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Effect of normal forces on fretting corrosion of tin-coated electrical contacts
MR-12561; No of Pages 7 Microelectronics Reliability xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel
Review paper
Effect of normal forces on fretting corrosion of tin-coated electrical contacts Dong-Woon Han a, Ho-Kyung Kim b,⁎ a b
Dept. of Automotive Engineering, Graduate School, Seoul National University of Science and Technology, Republic of Korea Dept. of Mechanical and Automotive Engineering, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea
a r t i c l e
i n f o
Article history: Received 15 April 2017 Received in revised form 8 July 2017 Accepted 8 July 2017 Available online xxxx Keywords: Fretting corrosion Electric contact Threshold displacement amplitude Gross slip Partial slip
a b s t r a c t Electrical connectors have been extensively used as the electrical connecting component in various electronic systems. The performance of the electrical connector directly affects the performance of an entire system. Fretting corrosion is generally recognized as an essential failure mechanism for an electrical contact. Major factors affecting the fretting corrosion include current magnitude, normal contact force, displacement amplitude, relative humidity, frequency, and temperature. In order to investigate the effect of normal forces on fretting corrosion behavior, normal forces were fixed at 1 N, 1.25 N, 1.5 N, 2 N, 2.5 N for various displacement amplitudes. Riders and flats made of 0.3 mm-thick brass sheet were coated with tin. The change of the electrical resistance was measured by applying constant current and displacement amplitudes to the upper sphere contact specimen, fixing the flat specimen. The normal force (F) shows a linear relationship with the threshold displacement amplitude (δth). When the displacement amplitude increases with increasing normal force, the plating layer was severely worn due to contact pressure. Dimples were found on the surfaces of the central part of the specimens showing infinite lifetime, suggesting that a soft metal-to-metal contact formed just before separation of the mated specimens at the end of the test. Specimens with an infinite lifetime tested under partial slip condition showed a relatively low oxygen concentration on the center of the wear surface. It is very important to design an electrical connector contact to maintain partial slip by using the information on the normal force and displacement amplitude in order to achieve infinite lifetime. © 2017 Elsevier Ltd. All rights reserved.
Contents 1. 2. 3.
Introduction . . . . . . . . . . . . . . . Experimental procedures . . . . . . . . . Results and discussion . . . . . . . . . . 3.1. Change in contact electrical resistance 3.2. Structural analysis of the specimen . 3.3. SEM observation of damaged surfaces 3.4. Surface analysis . . . . . . . . . . 4. Conclusion . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . .
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1. Introduction Mechanical vibration and thermal expansion and contraction cause micro-displacements between pairs of contact surfaces of automobile connector. When the contact surfaces have oscillatory displacement at ⁎ Corresponding author. E-mail address: [email protected] (H.-K. Kim).
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small sliding amplitude (smaller than 100 μm), electrical insulating oxidation products are continuously generated at the contact surfaces and cause fretting corrosion. When fretting corrosion occurs, signal data values output from various electronic control sensors of the vehicle may be distorted, resulting in malfunction of the electronic devices. Major factors involved in fretting corrosion include current magnitude, normal contact force, displacement amplitude, relative humidity, frequency, temperature, environment gas, etc. [1–6]. Many studies
http://dx.doi.org/10.1016/j.microrel.2017.07.048 0026-2714/© 2017 Elsevier Ltd. All rights reserved.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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D.-W. Han, H.-K. Kim / Microelectronics Reliability xxx (2017) xxx–xxx
have been performed to understand the factors contributing to fretting corrosion lifetimes of electrical connectors. For examples, Fouvry et al. [1] proposed a method to predict the electrical endurance of silver-coated contacts. They formalized the endurance, using a power law function of the mean friction energy density dissipated during a fretting cycle taking into account the normal force, friction coefficient and sliding amplitude. Pascucci [2] et al. proposed a theoretical model for fretting corrosion degradation of non-noble metal coated contacts. They formulated a theoretical model to estimate the resistance rise and oxide accumulation during fretting cycles, adopting a continuum method based on a consideration of a macroscopic description of fretting-oxidation induced evolutions of resistance and metal fraction. Chalandon et al. [3] conducted constant–displacement-amplitude tests to determine the effect of a nickel layer on the performance of electrical tin coated contacts. They reported that there is no influence of the nickel layer on the electrical endurance during gross slip. The application of the nickel layer was reported to cause the maintaining of a high tin tin friction coefficient and to extend the partial slip domain, resulting in an increase of the reliability of the electrical contact. Song et al. [4] investigated the effect of temperature on fretting corrosion of gold-coated contacts. They performed fretting test in the temperature range of 25 °C–125 °C by fixing the displacement amplitude at 25 μm. They reported that the role of gold coating is soften and lubricate the contact surface, resulting in the maintaining of a low contact resistance and in reducing failure rate at higher temperature. At elevated temperatures, however, the formed copper oxide particles deteriorate the contact resistance by wearing the substrate copper alloy material. Lee et al. [5] investigated the effect of temperature on fretting corrosion of lubricated tin-coated contacts. They performed a fretting test in the temperature range of 27 °C–155 °C by fixing a normal force of 0.5 N and displacement amplitude of 90 μm. They reported that, at room temperature, the lubrication is very effective and the contact resistance remains stable. However, at elevated temperatures the performance of lubricated contact is poor due to the higher wear rate of tin coating and also due to evaporation of the lubricant. Vincent et al. [6] investigated the fretting sliding transition from partial slip to gross slip for electrical contacts with noble and non-noble material coatings. They reported that if the displacement amplitude becomes higher than the transition value, the generalized gross slip condition activates debris formation over the whole contact surface, resulting in unstable electrical resistance for non-noble material coatings. Noble material coatings can only extend the lifetime of the electrical contacts. Wearing-out of the substrate coating material caused high and unstable electrical resistance. Vincent et al. [6] also reported that the sliding transition can conveniently be predicted if the cyclic hardening behavior of the mating material and the friction law of the tribo-system can be correctly identified.
Fig. 1. Illustration of the influence of the sliding regime on the finite and infinite behavior of electric connectors.
Fig. 2. Fretting test system.
