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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.

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.

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.