1、Designation: B667 97 (Reapproved 2014)Standard Practice forConstruction and Use of a Probe for Measuring ElectricalContact Resistance1This standard is issued under the fixed designation B667; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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 with
3、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 the
4、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 limitati
5、ons prior to use.2. Referenced Documents2.1 ASTM Standards:2B542 Terminology Relating to Electrical Contacts and TheirUse3. Terminology3.1 DefinitionsMany terms used in this practice are de-fined in Terminology B542.3.2 Definitions of Terms Specific to This Standard:3.2.1 contact resistance, nthe re
6、sistance to current flowbetween two touching bodies, consisting of constriction resis-tance and film resistance.3.2.1.1 DiscussionConstriction resistance originates in thefact that mating surfaces touch in most cases at only their highspots, which are often called “asperities” or, more commonly,a-sp
7、ots. The current flow lines are then forced to constrict asthey funnel through these tiny areas. If oxide films or otherinsulating layers interfere with these metal-to-metal contacts,the contact resistance will be higher than when such layers areabsent (see 4.4 for bulk resistance limitation).3.2.2
8、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 resistance is
9、 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 determine
10、 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 contact
11、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 geometry a
12、nd 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 cont
13、act 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 intothe s
14、amples. In these cases, the measurement is actually of anoverall resistance, which is often confused with contact resis-tance.1This practice is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Tes
15、t Methods.Current edition approved Oct. 1, 2014. Published October 2014. Originallyapproved in 1980. Last previous edition approved in 2009 as B667 97 (2009).DOI: 10.1520/B0667-97R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.
16、org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. General Description of a Probe5.1 A probe generally includes
17、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 indigenousvibrations fro
18、m 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 the best likelihood
19、 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 the contact interf
20、ace.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 resistance on sliding or
21、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 the spring, bendin
22、g 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 thespecimen on the load
23、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 measured after the p
24、robe 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 such cases, fine (for
25、 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 extremelylarge stresses at the t
26、ops 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-received (uncleaned) te
27、st specimens of the 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 as
28、little as a few micrometers 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 resist
29、ance at the final 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
30、be taken with forward 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 s
31、hould besmooth and 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 d
32、iameter solid gold 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 O
33、ther common probe 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 nobl
34、e 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 of metals similar3See T
35、est Methods B539, Measuring Contact Resistance of Electrical Connec-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 ElectricConta
36、cts, Paris, June 1988, pp. 195199.5For example, Antler, M.,Auletta, L. V., and Conley, J., “AnAutomated 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. o
37、n Components, Hybrids, andManufacturing Technology, Vol 10, pp. 420424, 1987.B667 97 (2014)2or 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 lo
38、aded and unloaded ten times against a hard,clean, 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 Alterna
39、tively, the 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.
40、 1 illustrates 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 fr
41、esh areas on 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
42、chill the sample 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 th
43、ese cases, an 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 re
44、ference smooth noble metalFIG. 1 Arrangement of Current and Voltage Leads to Probe and to Specimen (Typical)B667 97 (2014)3specimen, 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
45、 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 resistances, byprobing a reference specimen having a thin, compact film. This providesan excellent check of the integrity of the pro
46、be tip and 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 stan
47、dard ten ormore 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
48、the measurement 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
49、contact resistance 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 hav