When two objects come into contact, a micrometer-level sliding motion can occur. For a pair of contact surfaces in spherical form and a plane contact, the sliding regime can be divided according to the displacement amplitude into partial slip and gross slip [7], as shown in Fig. 1. When the displacement amplitude is small, partial slip causes an annular slip area on the outer periphery and a stick zone in the center area where slip does not occur. On the other hand, when the sliding displacement is relatively large, the stick zone disappears and gross slip occurs. Generally, when a partial slip occurs on an electrical contact, an oxide film is formed in the area where the slip occurs. The stick zone in the center has metal-to-metal contact. Therefore, as shown in Fig. 1, the electrical resistance is very low, so that it is possible to achieve an infinite lifetime of the electrical connector terminal. In contrast, when a gross slip occurs, slip occurs over the entire contact area and oxide debris is created in the entire area. As a result, the electrical resistance rapidly increases with the number of cycles, as shown in Fig. 1. It is desirable to design an electrical connector contact to maintain partial slip in order to guarantee its electrical lifetime. The main factors affecting partial slip are normal force and displacement amplitude. Generally, as the normal force increases, the displacement amplitude required for partial slip increases. The purpose of this study is to investigate the effect of the normal force on the electrical resistance through fretting experiment under various displacement amplitude conditions for tin-plated brass connectors. For this purpose, the displacement amplitude required to achieve infinite lifetime at each normal force will be derived. The aim of this study is to provide basic information on the design of the connector in terms of its durability. 2. Experimental procedures In this study, we designed and built a system for the fretting test. The experimental setup is shown in Fig. 2. The system is composed of a displacement generation system, a normal force measuring system, a system for transferring a dead weight to the test specimen, and holders for fixing the specimens. The specimens used for the fretting test were brass plate of 0.3 mm thickness plated with tin. In order to improve the adhesion of the tin plating, tin was electroplated to a thickness of 10 μm after plating the brass very thinly with copper. The upper sphere contact specimen and the lower flat specimen were fixed to the holders. The fretting test was conducted at a frequency of 0.05 Hz. A constant current-resistance measurement method was used to measure the changing electrical contact resistance during the fretting test. As shown in Fig. 3, by supplying a constant current of 0.1 A across the specimen, the voltage was measured
Fig. 3. Schematic of measurement for contact resistance.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
D.-W. Han, H.-K. Kim / Microelectronics Reliability xxx (2017) xxx–xxx
Fig. 4. Variation of contact resistance with fretting cycle at various displacement amplitudes under a normal force of 1 N.
using a high-resolution multimeter (Agilent 34410A) capable of measuring up to 1 nV. 3. Results and discussion 3.1. Change in contact electrical resistance In this study, change of electrical contact resistance was observed at various displacement amplitudes by fixing normal forces of 1 N, 1.25 N, 1.5 N, 2 N, and 2.5 N. Fig. 4 shows the change in electric resistance with the number of fretting cycles at displacement amplitudes of 15 μm, 19 μm, 20 μm, 22 μm and 23 μm and at a normal force of 1 N. It was confirmed that, for all displacement amplitude tests, the contact resistance rapidly decreased after several fretting cycles. This phenomenon is
Fig. 5. Variation of contact resistance with fretting cycle at various displacement amplitudes under a normal force of 1.25 N.
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Fig. 6. Displacement amplitude against number of cycles at a normal force of 2.5 N.
attributed to the electric resistance, which was relatively high (at a level of approximately 0.001 Ω) due to the initial oxide film, which formed on the additional tin coating layer and immediately decreased after fracture of the film. For the tests with displacement amplitudes of 20 μm, 22 μm and 23 μm, the resistance continued to increase after approximately 50 cycles. This behavior can be attributed to the fact that the oxide particles and wear debris accumulated on the contact surface electrically blocked the contact part of the surface, as has been described in other studies [8,9]. Thereafter, a contact resistance peak higher than 0.1 Ω occurred and the resistance changed unstably. However, for the tests with the displacement amplitudes of 15 μm and 19 μm, the contact resistance was stable at a level of approximately 0.001 Ω. Also, the resistance level for the tests with an amplitude of 15 μm was lower than that with an amplitude of 19 μm. This is because the stick zone having metal to metal contact at the amplitude of 15 μm was larger than that at the amplitude of 19 μm, which resulted in a
Fig. 7. Effect of normal force on the threshold displacement amplitude for infinite lifetime.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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Table 1 Summarized FEM results of contact pressure and radius under various loading conditions. Normal force (N)
1
1.25
1.5
2
2.5
Maximum contact pressure (MPa) Contact radius (μm)
87.3 81.5
89.6 89.9
92.3 98.3
97.8 109.3
100.7 121.1
lower electrical resistance. Fig. 4 shows that the displacement amplitude is an important parameter for infinite lifetime or stable electrical resistance at constant normal force. For the shape and size of the specimen at a normal force of 1 N, the critical displacement amplitude for infinite lifetime is 19 μm. Fig. 5 shows changes in electric resistance with number of fretting cycles at various displacement amplitudes under a normal force of 1.25 N. From this figure, it can be seen that the critical displacement amplitude for infinite lifetime is 29 μm, indicating that as the normal force increases, the critical displacement amplitude increases. As the normal force increased by 25% from 1 N to 1.25 N, the magnitude of the critical displacement amplitude increased by 53% from 19 μm to 29 μm, suggesting that critical displacement amplitude was governed by the normal force. For this contact, increase of normal force caused a shift from gross slip to partial slip regime for the same displacement amplitude. Increase of displacement amplitude leads to reduction of the unexposed metal to metal contact surface area, which results in a shorter lifetime of the electrical contact. Therefore, to ensure infinite lifetime of electrical connector in related industries, there is need for a quality control system to keep the contact force constant. Various criteria have been proposed by various researchers regarding the lifetime of electrical contacts [10,11]. Typically, when a contact is used in a particular application area, the user establishes a value of the contact resistance that will interrupt the function of the system. These criteria are different for signal contacts and power contacts, and the standards differ for each company. In this study, on the assumption that the tin-plated connector was used for signal contacts, the failure criterion was set at 0.01 Ω. Fig. 6 shows the relationship between the displacement amplitude and the number of fretting cycles for a normal force of 2.5 N; this curve is similar to the fatigue S-N curve. As shown in Fig. 6, the lifetime was drastically reduced with increasing displacement amplitude at a normal force of 1 N. It can be seen that the slope of the curve is very steep, suggesting that the displacement amplitude is very sensitive to lifetime. Fig. 7 shows the threshold displacement amplitude necessary for infinite lifetime for each normal force. The relationship between the normal force (F) and the threshold displacement amplitude (δth) was found to be δth =38.5F − 20.4. It can be seen that as the normal force increases, the threshold displacement amplitude linearly increases.
