The 47th IEEE HOLM conference on electrical contacts,
held 10-12 September 2001 in Montreal
The conference had about 150 participants, as usual from three different fields: switching contacts, stationary connector contacts and sliding contacts.
The number of papers was 42; they can be divided in 24 papers on switching, 14 on stationary contacts, 4 on sliding contacts.
On the subject of stationary contacts and connectors the most favorite subjects are high frequency properties, fretting and lubrication, there are no papers on contact physics fundamentals,.
Several papers discussed and/or employed a Digital Scanning Laser Microscope to provide images from contact surfaces. The advantages of this method are that it does not require a vacuum or a conductive surface and that a relative wide area can be quickly shown.
Following is a short discussion of selected papers on stationary contacts (my personal comments are shown in italic characters):
CONTACT RESISTANCE COMPARISON OF GOOD AND BAD CRIMP JOINTS
WITH TINNED WIRES UNDER THERMAL SHOCK
D. Ron Liu, Tom Bracket and Shaun McCarthy
Ford Motor Company
ABSTRACT
#16 wire gauge crimp joints of good quality were made with tinned wires in the conventional
way. Some of them were then subjected to twisting resulting in a gap between the two wings. All of them were heat-soaked at 135oC for 300 hours. They were then loaded into a thermal shock furnace for thermal cycling from -40oC to 125oC, each cycle lasting one hour for a total of 570 hours. The four-leads method was used to measure the contact resistance for every cycle under the dry circuit condition. The contact resistance of good crimps generally increased at a slower pace over time than the bad ones. The resistance increase of some good and bad crimps would tend to more or less level off after 100-200 cycles while others would continue to increase their resistance without leveling off and some of them might show a sudden jump. Nevertheless, the measured resistance history showed that a crimp with a tinned wire exhibited accepted performance whether it was a good or not so good a crimp. The results also showed that the temperature history would affect the contact resistance measured at a later time. For example, the resistance of a crimp at 125oC would be somehow different depending on whether the previous temperature started from -40oC or from -17oC. Data analysis showed that even with severe thermal shocks for 570 hours and possible consequence of repeated shearing, the contact in the crimp was still essentially a metallic one.
PVD: A pretty limited investigation to confirm the supposed positive effect of tinplating on the wires in automotive crimp applications. They use 20 m as a resistance criterion for crimps! They did not directly compare to unplated copper wires, nor did they investigate thickness and composition of the tin layer. One contact out of 8 was far more stable than the others, two contacts exceeded 3 m after a temperature cycling test, which was the only test performed. Interesting is that they reason that the existence of metallic contact can be derived from the resistance change caused by temperature variation. The construction in this test is such that the wires are subjected to tensile stress at high temperature and to compressive stress at the low temperature.
Break Are Study for the New Electrical Level of 42 V in
Automotive Applications
N.BenJemaa, L.Doublet, L.Morin, D.Jeannot
Universities of Rennes and Tohoku, Metalor and Delphi
ABSTRACT
In order to fulfil the increasing need for electric power in automobiles, to satisfy the new environmental requirements and to decrease the weight of cars, the electrical supply, must be changed from the current 14 V to 42 V. In the present work using 42 V, we have studied are parameters such as break arc duration and extinction gap for different materials, contact opening speeds and circuit loads (correlated with the time constant of the circuit, L/R). We have established that these main arc parameters are greatly enhanced compared to the 14 V are studied in our previous work. In the case of an inductive or a resistive load, it has been found that there are two domains: a low current domain where the material has no significant effect, and a high current domain where some materials (primarily AgSnO2) induce high arc durations and large extinction gap. In addition, increasing the opening speed reduces arc duration in all cases. The increased opening speed can however, increase the extinction gap for inductive loads and decrease it for resistive circuits. We have found that reducing arc duration is always beneficial with regards to erosion but in some cases, however it may increase the extinction gap.
At 42 V, the erosion and the material transfer, from the cathode to the anode, are similar to that obtained at low extinction gaps (1 mm) at 14 V. At large extinction gap, however, these transfer phenomena are considerably modified by a new mechanism that induces the erosion of the cathode and the anode. It has been found that the classification of material behavior versus erosion is completely different at this voltage. For example AgSn02, which is claimed as a best compromise at 14 V for all loads, cannot be used at 42 V for two reasons. It exhibits high erosion and requires a larger contact gap to ensure a successful break.
CONCLUSION
Unfortunately regarding the tested range of materials, no material fulfils the switching duties at 42 V because of poor arc extinction capacity with high inductive loads. That means that in those cases, material developments and/or design modifications are necessary.
Effect of Intergranular Cohesion on the Intermittency of
Automotive Headlamp Switch Contacts
K. Klungtvedt, TRW Automotive and M. Braunovie MB Interface
ABSTRACT
The effect of intergranular cohesion of silver-plating on the intermittent operation of a lubricated sliding automotive headlamp switch was investigated. Fretting types of testing were used to follow the evolution of the intermittent behavior of the switch. It was found that processing variations of the silver electroplate exerted pronounced effect on the quality and surface topography of silver-plated contacts. The intermittency was found to be a switch break-in phenomenon caused by the changes in surface topology resulting from a reduced intergranular cohesion of silver-plating. Subsequent burnishing eliminated the intermittency and was not present later in the switch life. Plausible explanations to account for the observed intermittent effect were discussed. Fretting type of testing proved to be a very useful technique in obtaining the information on the quality of plating that simple hardness measurement could not provide.
