1、Designation: B 667 97 (Reapproved 2009)Standard 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 of
2、 revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes equipment and techniques formeasuring electrical contact resistance wit
3、h a probe and thepresentation of results.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of th
4、e user of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet (MSDS) for this product/materialas provided by the manufacturer, to establish appropriatesafety and health practices, and determine the applicability ofregulatory limita
5、tions 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 Specific to This Standard:3.2.1 contact resistance, nth
6、e 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 are often called “ asperities” or, morecommonly,
7、 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 absent (see 4.4 for bulk resistance limitation).3
8、.2.2 contact resistance probe, nan apparatus for deter-mining 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. Significance and Use4.1 Electrical contact resistan
9、ce 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 component is used. It is moreconvenient to dete
10、rmine 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 applicable to the device.4.2 Information on con
11、tact 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 mechanical conditions of thecontact, the geome
12、try 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 in such a way thatvalid comparisons of the
13、 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 connections used to introduce the test current into
14、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 generally includes the following:1This practice is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Allo
15、ys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved April 15, 2009. Published April 2009. Originallyapproved in 1980. Last previous edition approved in 2003 as B 667 97 (2003)1.2For referenced ASTM standards, visit the ASTM website, w
16、ww.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 website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.1
17、.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 indigenousvibrations from inadvertently a
18、ltering 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 the best likelihood ofobtaining repr
19、oducible 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 the contact interface.5.2 Additiona
20、l 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 resistance on sliding or wipe when a slide
21、 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 the spring, bending of the cantilev
22、er, 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 thespecimen on the load cell and to advan
23、ce 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 measured after the probe is observed
24、(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 such cases, fine (for example, 50-m di
25、ameter),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 extremelylarge stresses at the tops of small aspe
26、rities. 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-received (uncleaned) test specimens of t
27、he samesurface material as the samples to be measured. If thevibration-induced fluctuations are greater than 10 %, additionalantivibrational measures should be taken.6.4.2 Wipe should not be introduced when contact resis-tance versus load characteristics are being measured, since aslittle as a few m
28、icrometers of lateral movement can drasticallychange the contact resistance of samples having films.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
29、 applied loadshould also be recorded after a fixed dwell time, usually 10 to 30 s.6.5 The power supply 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 for
30、ward and reversevoltages and the results averaged. Measurements taken withlow frequency a-c sources 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 an
31、d have a large radius of curvature to minimize thepossibility that it may damage the specimen surface. 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 gol
32、d rod having a hemispherical end.Such probes have been used extensively to loads of 10 N. Theycan be 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
33、 types are solid gold rivetscoined to a spherical end, with a radius of curvature of 1.6 mm,as 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, materials other than noble metals andshape
34、s 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 of metals similaror identical to metals
35、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,3See Test Methods B 539, Measuring Contact Resistance of Electrical Conn
36、ec-tions (Static Contacts), in the Annual Book of ASTM Standards, Vol 03.04.4Sproles, E. S. and Drozdowicz, M. H., “Development of an Automatic ContactResistance Probe,” Proceedings of the 14th International Conference on ElectricContacts, Paris, June 1988, pp. 195 199.5For example, Antler, M., Aule
37、tta, L. V., and Conley, J., “An Automated ContactResistance Probe,” Review Science Instruments , Vol 34, 1963, p. 1317.6See, for example, Antler, M., “Contact Resistance of Oxidized Metals:Dependence on the Mating Material,” IEEE Trans. on Components, Hybrids, andManufacturing Technology, Vol 10, pp
38、. 420424, 1987.B 667 97 (2009)2clean, smooth surface such as an 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
39、chuck holding the rod, rivet, or ballmay be mounted in a stable 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 illustrat
40、es different 4-wire methods for fasteningcurrent and voltage leads 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
41、 the probe are notused in accordance with 7.3, the tip may have 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 sa
42、mple and introducecontaminations of their own. Other cleaning 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, a
43、n organic solvent will not beadequate for cleaning the probe tip. 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 smoo
44、th noble metalspecimen, such as a freshly abraded solid gold flat, 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 therepe
45、atability, or ability of the probe to give similar contact resistances, byprobing a reference specimen having a thin, compact film. This providesFIG. 1 Arrangement of Current and Voltage Leads to Probe and to Specimen (Typical)B 667 97 (2009)3an excellent check of the integrity of the probe tip and
46、the mechanical andelectrical functioning of the instrument. Some examples of film-coveredreferences are given in Appendix X1. In working with film-coveredstandards to check measurement consistency, it is necessary to determinecontact resistance repeatedly, for example, by probing the standard ten or
47、more times, and to compare the median values and their spread at severalloads.7.5.2 It is good practice to remove contaminants from thesurface of the test specimen prior to testing, unless theexistence of the contaminant(s) is pertinent to the test. Ex-amples of the latter would arise in the measure
48、ment offield-exposed surfaces or in investigations of the contactproperties of lubricant- or inhibitor-covered samples.8. Presentation of Results8.1 Contact resistance values vary at different locations onthe specimen surface, except with uniformly clean, film-freemetals. Therefore, many contact res
49、istance determinationsshould be made at different places on the surface and statisticalmethods used to present the results. It is common practice todescribe contact resistance 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 unif