Fig. 8. (a) 2-D and (b) 3-D contact pressure distribution of tin coated brass plate under force of 1.5 N.
Table 1. The ratios of the threshold displacement amplitude to the contact radius for each normal force are also summarized in Table 2. Table 2 shows that as the normal force increases from 1 N to 2.5 N, the ratio of the threshold displacement amplitude to the contact radius increases from 0.24 to 0.52. Fig. 8 shows two-dimensional and three-dimensional
3.2. Structural analysis of the specimen The non-linear kinematic hardening elastic-plastic material model was used in the structural analysis to determine the contact radius. A 10 μm tin plating layer was considered. Structural analysis was performed in conjunction with ABAQUS and HyperMesh. In order to apply the contact condition between the upper plate and the lower plate, the upper plate, to which a load is applied, is set as the master; the lower plate, fixed by constraint, is set as a slave; and the coefficient of friction is set at 1.3 [12]. Structural analysis was carried out for normal forces of 1 N, 1.25 N, 1.5 N, 2 N, and 2.5 N. The structural analysis results are summarized in Table 2 Ratio of threshold displacement amplitude to contact radius at various normal forces. Normal force (N)
1
1.25
1.5
2
2.5
δth (μm) δth/a
19 0.23
29 0.32
33 0.34
60 0.55
75 0.62
Fig. 9. Threshold displacement amplitude as a function of average contact pressure.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
D.-W. Han, H.-K. Kim / Microelectronics Reliability xxx (2017) xxx–xxx
distributions of the pressure at a normal force of 1.5 N. As a result, the contact radius was found to be 98.3 μm and the maximum contact pressure was 92.3 MPa. As shown in Fig. 8, the pressure tends to increase rapidly at the end of contacts of the upper and lower test specimens. The abrupt increase of pressure is considered to be due to a pile-up phenomenon in which contacts form because the specimen is plated with very soft tin. The average contact pressure was determined by dividing the normal force by the contact area. The relationship between the threshold displacement amplitude (δth) and the average contact pressure (pave) is δth = 8.4pave − 381.8 (in MPa, μm), as shown in Fig. 9. The threshold displacement amplitude is linearly proportional to the average pressure. Therefore, it is desirable to increase the contact pressure as much as possible within the maximum limit of the insertion force in order to achieve infinite lifetime of the connector terminal. It is also possible to derive the threshold displacement amplitude necessary for infinite
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lifetime by using the average contact pressure. However, to apply this relation between the threshold displacement amplitude (δth) and the average contact pressure (pave) for infinite lifetime of electrical contacts, further study will be needed on the possibility of applying this relation for various shapes of tin plating contacts. 3.3. SEM observation of damaged surfaces The areas of fretting contact wear on the flat specimens at various displacement amplitudes were observed using SEM. Fig. 10 shows the fretting wear surface at a normal force of 1 N at displacement amplitudes of 15 μm, 18 μm, 19 μm, 20 μm, 22 μm and 24 μm. These figures show that build-up of tin and oxide debris having sizes in a range from several micrometers to 100 μm or more on the contact damaged area. In the case of the specimen at a displacement amplitude of 15 μm, as shown in Fig. 10(a), there is a trace of a slightly smeared layer
Fig. 10. SEM micrographs of the fretting surfaces of the specimens with displacement amplitudes of (a) 15 μm, (b) 18 μm, (c) 19 μm, (d) 20 μm, (e) 22 μm and (f) 24 μm under a normal force of 1 N.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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Fig. 11. SEM micrographs of the fretting wear surfaces and EDS results of specimens with (a) displacement amplitude of 19 μm and (b) displacement amplitude of 24 μm at normal force of 1 N.
on the left side of the figure, but there is relatively less slip and wear around the contact damaged area. In addition, dimples were found on the surface of the central part of the specimen. This suggests a soft metal-to-metal contact formed just before separating the mated specimens at the end of the test. However, as the displacement amplitude increased, more wear occurred, and the plating tin layer became worn, build-up occurred around the contact area and oxide debris scattered. This observation indicates that the electric resistance increased due to the oxide debris. Also, from the observation of SEM figures of the specimens tested at various normal forces, it was confirmed that when the displacement amplitude increased as the normal force increased, the plating layer was severely worn due to contact pressure. 3.4. Surface analysis The contact damaged surface caused by the fretting was analyzed by energy dispersive spectroscopy (EDS) installed on the SEM. Fig. 11(a) and (b) show the fretting wear surfaces and analytical results of the
specimens tested at 19 μm and 25 μm displacement amplitudes, respectively, having infinite lifetime and finite lifetime at normal force of 1 N. As a result of the EDS measurement of the displacement amplitude of tested 19 μm specimen, the point marked 3 in the damaged area shows high tin concentration and low oxygen concentration, indicating that this point had metal-to-metal contact during the fretting test. It can be thought that this point caused the very low and stable electrical resistance, which resulted in an infinite lifetime of this specimen. The other measurement points, due to their relatively high oxygen concentration, are considered to be oxide films or debris. For the test specimens with a displacement amplitude of 24 μm, the concentration of oxygen was relatively high for points 1, 2 and 3. Point 4 near the contact area without fretting contact shows a relatively low concentration of oxygen. In the case of the specimen with a displacement amplitude of 24 μm, most points, including the center, showed relatively high concentration of oxygen due to the oxide film or oxide debris. These materials cause an increase in the electric resistance, resulting in a finite lifetime.
