area, tin-plated samples have higher resistance than those that are silver-plated due to their own resistivity. The constriction resistance of a plated layer, which depends on contact area, plated material and plated thickness, is analyzed by a theoretical solution, which is shown by R=Φρ/2a, using a surface resistance coefficient Φ, The theoretical results show almost good agreement with the experimental results. Thus, the indentation contact area (i.e. apparent contact area) is almost the same as the real contact area in this study.

Constriction resistance is calculated by numerical analysis using Laplace's equations for electric potential of steady state in many cases of contact spot dispersion-status. The results show that contact resistance does not increase beyond 1.5 times even if the total real contact area is about 15% of the apparent contact area. When real contact area is at least about 60% of the apparent contact area, the contact resistance is approximately the same as the constriction resistance acquired from the apparent contact area. When the real contact area is about 50% of the apparent contact area, the contact resistance is approximately constant without regard to the contact shape and contact-point dispersion layout. Therefore, it is proved that contact resistance can be practically calculated using apparent contact area instead of real contact area when there are many contact points caused by metal to metal contact.

Electrodeposition behavior of Sn-Ag alloys was investigated at 1 to 1000 A/m2 in both sulfate and pyrophosphate-iodide baths of 298 K, and the contact resistance of Sn-Ag alloys deposited on Cu connector was evaluated. In both baths, Ag behaved as more noble metal than Sn, showing the typical feature of regular type codeposition. The difference of deposition potential between Ag and Sn was 0.4 V in pyrophosphate-iodide bath, while it was 0.2 V in sulfate bath containing thiourea as complexing agent for Ag+ ions. The deposits obtained from pyrophosphate-iodide bath consisted of blocks of a few micron in size, while those from sulfate bath showed grains smaller than 1 μm. The deposits containing Ag less than 45 mass% were composed of Ag3Sn metallic compound and Sn in accordance with the equilibrium phase diagram of binary Ag-Sn system. The contact resistance of deposited Sn-Ag alloys after heating at 433 K for 120 hours was somewhat smaller at Ag contents less than 45 mass% than that of reflow Sn plating. The connecting reliability of connector after abrasion was better in deposited films of Sn-Ag alloys than in reflow Sn plating.

Electrical contacts are the most important parts of electrical circuits, and many reliability problems of the circuits are related to contact failure. The contact resistance is one of the important factors for assessing connector reliability, and thus the prediction of contact resistance is essential to designing electrical terminals. In this study, embossments, each I mm to 3 mm in radius, were brought into contact with flat planes to simulate the point of contact on a terminal, and the contact resistance was measured using a four-probe method under a load up to 40 N. Copper alloy samples, each plated with tin or silver and having an embossment of 1 mm to 3 mm in radius, were used and the visually clear indentations resulting from the embossment to plane contact were measured to determine their areas. Since the contact resistance is dependent on the contact area, an FEM analysis must be carried out to determine the contact areas correctly. In this paper, an elasto-plastic FEM analysis was performed taking the plating layers into account, and a method was established to make precise determination of the contact areas for different shapes of contacts and loads. The resultant contact areas were used to calculate the contact resistance, which showed a good agreement with experimental results. It was established that the load-resistance curves can be predicted on the basis of the shapes of the contacts as well as plating.

Due to the recent increase in electronic devices mounted on automobiles, a large number of connectors, especially low-cost tin plated connectors are being used. As a result, their contact reliability has become problematic. Furthermore, for the connectors which are subjected to fretting wear caused by heat cycle and vibrations, the contact resistance increases because of wear of tin and deposition of oxides, which generates problems of poor contact. This study is intended to analyze the change in contact resistance of tin plated connectors from the start of fretting wear to the end of their lifetime from the viewpoint of practical reliability, and to observe the trace and the characteristics of fretting wear microscopically. This study found that wear and oxidation of tin plated connectors start immediately with fretting wear, and thus accumulation of abrasion powder on fretting areas causes connectors to reach to the end of their useful lifetime quickly. Especially, it was demonstrated that amplitude of fretting has a considerable influence on a connector's lifetime. It is made clear that air-tightness, so-called “gas-tight” of tin in a fretting area influences fretting wear considerably.