CONCLUSIONS
- Fretting tests can be used in lieu of hardness testing for determining and monitoring the quality of silver plating.
- The lack of control of the recommended plating procedures resulted in a loss of the intergranular cohesion of silver plating.
- If fretting is used as a quality control method, wear characteristics can be better characterized and its wide-spread use could, in turn, create a bank of data to further improve knowledge about plating quality and mechanisms of wear.
- This should work well for other materials such as gold. Gold plating baths could be characterized by fretting and porosity tests.
- Friction should be looked at as a variable for further investigation, especially in the initial wear track development.
PVD:Whether fretting tests can be generally used as a quality control method for plating layers, as proposed by the authors, seems highly questionable to me. This work anyhow demonstrates the importance of the plating process for the plating layer properties and shows a surprising application from fretting tests.
Stick and slip definitions are inappropriately used in this paper.
Experimental Study on 3-D Analysis of Contact Surfaces
with a Digital Scanning Laser Microscope
Makoto Hasegawa, Jiro Makimoto and Koichiro Sawa
Chitose Institute and Keio University
ABSTRACT
Theauthors have been interested in a Scanning Laser microscope (SLM) and applied it to studies of contact phenomena. In particular, a digital SLM is being currently used, and confirmed to be a successful tool for investigating the contact phenomena. In this paper, the theory and mechanism of a digital SLM are briefly explained, and some actual data obtained with the digital SLM are presented for demonstrating its usefulness for studies of contact phenomena.
PVD: main advantages Laser Microscopy compared to Electron Microscopy are that vacuum and conductive surfaces are not required and that wide areas can quicker be investigated.
CONSTRICTION RESISTANCE AT HIGH SIGNAL FREQUENCIES
J.D. Lavers and R.S. Timsit
Toronto University and Timron Consultancy
ABSTRACT
Thispaper describes the dependence of constriction resistance on signal frequency. This dependence was calculated for circular constrictions ranging in diameter from 10 to 100 micrometers, and for frequencies ranging from DC to 1 GHz.
The results indicate that the magnitude of constriction resistance does not deviate appreciably from values predicted by Holm's classical analytical expression, as long as the skin depth is large compared with the constriction radius. For skin depths that are much smaller than the constriction radius, constriction resistance decreases with increasing frequency to an apparent limiting value independent of the constriction radius. At high frequencies, constriction resistance constitutes only one of two components of the total connection resistancemeasured in practice. The second component of connection resistance isdetermined by details of the geometry and dimensions of the contact interface, and increases with signal frequency.
PVD: It looks to me that the theory for a signal constriction is not representative for a real contact when it consists of a group of constrictions. The constriction resistances as in this model are in my opinion probably not the dominating factor in high frequency contacts. The author calculated the capacitance and found it to be 60 m at 1 GHz, 6 m at 10 GHz.
High Frequency Considerations for Multi-Point Contact Interfaces
Robert D. Malucci, Consultant
ABSTRACT
A statistical model based on random variations of surface features was used to estimate the resistance and capacitance of a typical multi-point contact interface. Values for clean and degraded contacts were calculated and show, as a contact degrades, the resistance goes up and the capacitance initially rises and then falls as a film grows at the contact interface. Moreover, data were provided that shows consistency with the predictions from the statistical model. In addition, measurements of the skin effect on series resistance, including contact resistance, were conducted and show a power law frequency dependence of both bulk and contact resistance. While these data appear consistent with the analysis, it is believed the measurement and analysis techniques can be improved to provide more accurate results. Moreover, the results reveal that high frequency data transmission can be effected by the impedance of a degraded contact interface. While the latter wasn't fully quantified, this study showed the levels where degradation may impact high frequency signal propagation. It is believed that further refinement of the techniques used in this study, will help quantify high frequency effects from the impedance of a multi-point contact interface.
PVD: In this paper a multi-contact model was modeled for a statistical analysis. Again: the constriction resistances as in this model are in my opinion probably not the dominating factor in high frequency contacts
Effects of Electric Contact Failure on Signal Transmission
in Unmatched Circuits
Baisheng Sun, Beijing University
ABSTRACT
It is found that one of the most important reasons for causing high error code rates in optical
communication systems is the contact failure of the coaxial electrical connectors installed in the systems. The influences of the contact failure on the digital signal transmission in ideal circuits have already been studied theoretically and experimentally. Based on those results, this paper further studies theoretically the effects of contact failure on the digital signal transmission in unmatched circuits, which can happen widely in practical applications. Derivation shows that the effects of contact failure in unmatched circuits on the signal transmission are very complex. Multi-reflection of the signals will occur in the circuit. But one thing is certain that the probability of occurrence of error codes can be increased significantly.