Table 3 Comparisons of oxygen contents at the center of the surface for specimens tested at critical displacement amplitude and at larger than critical displacement amplitude under various normal forces.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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Table 3 summarizes the oxygen and tin concentrations of the tested specimens showing infinite and finite lifetimes for each normal force. Table 3 shows that the specimens tested at the threshold displacement amplitude had a relatively low concentration of oxygen near the center of the wear surface. This suggests that the tested specimen had metalto-metal contact. In other words, the observations prove that partial slip occurred in these specimens. And the specimens show the oxygen concentration of approximately 29% on average. However, due to oxide debris and film, the specimens tested at amplitudes larger than the threshold displacement amplitude showed an increase in the oxygen concentration of approximately 72% on average at the fretted surface. The oxide film or debris caused high electric resistance, suggesting that gross slip occurred for these specimens. Conclusively, the electrical resistance evolution is shown to be mainly controlled by the displacement amplitude and normal force. It has been confirmed that below a threshold displacement amplitude, associated with a partial slip condition where a sticking zone is maintained within the contact, the electrical endurance has infinite lifetime. Under a partial slip condition, direct metal-to-metal contacts are generated in the sticking zone and exhibit low and stable contact resistance. Dimples are generally formed by soft metal-to-metal separation or soft metal fracture. Flat and cleavage fracture surfaces are generally formed only by brittle metal fracture such as metal-to-oxide films fracture. Therefore, if the contact point has soft metal-to-metal contact before separating the mated the specimens, dimples can be observed in the sticking zone. This can explain why the specimen with dimples on the surfaces experienced a partial slip during fretting and exhibits low oxygen concentration, which resulted in infinite lifetimes. Above this threshold, when gross slip conditions are operating, a finite lifetime is observed. The presence of dispersed tin oxide debris having a relatively high oxygen concentration can sufficiently separate the two specimens contact surfaces and cause a sharp increase in the electrical contact resistance. And, it is shown that as the normal force increases, the displacement amplitude required for partial slip increases. Or, as the displacement amplitude decreases, the normal force required for partial slip decreases. Finally, in order to achieve an infinite lifetime of the electric connector, it is very important to maintain partial slip using the basic information on the normal force and displacement amplitude. 4. Conclusion Fretting corrosion is generally recognized as an essential failure mechanism for an electrical contact. Major factors affecting fretting corrosion are current magnitude, normal contact force, displacement amplitude, relative humidity, frequency, and temperature. In order to analyze the effect of the normal force on the fretting corrosion of electrical connector contacts, normal forces were fixed at 1 N, 1.25 N, 1.5 N, 2 N, 2.5 N for various displacement amplitudes. The change of the electrical resistance was measured by applying constant current and displacement amplitudes to the upper sphere contact specimen, fixing the flat specimen. Assuming that the number of fretting cycles
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corresponding to electric resistance of 0.01 Ω indicates the failure lifetime, and that an infinite lifetime is 105 cycles, the normal force (F) shows a linear relationship with the threshold displacement amplitude (δth) as follows; δth = 38.5F − 20.4. The relationship between the average contact pressure (pave) and the threshold displacement amplitude (δth) is δth = 8.4pave − 381.8 (in MPa, μm), indicating that the threshold displacement amplitude is linearly proportional the average contact pressure. When the displacement amplitude increases with increasing contact load, it is confirmed that the plating layer is severely worn due to contact pressure. In addition, at each normal force, dimples were found on the surfaces of the central part of the specimens showing infinite lifetime. This suggests a soft metal-to-metal contact formed just before separation of the mated specimens at the end of the test. Specimens with an infinite lifetime tested under partial slip condition showed a relatively low oxygen concentration of approximately 29% on the center of the wear surface, but specimens with finite lifetime tested under gross slip showed oxygen concentration of approximately 72% due to the presence of oxide film or debris, resulting in an increment of the electric resistance. Finally, in order to achieve infinite lifetime of the electric connector, it is very important to maintain partial slip by using the basic information on the normal force and displacement amplitude.
Acknowledgments This study was supported by the Research Program funded by SeoulTech (Seoul National University of Science and Technology). References [1] J. Laporte, O. Perrinet, S. Fouvry, Prediction of the electrical contact resistance endurance of silver-plated coatings subject to fretting wear using a friction energy density approach, Wear 330-333 (2015) 170–181. [2] X.Y. Ji, Y.P. Wu, B.H. Lu, V.C. Pascucci, Fretting corrosion degradation of non-noble metal coated contact surfaces: a theoretical model, Tribol. Int. 97 (2016) 31–37. [3] P. Jedrzejczyk, S. Chad, S. Fouvry, P. Chalandon, Impact of the nickel interlayer on the electrical resistance of tin–tin interface submitted to fretting loading, Surf. Coat. Technol. 203 (2009) 1624–1628. [4] W. Ren, P. Wang, Y. Fu, C. Pan, J. Song, Effects of temperature on fretting corrosion behaviors of gold-plated copper alloy electrical contacts, Tribol. Int. 83 (2015) 1–11. [5] T.S.N.S. Narayanan, Y.W. Park, K.Y. Lee, Fretting corrosion of lubricated tin plated copper alloy contacts: effect of temperature, Tribol. Int. 41 (2008) 87–102. [6] S. Hannel, S. Fouvry, Ph. Kapsa, L. Vincent, The fretting sliding transition as a criterion for electrical contact performance, Wear 249 (2001) 761–770. [7] S. Fouvry, Ph. Kapsa, L. Vincent, Analysis of sliding behaviour for fretting loadings: determination of transition criteria, Wear 185 (1995) 35–46. [8] A. Antler, Electrical effects of fretting connector contact materials: a review, Wear 106 (1985) 5–33. [9] Y.W. Park, T.S.N.S. Narayanan, K.Y. Lee, Effect of fretting amplitude and frequency on the fretting corrosion behaviour of tin plated contacts, Surf. Coat. Technol. 201 (2006) 2181–2192. [10] J.H. Whitley, R.D. Malucci, Contact resistance failure criteria, Proc. 9th Int. Conf. Elect. Contact Phenom. 24th IEEE Holm Conf 1978, pp. 111–116. [11] R.S. Mroczkowski, Electronic Connector Handbook, McGraw-Hill, New York, 1998. [12] D.H. Buckley, Friction and Wear of Tin and Tin Alloys From −100 °C to 150 °CNASA TN D-8004 1975.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
Contents lists available at ScienceDirect
Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel
Review paper
Effect of normal forces on fretting corrosion of tin-coated electrical contacts Dong-Woon Han a, Ho-Kyung Kim b,⁎ a b
Dept. of Automotive Engineering, Graduate School, Seoul National University of Science and Technology, Republic of Korea Dept. of Mechanical and Automotive Engineering, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea
a r t i c l e
i n f o
Article history: Received 15 April 2017 Received in revised form 8 July 2017 Accepted 8 July 2017 Available online xxxx Keywords: Fretting corrosion Electric contact Threshold displacement amplitude Gross slip Partial slip
a b s t r a c t Electrical connectors have been extensively used as the electrical connecting component in various electronic systems. The performance of the electrical connector directly affects the performance of an entire system. Fretting corrosion is generally recognized as an essential failure mechanism for an electrical contact. Major factors affecting the fretting corrosion include current magnitude, normal contact force, displacement amplitude, relative humidity, frequency, and temperature. In order to investigate the effect of normal forces on fretting corrosion behavior, normal forces were fixed at 1 N, 1.25 N, 1.5 N, 2 N, 2.5 N for various displacement amplitudes. Riders and flats made of 0.3 mm-thick brass sheet were coated with tin. The change of the electrical resistance was measured by applying constant current and displacement amplitudes to the upper sphere contact specimen, fixing the flat specimen. The normal force (F) shows a linear relationship with the threshold displacement amplitude (δth). When the displacement amplitude increases with increasing normal force, the plating layer was severely worn due to contact pressure. Dimples were found on the surfaces of the central part of the specimens showing infinite lifetime, suggesting that a soft metal-to-metal contact formed just before separation of the mated specimens at the end of the test. Specimens with an infinite lifetime tested under partial slip condition showed a relatively low oxygen concentration on the center of the wear surface. It is very important to design an electrical connector contact to maintain partial slip by using the information on the normal force and displacement amplitude in order to achieve infinite lifetime. © 2017 Elsevier Ltd. All rights reserved.
Contents 1. 2. 3.
Introduction . . . . . . . . . . . . . . . Experimental procedures . . . . . . . . . Results and discussion . . . . . . . . . . 3.1. Change in contact electrical resistance 3.2. Structural analysis of the specimen . 3.3. SEM observation of damaged surfaces 3.4. Surface analysis . . . . . . . . . . 4. Conclusion . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . .
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1. Introduction Mechanical vibration and thermal expansion and contraction cause micro-displacements between pairs of contact surfaces of automobile connector. When the contact surfaces have oscillatory displacement at ⁎ Corresponding author. E-mail address: [email protected] (H.-K. Kim).
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small sliding amplitude (smaller than 100 μm), electrical insulating oxidation products are continuously generated at the contact surfaces and cause fretting corrosion. When fretting corrosion occurs, signal data values output from various electronic control sensors of the vehicle may be distorted, resulting in malfunction of the electronic devices. Major factors involved in fretting corrosion include current magnitude, normal contact force, displacement amplitude, relative humidity, frequency, temperature, environment gas, etc. [1–6]. Many studies
http://dx.doi.org/10.1016/j.microrel.2017.07.048 0026-2714/© 2017 Elsevier Ltd. All rights reserved.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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have been performed to understand the factors contributing to fretting corrosion lifetimes of electrical connectors. For examples, Fouvry et al. [1] proposed a method to predict the electrical endurance of silver-coated contacts. They formalized the endurance, using a power law function of the mean friction energy density dissipated during a fretting cycle taking into account the normal force, friction coefficient and sliding amplitude. Pascucci [2] et al. proposed a theoretical model for fretting corrosion degradation of non-noble metal coated contacts. They formulated a theoretical model to estimate the resistance rise and oxide accumulation during fretting cycles, adopting a continuum method based on a consideration of a macroscopic description of fretting-oxidation induced evolutions of resistance and metal fraction. Chalandon et al. [3] conducted constant–displacement-amplitude tests to determine the effect of a nickel layer on the performance of electrical tin coated contacts. They reported that there is no influence of the nickel layer on the electrical endurance during gross slip. The application of the nickel layer was reported to cause the maintaining of a high tin tin friction coefficient and to extend the partial slip domain, resulting in an increase of the reliability of the electrical contact. Song et al. [4] investigated the effect of temperature on fretting corrosion of gold-coated contacts. They performed fretting test in the temperature range of 25 °C–125 °C by fixing the displacement amplitude at 25 μm. They reported that the role of gold coating is soften and lubricate the contact surface, resulting in the maintaining of a low contact resistance and in reducing failure rate at higher temperature. At elevated temperatures, however, the formed copper oxide particles deteriorate the contact resistance by wearing the substrate copper alloy material. Lee et al. [5] investigated the effect of temperature on fretting corrosion of lubricated tin-coated contacts. They performed a fretting test in the temperature range of 27 °C–155 °C by fixing a normal force of 0.5 N and displacement amplitude of 90 μm. They reported that, at room temperature, the lubrication is very effective and the contact resistance remains stable. However, at elevated temperatures the performance of lubricated contact is poor due to the higher wear rate of tin coating and also due to evaporation of the lubricant. Vincent et al. [6] investigated the fretting sliding transition from partial slip to gross slip for electrical contacts with noble and non-noble material coatings. They reported that if the displacement amplitude becomes higher than the transition value, the generalized gross slip condition activates debris formation over the whole contact surface, resulting in unstable electrical resistance for non-noble material coatings. Noble material coatings can only extend the lifetime of the electrical contacts. Wearing-out of the substrate coating material caused high and unstable electrical resistance. Vincent et al. [6] also reported that the sliding transition can conveniently be predicted if the cyclic hardening behavior of the mating material and the friction law of the tribo-system can be correctly identified.
Fig. 1. Illustration of the influence of the sliding regime on the finite and infinite behavior of electric connectors.
Fig. 2. Fretting test system.