Tin plating is commonly applied for automotive connectors. To clarify the mechanism of fretting corrosion of tin plating, friction coefficient behavior of tin plating is needed to investigate in detail. In this study, the factors of the friction coefficient for tin plating contact were examined in the case of embossment-plane contact. As experimental results it was found that the friction coefficient is affected by contact force, plating thickness and contact radius. The force dependence of the real contact area estimated by FEM analysis shows that the real contact area occurred by elasto-plastic deformation. A larger contact radius and thicker plating thickness result in a larger friction coefficient, because the real contact area is larger. A heavier force results in a smaller friction coefficient, because the average of the contact pressure is larger. The shear stress, which is estimated from experimental results, is much higher than that of tin metal. This indicates that tin attrition of embossment-plane contact is not the shear of tin metal on tin metal but the shear of tin metal on tin oxide according to the hardness results of the tin oxide layer.

In recent years, development of environment measure cars is an important theme of the earth environment protection and energy saving. Various kinds of hybrid electric vehicles increase the production rapidly. However, the vehicle price is one of the big themes for the hybrid electric vehicle’s growth. High voltage harnesses necessary to connect between hybrid units (inverter to motor, battery) that must be fitted in a limited vehicle space. Especially, high voltage and high current wire harnesses for hybrid electrical vehicle need thicker cross section and higher connection reliability in comparison with wires for 12V.In this paper, we set our goal of the terminal which is proof against vehicle vibration and is possible to apply high and continuous current. We successfully selected the structure and the material and developed the terminal at low cost, which is proof against vehicle vibration and is able to pass over 100A current. The developed terminals are used in Lexus GS450h.

In recent years, there has been increasing demand to miniaturize wiring harness connectors in automobiles due to the increasing volume of electronic equipment and the reduction of the installation space allocated for the electronic equipment in automobiles for the comfort of the passengers. With this demand, contact failure caused by the fretting corrosion is expected to become a serious problem. In this report, we examined micro-structural observations of fretting contacts of two different tin plating thicknesses using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) and so on. Based on the results, we compared the microstructure difference of fretting contact caused by the difference of the tin plating thickness.

It is an important issue to investigate the deterioration state of connectors used in long driven vehicles in order to develop vehicle connectors. There are a few reports that investigated the deterioration state of connectors used in long driven vehicles in detail. Therefore, the deterioration state of a connector collected from a vehicle (driven for 8 years, 100,000km mileage) was investigated through the terminal resistance, the observation of connector surface, and oxidized abrasion powder in this study. Moreover, we investigated temperature environment and vibration status in the actual vehicle environment to identify the main factor of the connector deterioration. From these results, the deterioration of connectors used in long driven vehicles was estimated to be mainly fretting wear caused by vibration. In addition, the fretting cycle of fretting corrosion test in laboratory equivalent to fretting in 8 years 100,000km mileage driven was figured out by comparing the radius of the oxidized abrasion powder in fretting corrosion test with in corrected terminals.

In order to clarify the theory of contact resistance, there are many reports in these years. Mathematically the constriction current is derived from Laplace equation at one contact. And numerical approach for constriction current analysis was also preformed by Minowa and Sawada. Furthermore, as an experimental approach, Sawada et al. are successful in in-situ observation of current constriction inside the contact utilizing the behavior of the wafer for light emitting diodes that light is emitted in the position where the current flows. In this study, we attempted to give consideration to how the constriction resistance changes for the thin film wafer by comparing an experimental method, an analytical method, and theoretical values. As results, it was proved that when the film is as thick as 200µm, both experimental results and analytical results roughly matched with the theoretical values of the constriction resistance. However, when the film gets thinner to 50µm, the constriction resistance was larger than the theoretical values (R=ρ/2a). In addition, the values of contact resistance almost matched with the experimental values. These results determine that contact resistance in the thin film can be calculated using electric field analysis.