ANALYSES ON THIN FILM BETWEEN CONTACTS BY USING
THIRD HARMONIC DISTORTION
Eisuke Takano, Consultant
ABSTRACT
This paper describes a graphic method to evaluate the effective physical parameters (potential barrier height and film thickness) of a thin insulating film for the tunnel current. The theoretical third harmonic distortion (THD)of the contact current due to the tunnel effect is expressed as a function of the tunnel resistivity and illustrated in a graph, which makes it possible to determine the physical parameters. Experimental results, using Au vs. Au0.5%Co alloy contacts at very small contact loads (1 mN), show that the THDand the contact resistance are very high when the contacts are contaminated with an organic vapor of practical soldering. By making use of the results, the effective potential barrier height for electron emission from the contact metal into the organic film is evaluated at voltages of less than 0.3 eV and thickness of the film at 0.5-0.7 nm. It is possible to estimate the large THD using the volt-tunnel resistance characteristics without measuring the third harmonic. The electric current due to the field emission through the film is theoretically evaluated to be much less than the tunnel current at low voltages applied.
PVD: I believe the that the extremely low normalforce and extremely thin film make application to connector contacts impractical
Lubrication mechanisms of hot-dipped tin
separable electrical contacts
S. Noël, N. Lécaudé, D.Alamarguy, L. Tristani
Université Paris, Supélec, FCI
ABSTRACT
Degradation phenomena occurring during the lifetime of tinned separable electrical contacts remain a factor of loss of reliability that can be minimised. In a previous paper, friction, wear and electrical properties of hot-dipped tin coatings on bronze substrates have been analysed with various techniques in order to show the improvement due to a well-suited fluorinated lubricant layer. Contacts were of the sphere on plane type obtained from strips of tinned CuSn4 (as received for the flats, and formed by stamping for the dimples). Macroscopic friction cycles simulating insertion and withdrawal of separable contacts were performed as well as fretting cycles. Efficiency of the lubricant was strongly related to the filmthickness in the case of macroscopic friction of dimple on flat contacts. For a sufficient film thickness different behaviours were observed for different molecules. Here the particularity of lubrication mechanisms of hot-dipped tin contacts is analysed.
The evolution of static contact resistance values before friction and during the friction tests correlated to the wear behaviour shows the influence of some of the lubricant properties such as viscosity and chain structure.
CONCLUSION
The effect of a low viscosity and low tension energy fluid is to postpone wear and lead to very thin powder like particles. The combination of these two properties seems to be favourable; the next step being to find a proper anti corrosion agent corresponding to tin.
PVD: Conclusions present nothing new or remarkable, the observation of tin and tin oxide in the form of small oxidized tin globules is interesting, it is even stated that the accumulation of powder-like wear oxide debris maintains the contact resistance at a low value!
Photovoltaic Connector Behaviour
under Accelerated Fretting Testing Regimes
AbuBakr Babaj, Patrick James, John McBride
University of Southampton
ABSTRACT
Photovoltaic modules have no moving parts and last upwards of 25 years with no maintenance aside from the occasional cleaning. The installation of modules in building facades and other structures has necessitated the use of push fit connectors to enable quick and easy inter-module dc electrical connection. New applications for photovoltaics such as roof shingles (tiles) place further performance demands on connectors. The day-night variation in temperature within a PV roof for example, creates expansion of components. This paper details the behaviour of a tin plated copper, photovoltaic connector under small amplitude fretting tests (10-100 m) using a specially developed accelerated lifetime test rig. The mated connector creates a high force, multiple point contact between the male and female components by the use of a pre-stressed spring collar. The study shows that a transition amplitude exists (~13 m) above which gross slip at the connector interface appears to occur. This causes a gradual, linear increase in contact resistance, followed by a sudden change to rapid wearing of the tin plating on both the connector surfaces and spring collar, leading to connector failure. Below the transition amplitude, partial slip at the connector interface is observed which creates a stable, low contact resistance. The paper highlights the need to maintain a partial slip/stick condition within a PV connector for long term contact resistance stability. The implication of this requirement to photovoltaic connector design and application is discussed, considering the benefit of flexible connector housings and lubricants in particular.
PVD: another proof that the ELECON theory on fretting is valid.
High Cycle Fretting Corrosion Studies on Tin-Coated Contact Materials
Christopher E. Heaton and Shaun L. MeCarthy, Ford Motor Company
ABSTRACT
The high-cycle (above 20,000) fretting contact characteristics of matte tin-plated copper are reported in this paper. Current loads extended from 0.1 mA to 100mA with an open circuit voltage of 12 Volts. As observed in the past, there is a plateau in the contact resistance versus fretting cycles above 20,000 cycles. Here, we will be reporting on changes in the plateau as a function of load current. Box plots of the median values of the distribution of contact resistances show a dramatic decrease with increasing current. Contact voltages are also seen to range from 1 to 12 Volts depending on the current. These results will be discussed in terms of changes in the granular interface between the contacts with increasing current.