When two objects come into contact, a micrometer-level sliding motion can occur. For a pair of contact surfaces in spherical form and a plane contact, the sliding regime can be divided according to the displacement amplitude into partial slip and gross slip [7], as shown in Fig. 1. When the displacement amplitude is small, partial slip causes an annular slip area on the outer periphery and a stick zone in the center area where slip does not occur. On the other hand, when the sliding displacement is relatively large, the stick zone disappears and gross slip occurs. Generally, when a partial slip occurs on an electrical contact, an oxide film is formed in the area where the slip occurs. The stick zone in the center has metal-to-metal contact. Therefore, as shown in Fig. 1, the electrical resistance is very low, so that it is possible to achieve an infinite lifetime of the electrical connector terminal. In contrast, when a gross slip occurs, slip occurs over the entire contact area and oxide debris is created in the entire area. As a result, the electrical resistance rapidly increases with the number of cycles, as shown in Fig. 1. It is desirable to design an electrical connector contact to maintain partial slip in order to guarantee its electrical lifetime. The main factors affecting partial slip are normal force and displacement amplitude. Generally, as the normal force increases, the displacement amplitude required for partial slip increases. The purpose of this study is to investigate the effect of the normal force on the electrical resistance through fretting experiment under various displacement amplitude conditions for tin-plated brass connectors. For this purpose, the displacement amplitude required to achieve infinite lifetime at each normal force will be derived. The aim of this study is to provide basic information on the design of the connector in terms of its durability. 2. Experimental procedures In this study, we designed and built a system for the fretting test. The experimental setup is shown in Fig. 2. The system is composed of a displacement generation system, a normal force measuring system, a system for transferring a dead weight to the test specimen, and holders for fixing the specimens. The specimens used for the fretting test were brass plate of 0.3 mm thickness plated with tin. In order to improve the adhesion of the tin plating, tin was electroplated to a thickness of 10 μm after plating the brass very thinly with copper. The upper sphere contact specimen and the lower flat specimen were fixed to the holders. The fretting test was conducted at a frequency of 0.05 Hz. A constant current-resistance measurement method was used to measure the changing electrical contact resistance during the fretting test. As shown in Fig. 3, by supplying a constant current of 0.1 A across the specimen, the voltage was measured
Fig. 3. Schematic of measurement for contact resistance.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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Fig. 4. Variation of contact resistance with fretting cycle at various displacement amplitudes under a normal force of 1 N.
using a high-resolution multimeter (Agilent 34410A) capable of measuring up to 1 nV. 3. Results and discussion 3.1. Change in contact electrical resistance In this study, change of electrical contact resistance was observed at various displacement amplitudes by fixing normal forces of 1 N, 1.25 N, 1.5 N, 2 N, and 2.5 N. Fig. 4 shows the change in electric resistance with the number of fretting cycles at displacement amplitudes of 15 μm, 19 μm, 20 μm, 22 μm and 23 μm and at a normal force of 1 N. It was confirmed that, for all displacement amplitude tests, the contact resistance rapidly decreased after several fretting cycles. This phenomenon is
Fig. 5. Variation of contact resistance with fretting cycle at various displacement amplitudes under a normal force of 1.25 N.
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Fig. 6. Displacement amplitude against number of cycles at a normal force of 2.5 N.
attributed to the electric resistance, which was relatively high (at a level of approximately 0.001 Ω) due to the initial oxide film, which formed on the additional tin coating layer and immediately decreased after fracture of the film. For the tests with displacement amplitudes of 20 μm, 22 μm and 23 μm, the resistance continued to increase after approximately 50 cycles. This behavior can be attributed to the fact that the oxide particles and wear debris accumulated on the contact surface electrically blocked the contact part of the surface, as has been described in other studies [8,9]. Thereafter, a contact resistance peak higher than 0.1 Ω occurred and the resistance changed unstably. However, for the tests with the displacement amplitudes of 15 μm and 19 μm, the contact resistance was stable at a level of approximately 0.001 Ω. Also, the resistance level for the tests with an amplitude of 15 μm was lower than that with an amplitude of 19 μm. This is because the stick zone having metal to metal contact at the amplitude of 15 μm was larger than that at the amplitude of 19 μm, which resulted in a
Fig. 7. Effect of normal force on the threshold displacement amplitude for infinite lifetime.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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Table 1 Summarized FEM results of contact pressure and radius under various loading conditions. Normal force (N)
1
1.25
1.5
2
2.5
Maximum contact pressure (MPa) Contact radius (μm)
87.3 81.5
89.6 89.9
92.3 98.3
97.8 109.3
100.7 121.1
lower electrical resistance. Fig. 4 shows that the displacement amplitude is an important parameter for infinite lifetime or stable electrical resistance at constant normal force. For the shape and size of the specimen at a normal force of 1 N, the critical displacement amplitude for infinite lifetime is 19 μm. Fig. 5 shows changes in electric resistance with number of fretting cycles at various displacement amplitudes under a normal force of 1.25 N. From this figure, it can be seen that the critical displacement amplitude for infinite lifetime is 29 μm, indicating that as the normal force increases, the critical displacement amplitude increases. As the normal force increased by 25% from 1 N to 1.25 N, the magnitude of the critical displacement amplitude increased by 53% from 19 μm to 29 μm, suggesting that critical displacement amplitude was governed by the normal force. For this contact, increase of normal force caused a shift from gross slip to partial slip regime for the same displacement amplitude. Increase of displacement amplitude leads to reduction of the unexposed metal to metal contact surface area, which results in a shorter lifetime of the electrical contact. Therefore, to ensure infinite lifetime of electrical connector in related industries, there is need for a quality control system to keep the contact force constant. Various criteria have been proposed by various researchers regarding the lifetime of electrical contacts [10,11]. Typically, when a contact is used in a particular application area, the user establishes a value of the contact resistance that will interrupt the function of the system. These criteria are different for signal contacts and power contacts, and the standards differ for each company. In this study, on the assumption that the tin-plated connector was used for signal contacts, the failure criterion was set at 0.01 Ω. Fig. 6 shows the relationship between the displacement amplitude and the number of fretting cycles for a normal force of 2.5 N; this curve is similar to the fatigue S-N curve. As shown in Fig. 6, the lifetime was drastically reduced with increasing displacement amplitude at a normal force of 1 N. It can be seen that the slope of the curve is very steep, suggesting that the displacement amplitude is very sensitive to lifetime. Fig. 7 shows the threshold displacement amplitude necessary for infinite lifetime for each normal force. The relationship between the normal force (F) and the threshold displacement amplitude (δth) was found to be δth =38.5F − 20.4. It can be seen that as the normal force increases, the threshold displacement amplitude linearly increases.
