1、Designation: B 667 97 (Reapproved 2003)e1Standard Practice forConstruction and Use of a Probe for Measuring ElectricalContact Resistance1This standard is issued under the fixed designation B 667; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEKeywords were added editorially in December 2003.1. Scope1.1 This practice describes equipment and
3、 techniques formeasuring electrical contact resistance with a probe and thepresentation of results.1.2 The values stated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns, if any,
4、 associated with its use. It is theresponsibility of the user of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet for this product/material as pro-vided by the manufacturer, to establish appropriate safety andhealth practices, a
5、nd determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B 542 Terminology Relating to Electrical Contacts andTheir Use3. Terminology3.1 DefinitionsMany terms used in this practice are de-fined in Terminology B 542.3.2 Definitions of Terms Speci
6、fic to This Standard:3.2.1 contact resistancethe resistance to current flowbetween two touching bodies, consisting of constriction resis-tance and film resistance.3.2.1.1 DiscussionConstriction resistance originates inthe fact that mating surfaces touch in most cases at only theirhigh spots, which a
7、re often called “asperities” or, morecommonly, a-spots. The current flow lines are then forced toconstrict as they funnel through these tiny areas. If oxide filmsor other insulating layers interfere with these metal-to-metalcontacts, the contact resistance will be higher than when suchlayers are abs
8、ent (see 4.4 for bulk resistance limitation).3.2.2 contact resistance probean apparatus for determin-ing electrical contact resistance characteristics of a metalsurface. Probe, in this instance, should be distinguished fromthe classical tool whose function it is to touch or move anobject.4. Signific
9、ance and Use4.1 Electrical contact resistance is an important characteris-tic of the contact in certain components, such as connectors,switches, slip rings, and relays. Ordinarily, contact resistance isrequired to be low and stable for proper functioning of manydevices or apparatus in which the comp
10、onent is used. It is moreconvenient to determine contact resistance with a probe than toincorporate the contact material into an actual component forthe purpose of measurement. However, if the probe contactmaterial is different from that employed in the component, theresults obtained may not be appl
11、icable to the device.4.2 Information on contact resistance is useful in materialsdevelopment, in failure analysis studies, in the manufacturingand quality control of contact devices, and in research.4.3 Contact resistance is not a unique single-valued propertyof a material. It is affected by the mec
12、hanical conditions of thecontact, the geometry and roughness of contacting surfaces,surface cleanliness, and contact history, as well as by thematerial properties of hardness and conductivity of bothcontacting members. An objective of this practice is to defineand control many of the known variables
13、 in such a way thatvalid comparisons of the contact properties of materials can bemade.4.4 In some techniques for measuring contact resistance it isnot possible to eliminate bulk resistance, that is, the resistanceof the metal pieces comprising the contact and the resistance ofthe wires and connecti
14、ons used to introduce the test current into1This practice is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved Dec. 9, 2003. Published December 2003. Originall
15、yapproved in 1980. Last previous edition approved in 1997 as B 667 97.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM
16、 website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the samples. In these cases, the measurement is actually of anoverall resistance, which is often confused with contact resis-tance.5. General Description of a Probe5.1 A probe
17、generally includes the following:5.1.1 Fixtures for holding specimens of varied size andshape and for attaching electrical leads to them.5.1.2 A mechanism that applies a measurable load to thespecimen that can be increased, decreased, or held constant.5.1.3 A shock mounted table to prevent any indig
18、enousvibrations from inadvertently altering the conditions at thecontact interface.5.1.4 A reference surface (the probe) that is pressed againstthe specimen and which is normally made of a noble metal.Noble metals such as pure gold are used because they aresubstantially free of oxide films and have
19、the best likelihood ofobtaining reproducible results.5.1.5 A current source with current and voltage measuringinstrumentation for determining contact resistance. Ordinarily,contact resistance is determined at dry circuit conditions3toavoid changes that may occur due to voltage breakdown orheating at