Tin plated terminals are widely used for automotive connectors due to low cost and higher reliability. But it is observed that contact resistance of tin plated terminal increased due to fretting corrosion, which is originated from heat cycle or vibration. In order to clarify the degradation of terminal, it is necessary to obtain the contact resistance distribution on fretting corrosion wear of tin plated contact in detail, because the terminal has more than two point of conduction point at least. Thus, the detail measurement of resistance distribution in fretting corrosion wear is performed to estimate contact resistance at mating terminal. As the result, in the region of higher concentration of oxygen measured by EDX analysis, the resistance is tended to be measured higher. And the contact resistance of whole contact wear is estimated by static electric field analysis based on film resistance distribution at contact wear. These analysis results are approximately agreement with the contact resistance on fretting corrosion experimentally. That means the degraded resistance of terminal mating would be estimated using by this technique.

In order to clarify the theory of contact resistance, there are many reports in these years. Mathematically the constriction current is derived from Laplace equation at one contact which shape is circle, ellipse, triangle and square. And numerical approach for constriction current analysis was also preformed by Minowa and Sawada. Although there are many reports on the contact resistance measurement, not many reports on the detailed behavior of current density distribution in the contact area experimentally. Therefore, we attempted to observe the behavior of the current density distribution in the contact by using semiconductor wafers. As a result, it was confirmed that electric current is uniformly distributed over the contact area covered by an oxide film, while it is concentrated at the periphery of the contact if there is no oxide film at contact. And the contact resistance of apparent contact area is almost same as real contact area which is also agree with the theory of multi-spot contact. Moreover, the contact resistance is influenced by wafer thickness.

Adsorbed silicone vapor on contact surfaces decomposes typically to SiO2 by elevated temperature due to discharge or Joule heating. However, even if temperature is lower than decomposition temperature, weak decomposition is induced in very complex states. Namely, silicone molecule has an equilibrium reaction from linear molecular structure to ring structure, or its reverse reaction in the room temperature. Furthermore, in the oxidation process, as the molecular changes various structures and causes imperfect decomposition, and various types of compounds occur. In the present paper, electrical condition of load and occurrence of the failure due to silicone vapor contamination were discussed with practical examples. And it was clarified that various high polymer silicone compounds including liquid are formed by their polymerization in the decomposing process. Furthermore, a mechanism of formation of carbon from the silicon vapor under this process is also discussed.

Theoretically the Laplace equation can be used to calculate the current constriction behavior in electrical contacts. On the actual behavior of current constriction, although there are many reports on the contact resistance measurement, not many reports on the detailed behavior of current density distribution in the contact area experimentally. Therefore, we attempted to observe the behavior of the current density distribution in the contact by using semiconductor wafers in this study. As a result, it was confirmed that electric current is uniformly distributed over the contact area covered by an oxide film, while it is concentrated at the periphery of the contact if there is no oxide film. These results qualitatively agree with the results of the earlier theory and electric field analysis.

It is observed that contact resistance of tin plated contact in automotive connectors increased due to fretting corrosion, which is originated from heat cycle or vibration. In this study, the measurement condition is established to obtain the contact resistance distribution on fretting corrosion trace of tin plated contact in order to clarify the relationship between contact resistance and oxide formation. As the result, in the region of higher concentration of oxygen measured by EDX analysis, the contact resistance is tended to be measured higher. And the contact resistance of whole contact trace is estimated?@by static electric field analysis based on contact resistance distribution at contact trace. These analysis results are approximately agreement with the contact resistance on fretting corrosion experimentally.

For tin plated connector contacts, it was found that friction coefficient of the lubricated contacts was higher than that of non-lubricated contacts. This is very different from common knowledge of lubrication. In this paper, size of true contact areas of static contact condition was discussed by FEM analysis under conditions for both lubricated and non-lubricated contacts between platinum (Pt) hemisphere and tin (Sn) plated flat. In the result, it was clarified that the contact area with lubricant became lager than non-lubricated contacts. This is due to indentation depth of the hemisphere into tin plated layer. Projected area for sliding direction of the sunken contact surface was calculated by geometrical contact model. From these discussions, it was concluded that the increase in friction coefficient with lubricant was not caused by increase in adhesion area but by increase in depth of the contact trace and in plowing the flat.