Fig. 8. (a) 2-D and (b) 3-D contact pressure distribution of tin coated brass plate under force of 1.5 N.
Table 1. The ratios of the threshold displacement amplitude to the contact radius for each normal force are also summarized in Table 2. Table 2 shows that as the normal force increases from 1 N to 2.5 N, the ratio of the threshold displacement amplitude to the contact radius increases from 0.24 to 0.52. Fig. 8 shows two-dimensional and three-dimensional
3.2. Structural analysis of the specimen The non-linear kinematic hardening elastic-plastic material model was used in the structural analysis to determine the contact radius. A 10 μm tin plating layer was considered. Structural analysis was performed in conjunction with ABAQUS and HyperMesh. In order to apply the contact condition between the upper plate and the lower plate, the upper plate, to which a load is applied, is set as the master; the lower plate, fixed by constraint, is set as a slave; and the coefficient of friction is set at 1.3 [12]. Structural analysis was carried out for normal forces of 1 N, 1.25 N, 1.5 N, 2 N, and 2.5 N. The structural analysis results are summarized in Table 2 Ratio of threshold displacement amplitude to contact radius at various normal forces. Normal force (N)
1
1.25
1.5
2
2.5
δth (μm) δth/a
19 0.23
29 0.32
33 0.34
60 0.55
75 0.62
Fig. 9. Threshold displacement amplitude as a function of average contact pressure.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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distributions of the pressure at a normal force of 1.5 N. As a result, the contact radius was found to be 98.3 μm and the maximum contact pressure was 92.3 MPa. As shown in Fig. 8, the pressure tends to increase rapidly at the end of contacts of the upper and lower test specimens. The abrupt increase of pressure is considered to be due to a pile-up phenomenon in which contacts form because the specimen is plated with very soft tin. The average contact pressure was determined by dividing the normal force by the contact area. The relationship between the threshold displacement amplitude (δth) and the average contact pressure (pave) is δth = 8.4pave − 381.8 (in MPa, μm), as shown in Fig. 9. The threshold displacement amplitude is linearly proportional to the average pressure. Therefore, it is desirable to increase the contact pressure as much as possible within the maximum limit of the insertion force in order to achieve infinite lifetime of the connector terminal. It is also possible to derive the threshold displacement amplitude necessary for infinite
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lifetime by using the average contact pressure. However, to apply this relation between the threshold displacement amplitude (δth) and the average contact pressure (pave) for infinite lifetime of electrical contacts, further study will be needed on the possibility of applying this relation for various shapes of tin plating contacts. 3.3. SEM observation of damaged surfaces The areas of fretting contact wear on the flat specimens at various displacement amplitudes were observed using SEM. Fig. 10 shows the fretting wear surface at a normal force of 1 N at displacement amplitudes of 15 μm, 18 μm, 19 μm, 20 μm, 22 μm and 24 μm. These figures show that build-up of tin and oxide debris having sizes in a range from several micrometers to 100 μm or more on the contact damaged area. In the case of the specimen at a displacement amplitude of 15 μm, as shown in Fig. 10(a), there is a trace of a slightly smeared layer
Fig. 10. SEM micrographs of the fretting surfaces of the specimens with displacement amplitudes of (a) 15 μm, (b) 18 μm, (c) 19 μm, (d) 20 μm, (e) 22 μm and (f) 24 μm under a normal force of 1 N.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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Fig. 11. SEM micrographs of the fretting wear surfaces and EDS results of specimens with (a) displacement amplitude of 19 μm and (b) displacement amplitude of 24 μm at normal force of 1 N.
on the left side of the figure, but there is relatively less slip and wear around the contact damaged area. In addition, dimples were found on the surface of the central part of the specimen. This suggests a soft metal-to-metal contact formed just before separating the mated specimens at the end of the test. However, as the displacement amplitude increased, more wear occurred, and the plating tin layer became worn, build-up occurred around the contact area and oxide debris scattered. This observation indicates that the electric resistance increased due to the oxide debris. Also, from the observation of SEM figures of the specimens tested at various normal forces, it was confirmed that when the displacement amplitude increased as the normal force increased, the plating layer was severely worn due to contact pressure. 3.4. Surface analysis The contact damaged surface caused by the fretting was analyzed by energy dispersive spectroscopy (EDS) installed on the SEM. Fig. 11(a) and (b) show the fretting wear surfaces and analytical results of the
specimens tested at 19 μm and 25 μm displacement amplitudes, respectively, having infinite lifetime and finite lifetime at normal force of 1 N. As a result of the EDS measurement of the displacement amplitude of tested 19 μm specimen, the point marked 3 in the damaged area shows high tin concentration and low oxygen concentration, indicating that this point had metal-to-metal contact during the fretting test. It can be thought that this point caused the very low and stable electrical resistance, which resulted in an infinite lifetime of this specimen. The other measurement points, due to their relatively high oxygen concentration, are considered to be oxide films or debris. For the test specimens with a displacement amplitude of 24 μm, the concentration of oxygen was relatively high for points 1, 2 and 3. Point 4 near the contact area without fretting contact shows a relatively low concentration of oxygen. In the case of the specimen with a displacement amplitude of 24 μm, most points, including the center, showed relatively high concentration of oxygen due to the oxide film or oxide debris. These materials cause an increase in the electric resistance, resulting in a finite lifetime.