20、 the contact interface.5.2 Additional electrical circuitry may be included to permitrelated measurements to be obtained, such as the voltagebreakdown or the current versus voltage characteristics offilm-covered surfaces.5.3 Probes are also convenient for determining the depen-dence of contact resist
21、ance on sliding or wipe when a slide isincorporated in the specimen holder. This permits the probe tobe moved small measurable distances after loading.6. Design Aspects6.1 The probe is mounted on one end of a pivoted beam, acantilever, or a coil spring. Force is applied by dead weight,compression of
22、 the spring, bending of the cantilever, orelectromagnetically.6.2 Probe holders have been designed so that force may beapplied to the contact and to an electronic load cell which ismounted between the probe contact and a micrometer spindlethat can be advanced. An alternative design is to mount thesp
23、ecimen on the load cell and to advance the probe directlywith the micrometer spindle. Load and contact resistance arethe usual parameters measured and recorded simultaneously.6.3 A probe can be made by mounting a U-shaped free-standing gold wire to the micrometer spindle (see Fig. 1(b).The load is m
24、easured after the probe is observed (preferablyelectrically) to first touch the specimen from a preliminarycalibration (with a load cell) of micrometer advance versusload. In some cases, where very small (to tens of milligrams)forces are used, it may not be necessary to know the loadprecisely. In su
25、ch cases, fine (for example, 50-m diameter),straight, or U-shaped gold or platinum wires can be used as theprobe.6.4 The apparatus must be isolated from vibration to avoiddamaging the surface film that may exist at the interface to beevaluated. The slightest movement can translate into extremelylarg
26、e stresses at the tops of small asperities. Likewise, bounceshould be avoided when touching the probe to the specimen.Vibration may reveal itself as a noisy signal when contactresistance is continuously monitored electronically.6.4.1 For sensitive surfaces, a preliminary run should bemade on as-rece
27、ived (uncleaned) test specimens of the samesurface material as the samples to be measured. If thevibration-induced fluctuations are greater than 10 %, additionalantivibrational measures should be taken.3See ASTM Standard B 539, Measuring Contact Resistance of ElectricalConnections (Static Contacts),
28、 in the Annual Book of ASTM Standards, Vol 03.04.B 667 97 (2003)e126.4.2 Wipe should not be introduced when contact resis-tance versus load characteristics are being measured, since aslittle as a few micrometers of lateral movement can drasticallychange the contact resistance of samples having films
29、.NOTE 1Some variation of contact resistance with time under load hasbeen found to occur for many materials.4It is therefore recommended that,for continuously monitored runs, the resistance at the final applied loadshould also be recorded after a fixed dwell time, usually 10 to 30 s.6.5 The power sup
30、ply shall be capable of delivering apulse-free source under dry circuit conditions. To avoid errorsthat may arise due to contact potentials and thermal EMFs alld-c measurements should be taken with forward and reversevoltages and the results averaged. Measurements taken withlow frequency a-c sources
31、 automatically compensate for thiserror.7. Requirements of the Probe Contact7.1 The probe is normally made with a pure gold surface,although other noble metals can be used. The probe should besmooth and have a large radius of curvature to minimize thepossibility that it may damage the specimen surfa
32、ce. Anexception to this latter recommendation are the wire probesthat are generally designed for low normal loads (6.3).7.1.1 One early probe design5that has seen much use is a3.2-mm diameter solid gold rod having a hemispherical end.Such probes have been used extensively to loads of 10 N. Theycan b
33、e made by machining gold rods to finish dimensions,followed by burnishing with a glass microscope slide or otherhard smooth surface, using care to maintain the radius of theend.7.1.2 Other common probe types are solid gold rivetscoined to a spherical end, with a radius of curvature of 1.6 mm,4Sprole
34、s, E. S., and Drozdowicz, M. H., “Development of an Automatic ContactResistance Probe,” Proceedings of the 14th International Conference on ElectricContacts, Paris, June 1988, pp. 195199.5For example,Antler, M.,Auletta, L. V., and Conley, J., “AnAutomated ContactResistance Probe,” Review Science Ins