Tin (Sn)-plated contacts are used in various electrical applications owing to their low cost and stability of contact resistance under a high contact load. At present, such contacts are widely applied in the automotive industry and the other fields. The surface of plated tin is covered with their oxide film such as SnO or SnO2, but it is possible to obtain low contact resistance by applying a high contact load. It is expected that downsized connectors will be developed in future. Therefore, it is important to study contact resistance behavior under a low contact load. In this study, we first review the mechanical deformation phenomena of the tin crystal structure in a contact area under contact loading with respect to the contact resistance behavior, which was presented at IEEE Holm Conference 2008. To clarify these important phenomena, the mechanical stress distribution in the tin-plated layer was numerically analyzed by FEM. It was found that the mechanical stress in the layer propagated to the periphery of the contact area along the radial direction during loading. Therefore, formation of the crystal of the contact area is forced outside of the contact area. Because of the peculiar distribution of the stress, the crystal grains are separated and piled up outside of the contact area. The mechanism of marked decrease in contact resistance during the piling up at the periphery with separation of crystal grains was clarified. This phenomenon is very different from commonly observed decrease in contact resistance due to elastic and plastic deformation.

Tin plating has been applied widely to electrical connectors to save the cost for electromechanical devices. However, the tin plated surface covered with oxide film is fundamentally different from gold plated surfaces. The oxide film prevents the surface from corrosion. When the film is interposed between contact interface, contact resistance increases. It is necessary to break down mechanically to obtain low contact resistance. However, detail study on the oxide film on the tin plated surfaces was not found in literatures. On the other hand, fretting phenomena is very important for connector contacts, particularly, for automotive connectors under vibration. The failure to tin plate is many times from fretting and this is in the literature. In the present study, growth law of the oxide film on the tin plated surface was found by measurement using an ellipsometry for exposure to the atmosphere. Moreover, the film thickness was identified by TEM (Transmission Electron Microscope). The results well agreed with results obtained by the ellipsometry. The initial oxide film formed at temperatures less than 120C° is a mixture of crystalline SnO and an amorphous molecule form of tin oxide. However, the oxide formed on the surface exposed at 120C° was identified as crystal SnO2. As a result, growth of the oxide film showed linear law for the initial stage of the exposure. In the second stage, the oxide film indicated 1/4 law. After this stage, the film growth saturated. The contact resistance indicated low constant value until 10nm in thickness. This low value is due to conduction mechanisms of thin film. For the thicker film than 10nm

Tin (Sn) plated contacts are widely used by acceptable properties of low cost and stability of contact resistance under high contact load as substitution of gold (Au) plated contacts. In the present time, these type contacts are applied to automotives. Surfaces of plated tin are covered with their oxide film, but it is possible to obtain low contact resistance by applying high contact load. Tendency in down size of the connector will increase in the near future. Therefore, it is important to study contacts resistance characteristics under low contact load. In this study, relationships between contact resistance and change of contact traces were examined by the tin plated specimen. It was found that in the contact configuration for hemisphere of platinum and tin plated flat contact, the hemisphere surface sank into the softer tin plated flat surface with increase in contact load. In the results, piling up of the periphery of the contact trace occurs. Moreover, it was found that crystal grains piles up at the periphery of the true contact area. During the piling up of the periphery, sudden decrease in contact resistance was found. This phenomenon is very different from usual decrease in contact resistance due to elastic and plastic deformation.

In recent years, there has been increasing demand to miniaturize wiring harness connectors in automobiles due to the increasing volume of electronic equipment and the reduction of the installation space allocated for the electronic equipment in automobiles for the comfort of the passengers. With this demand, contact failure caused by the fretting corrosion seems to become a serious problem in the future. There are many reports about fretting contact resistance transitions from the low contact resistance level to the high contact resistance level, but there are few reports about observation of the microstructure transition. In our previous study, we conducted observation using SEM, TEM and micro hardness measurement using a nanoindentation tester on low and high contact resistance samples (dimple-flat configuration) under the fixed test conditions (contact load: IN, tin plating thickness:5 mum). In this report, we examined microstructure observation of flat fretting contacts, modifying the tin plating thickness as a parameter. Based on the observation results, we considered the change of the contact microstructure and the difference of the contact resistance rising curve behavior caused by the tin plating thickness.