Table 3 Comparisons of oxygen contents at the center of the surface for specimens tested at critical displacement amplitude and at larger than critical displacement amplitude under various normal forces.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048
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Table 3 summarizes the oxygen and tin concentrations of the tested specimens showing infinite and finite lifetimes for each normal force. Table 3 shows that the specimens tested at the threshold displacement amplitude had a relatively low concentration of oxygen near the center of the wear surface. This suggests that the tested specimen had metalto-metal contact. In other words, the observations prove that partial slip occurred in these specimens. And the specimens show the oxygen concentration of approximately 29% on average. However, due to oxide debris and film, the specimens tested at amplitudes larger than the threshold displacement amplitude showed an increase in the oxygen concentration of approximately 72% on average at the fretted surface. The oxide film or debris caused high electric resistance, suggesting that gross slip occurred for these specimens. Conclusively, the electrical resistance evolution is shown to be mainly controlled by the displacement amplitude and normal force. It has been confirmed that below a threshold displacement amplitude, associated with a partial slip condition where a sticking zone is maintained within the contact, the electrical endurance has infinite lifetime. Under a partial slip condition, direct metal-to-metal contacts are generated in the sticking zone and exhibit low and stable contact resistance. Dimples are generally formed by soft metal-to-metal separation or soft metal fracture. Flat and cleavage fracture surfaces are generally formed only by brittle metal fracture such as metal-to-oxide films fracture. Therefore, if the contact point has soft metal-to-metal contact before separating the mated the specimens, dimples can be observed in the sticking zone. This can explain why the specimen with dimples on the surfaces experienced a partial slip during fretting and exhibits low oxygen concentration, which resulted in infinite lifetimes. Above this threshold, when gross slip conditions are operating, a finite lifetime is observed. The presence of dispersed tin oxide debris having a relatively high oxygen concentration can sufficiently separate the two specimens contact surfaces and cause a sharp increase in the electrical contact resistance. And, it is shown that as the normal force increases, the displacement amplitude required for partial slip increases. Or, as the displacement amplitude decreases, the normal force required for partial slip decreases. Finally, in order to achieve an infinite lifetime of the electric connector, it is very important to maintain partial slip using the basic information on the normal force and displacement amplitude. 4. Conclusion Fretting corrosion is generally recognized as an essential failure mechanism for an electrical contact. Major factors affecting fretting corrosion are current magnitude, normal contact force, displacement amplitude, relative humidity, frequency, and temperature. In order to analyze the effect of the normal force on the fretting corrosion of electrical connector contacts, normal forces were fixed at 1 N, 1.25 N, 1.5 N, 2 N, 2.5 N for various displacement amplitudes. The change of the electrical resistance was measured by applying constant current and displacement amplitudes to the upper sphere contact specimen, fixing the flat specimen. Assuming that the number of fretting cycles
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corresponding to electric resistance of 0.01 Ω indicates the failure lifetime, and that an infinite lifetime is 105 cycles, the normal force (F) shows a linear relationship with the threshold displacement amplitude (δth) as follows; δth = 38.5F − 20.4. The relationship between the average contact pressure (pave) and the threshold displacement amplitude (δth) is δth = 8.4pave − 381.8 (in MPa, μm), indicating that the threshold displacement amplitude is linearly proportional the average contact pressure. When the displacement amplitude increases with increasing contact load, it is confirmed that the plating layer is severely worn due to contact pressure. In addition, at each normal force, dimples were found on the surfaces of the central part of the specimens showing infinite lifetime. This suggests a soft metal-to-metal contact formed just before separation of the mated specimens at the end of the test. Specimens with an infinite lifetime tested under partial slip condition showed a relatively low oxygen concentration of approximately 29% on the center of the wear surface, but specimens with finite lifetime tested under gross slip showed oxygen concentration of approximately 72% due to the presence of oxide film or debris, resulting in an increment of the electric resistance. Finally, in order to achieve infinite lifetime of the electric connector, it is very important to maintain partial slip by using the basic information on the normal force and displacement amplitude.
Acknowledgments This study was supported by the Research Program funded by SeoulTech (Seoul National University of Science and Technology). References [1] J. Laporte, O. Perrinet, S. Fouvry, Prediction of the electrical contact resistance endurance of silver-plated coatings subject to fretting wear using a friction energy density approach, Wear 330-333 (2015) 170–181. [2] X.Y. Ji, Y.P. Wu, B.H. Lu, V.C. Pascucci, Fretting corrosion degradation of non-noble metal coated contact surfaces: a theoretical model, Tribol. Int. 97 (2016) 31–37. [3] P. Jedrzejczyk, S. Chad, S. Fouvry, P. Chalandon, Impact of the nickel interlayer on the electrical resistance of tin–tin interface submitted to fretting loading, Surf. Coat. Technol. 203 (2009) 1624–1628. [4] W. Ren, P. Wang, Y. Fu, C. Pan, J. Song, Effects of temperature on fretting corrosion behaviors of gold-plated copper alloy electrical contacts, Tribol. Int. 83 (2015) 1–11. [5] T.S.N.S. Narayanan, Y.W. Park, K.Y. Lee, Fretting corrosion of lubricated tin plated copper alloy contacts: effect of temperature, Tribol. Int. 41 (2008) 87–102. [6] S. Hannel, S. Fouvry, Ph. Kapsa, L. Vincent, The fretting sliding transition as a criterion for electrical contact performance, Wear 249 (2001) 761–770. [7] S. Fouvry, Ph. Kapsa, L. Vincent, Analysis of sliding behaviour for fretting loadings: determination of transition criteria, Wear 185 (1995) 35–46. [8] A. Antler, Electrical effects of fretting connector contact materials: a review, Wear 106 (1985) 5–33. [9] Y.W. Park, T.S.N.S. Narayanan, K.Y. Lee, Effect of fretting amplitude and frequency on the fretting corrosion behaviour of tin plated contacts, Surf. Coat. Technol. 201 (2006) 2181–2192. [10] J.H. Whitley, R.D. Malucci, Contact resistance failure criteria, Proc. 9th Int. Conf. Elect. Contact Phenom. 24th IEEE Holm Conf 1978, pp. 111–116. [11] R.S. Mroczkowski, Electronic Connector Handbook, McGraw-Hill, New York, 1998. [12] D.H. Buckley, Friction and Wear of Tin and Tin Alloys From −100 °C to 150 °CNASA TN D-8004 1975.
Please cite this article as: D.-W. Han, H.-K. Kim, Effect of normal forces on fretting corrosion of tin-coated electrical contacts, Microelectronics Reliability (2017), http://dx.doi.org/10.1016/j.microrel.2017.07.048