35、truments , Vol 34, 1963, p. 1317.FIG. 1 Arrangement of Current and Voltage Leads to Probe and to Specimen (Typical)B 667 97 (2003)e13as well as balls or hemispheres of similar radius of curvature.Pure gold platings have also been used successfully on thesespherical surfaces.7.1.3 In special cases, m
36、aterials other than noble metals andshapes other than spherical may be used. However, contactresistances obtained in these cases will usually be differentfrom those obtained with spherical gold probes, especially ifthe specimen is film-covered.6NOTE 2In certain cases, it is of interest to use probes
37、 of metals similaror identical to metals or platings of the test specimen. Probing with similarmetals is a procedure of particular practical interest.7.2 When rods are used as probes, a newly fixtured probecontact should be loaded and unloaded ten times against a hard,clean, smooth surface such as a
38、n optical flat to obtain anequilibrium shape, an end that is slightly flattened, before usingit to measure contact resistance. The force used should be themaximum that will be employed in subsequent use of theprobe.7.3 Alternatively, the chuck holding the rod, rivet, or ballmay be mounted in a stabl
39、e position 10 to 15 from theperpendicular. By this or similar means, a repositioning step foreach contact resistance measurement will provide a fresh areaon the probe (without preconditioning against the optical flat).7.4 Fig. 1 illustrates different 4-wire methods for fasteningcurrent and voltage l
40、eads to the probe and specimen thatminimize (Fig. 1(a) or eliminate (Fig. 1(b) their bulk resis-tance contributions to the measured value.7.5 Transfer of nonmetallic film from the sample to theprobe may occur. Therefore, if fresh areas on the probe are notused in accordance with 7.3, the tip may hav
41、e to be wiped cleanfrequently, for example, with lens tissue that has been moist-ened with isopropyl alcohol or other appropriate solvent.Pressurized propellents, such as fluorocarbons or propane,should be avoided as they may chill the sample and introducecontaminations of their own. Other cleaning
42、techniques canalso be used.47.5.1 Metallic transfer to the gold probe surface has beenobserved when soft metals, such as tin and tin-lead alloys, areexamined. This occurrence may affect the results of subsequentprobings. In these cases, an organic solvent will not beadequate for cleaning the probe t
43、ip. Other cleaning proceduresare required, or else the probe tip should be renewed or theprobe area changed, if possible.NOTE 3With the solid gold rod probe, cleanliness is verified bydetermining the contact resistance of a reference smooth noble metalspecimen, such as a freshly abraded solid gold f
44、lat, and comparing thecontact resistance with known values of resistance. These determinationsare best made at smaller loads than are used in the measurements of thematerials themselves. It is a good practice to periodically check therepeatability, or ability of the probe to give similar contact res
45、istances, byprobing a reference specimen having a thin, compact film. This providesan excellent check of the integrity of the probe tip and the mechanical andelectrical functioning of the instrument. Some examples of film-coveredreferences are given in X1. In working with film-covered standards toch
46、eck measurement consistency, it is necessary to determine contactresistance repeatedly, for example, by probing the standard ten or moretimes, and to compare the median values and their spread at several loads.7.5.2 It is good practice to remove contaminants from thesurface of the test specimen prio
47、r to testing, unless theexistence of the contaminant(s) is pertinent to the test. Ex-amples of the latter would arise in the measurement offield-exposed surfaces or in investigations of the contactproperties of lubricant- or inhibitor-covered samples.8. Presentation of Results8.1 Contact resistance
48、values vary at different locations onthe specimen surface, except with uniformly clean, film-freemetals. Therefore, many contact resistance determinationsshould be made at different places on the surface and statisticalmethods used to present the results. It is common practice todescribe contact res
49、istance by any of the following methods:8.1.1 Contact Resistance-Load Characteristic Curves Plot-ted on Logarithmic Coordinates with Medians and ExtremeValues or Standard Deviations Indicated at Various LoadsEach point on such a curve should represent at least sixmeasurements, although ten or more determinations are pre-ferred. This method is especially useful for clean metals ormetals having a uniform insulating film.8.1.2 Frequency of Failure Versus Load, that is, the percentof measurements at given loads which exceed a definedresistance criterion. This method is