Recently characteristics required of automobiles have been diversified, and from the electric/electronic points of view, the changes of automobiles are a wide range of electronization flow of control and changes of power source of automobiles represented by electric automobiles and the transmission system. Considering these, the connector, one of the network parts of an automobile to shoulder the transmission of signals and power is increasingly important in electric connection and reliability. In designing the connector to be installed in the automobile, therefore, we think it significant to obtain theory to become a design guide on the connecting performance, especially contact resistance characteristic. The objective of this study is to derive the theoretical formula of the contact resistance to meet the requirements from the design of the connector to be installed in the automobile and verify its effectiveness. First, from the known formula of contact resistance, we derived a formula including parameters to determine the connector specifications that are simple and can be used for the design and verified the effectiveness from statistical results of various measurement data.

We report on the status of the Cassegrain Instrument Automatic Exchanger (CIAX) control system for the Subaru Telescope. Devices controlled by a shell program in the previous version are now controlled by a macro. It can now be operated safely from remote site. Features of the new system are: 1. New macro. The new macro has two features: (1) Action skip. The macro can skip actions that have been executed earlier. It judges whether to skip by checking the status of devices. Resumption of interrupted macro or reversal from halfway of a process is possible. (2) Macro flexibility: The script has every possible sequential action and chooses actions by checking device status. For instance, it can determine whether the cart is at the telescope or at one of the instrument standby flanges and select a proper hookup command. 2. GUI for macro operation and CGI for rewriting setup files. The new GUI uses a commercial instrument control language. A CGI application accesses setup files. 3. Omni-directional Infrared (IR) LAN. Omni-directional IR LAN is being tested for the cart because radio frequency wireless LAN is prohibited on Mauna Kea to avoid interference to radio telescopes. Conventional IR LAN failed because of its directionality. The CIAX system is now routinely used for instrument exchange. For complete automatic operation, there are still a few tasks left, such as macro-controlled instrument shutdown and restarting, standardizing interfaces and procedure for all instruments and further increasing reliability which is higher already compared to conventional manual exchange.

The CIAX system especially CIAX-3 increased observation efficiency for Cassegrain test instruments at the early phase of Subaru telescope test observation. In order to control this system effectively and automatically, a control software for the entire system of the CIAX was developed. The software design goals are (1) redundancy for robust system, (2) the safety of the instrument by interlocking, (3) maximum efficiency by automatic control and (4) easy user interface for operator. In this paper, we describe the software which has been being tested through the telescope and instrument commissioning phase.

The Cassegrain Instrument Automatic eXchanger (CIAX) system for the 8.2 meter Subaru Telescope moves instruments between the Cassegrain mounting flange and stand-by flanges without manual intervention. Observation efficiency improves not only because of quick exchanges, scheduled or emergency, but also because of increased flexibility in selecting an optimum instrument for weather conditions or observation goals. Reliable and safer instrument exchanges are achieved by the precision mechanical positioning system (less than 0.5 mm) and an automatic connector system for electrical cables, optical fibers and fluid lines. Instrument down time due to connector/cable failure by human error is eliminated. Interfaces to the telescope flange are standardized for all five Cassegrain instruments (approximately 2000 kgf each) currently in use or under preparation.

In this study, a thermal barrier (air gap) piston was used to improve the vaporization of methanol in the combustion chamber. The engine operating condition was fixed at 25 rps (1500 rpm) and wide open throttle. The experimental results are follows, (I) the degree of constant volume was improved about 2 % as compared to that of operation without the thermal barrier piston. (2) The indicated thermal efficiency was the same as that of operation with a fully vaporized methanol and air mixure. (3) The variation in maximum pressure and the rate of pressure rise were half that of operation with a liquid methanol and air mixture.

Equations of motion of solid particles in a pump impeller having low specific speed were solved numerically with assumptions of an inviscid and incompressible quasi-three dimensional flow, and the general behavior of solid particles in the pump was clarified. The particle trajectories and forces acting on particles, the diameters of which range from 0.1 to 0.5 mm and the specific-gravities from 1.8 to 5.4 were obtained for different flow capacities. The locations and the velocities, with which the particles impinge on the boundary surface of the pump, were also discussed in order to predict the erosion damage in pumps.