ASTM B667-97

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: B 667 – 97
Standard Practice for
Construction and Use of a Probe for Measuring Electrical
Contact Resistance
This standard is issued under the fixed designation B 667; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope the classical tool whose function it is to touch or move an
object.
1.1 This practice describes equipment and techniques for
measuring electrical contact resistance with a probe and the
4. Significance and Use
presentation of results.
4.1 Electrical contact resistance is an important characteris-
1.2 The values stated in SI units are to be regarded as
tic of the contact in certain components, such as connectors,
standard. The values given in parentheses are for information
switches, slip rings, and relays. Ordinarily, contact resistance is
only.
required to be low and stable for proper functioning of many
1.3 This standard does not purport to address all of the
devices or apparatus in which the component is used. It is more
safety concerns, if any, associated with its use. It is the
convenient to determine contact resistance with a probe than to
responsibility of the user of this standard to establish appro-
incorporate the contact material into an actual component for
priate safety and health practices and determine the applica-
the purpose of measurement. However, if the probe contact
bility of regulatory limitations prior to use.
material is different from that employed in the component, the
2. Referenced Documents results obtained may not be applicable to the device.
4.2 Information on contact resistance is useful in materials
2.1 ASTM Standards:
development, in failure analysis studies, in the manufacturing
B 542 Terminology Relating to Electrical Contacts and
and quality control of contact devices, and in research.
Their Use
4.3 Contact resistance is not a unique single-valued property
3. Terminology
of a material. It is affected by the mechanical conditions of the
contact, the geometry and roughness of contacting surfaces,
3.1 Definitions—Many terms used in this practice are de-
surface cleanliness, and contact history, as well as by the
fined in Terminology B 542.
material properties of hardness and conductivity of both
3.2 Definitions of Terms Specific to This Standard:
contacting members. An objective of this practice is to define
3.2.1 contact resistance—the resistance to current flow
and control many of the known variables in such a way that
between two touching bodies, consisting of constriction resis-
valid comparisons of the contact properties of materials can be
tance and film resistance.
made.
3.2.2 Discussion—Constriction resistance originates in the
4.4 In some techniques for measuring contact resistance it is
fact that mating surfaces touch in most cases at only their high
not possible to eliminate bulk resistance, that is, the resistance
spots, which are often called “asperities” or, more commonly,
of the metal pieces comprising the contact and the resistance of
a-spots. The current flow lines are then forced to constrict as
the wires and connections used to introduce the test current into
they funnel through these tiny areas. If oxide films or other
the samples. In these cases, the measurement is actually of an
insulating layers interfere with these metal-to-metal contacts,
overall resistance, which is often confused with contact resis-
the contact resistance will be higher than when such layers are
tance.
absent (see 4.4 for bulk resistance limitation).
3.2.3 contact resistance probe—an apparatus for determin-
5. General Description of a Probe
ing electrical contact resistance characteristics of a metal
5.1 A probe generally includes the following:
surface. Probe, in this instance, should be distinguished from
5.1.1 Fixtures for holding specimens of varied size and
shape and for attaching electrical leads to them.
This practice is under the jurisdiction of ASTM Committee B-2 on Nonferrous
5.1.2 A mechanism that applies a measurable load to the
Metals and Alloys and is the direct responsibility of Subcommittee B02.11 on
specimen that can be increased, decreased, or held constant.
Electrical Contact Test Methods.
Current edition approved Dec. 10, 1997. Published October 1998. Originally
5.1.3 A shock mounted table to prevent any indigenous
published as B 667 – 80. Last previous edition B 667 – 92.
Annual Book of ASTM Standards, Vol 03.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
B 667
vibrations from inadvertently altering the conditions at the breakdown or the current versus voltage characteristics of
contact interface. film-covered surfaces.
5.1.4 A reference surface (the probe) that is pressed against 5.3 Probes are also convenient for determining the depen-
the specimen and which is normally made of a noble metal. dence of contact resistance on sliding or wipe when a slide is
Noble metals such as pure gold are used because they are incorporated in the specimen holder. This permits the probe to
FIG. 1 Arrangement of Current and Voltage Leads to Probe and to Specimen (Typical)
substantially free of oxide films and have the best likelihood of be moved small measurable distances after loading.
obtaining reproducible results.
6. Design Aspects
5.1.5 A current source with current and voltage measuring
6.1 The probe is mounted on one end of a pivoted beam, a
instrumentation for determining contact resistance. Ordinarily,
cantilever, or a coil spring. Force is applied by dead weight,
contact resistance is determined at dry circuit conditions to
compression of the spring, bending of the cantilever, or
avoid changes that may occur due to voltage breakdown or
electromagnetically.
heating at the contact interface.
6.2 Probe holders have been designed so that force may be
5.2 Additional electrical circuitry may be included to permit
applied to the contact and to an electronic load cell which is
related measurements to be obtained, such as the voltage
mounted between the probe contact and a micrometer spindle
that can be advanced. An alternative design is to mount the
3 specimen on the load cell and to advance the probe directly
See ASTM Standard B 539, Measuring Contact Resistance of Electrical
Connections (Static Contacts), in the Annual Book of ASTM Standards, Vol 03.04.
with the micrometer spindle. Load and contact resistance are
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
B 667
the usual parameters measured and recorded simultaneously. 7.1.2 Other common probe types are solid gold rivets
6.3 A probe can be made by mounting a U-shaped free- coined to a spherical end, with a radius of curvature of 1.6 mm,
standing gold wire to the micrometer spindle (see Fig. 1(b)). as well as balls or hemispheres of similar radius of curvature.
The load is measured after the probe is observed (preferably Pure gold platings have also been used successfully on these
electrically) to first touch the specimen from a preliminary spherical surfaces.
calibration (with a load cell) of micrometer advance versus 7.1.3 In special cases, materials other than noble metals and
load. In some cases, where very small (to tens of milligrams) shapes other than spherical may be used. However, contact
forces are used, it may not be necessary to know the load resistances obtained in these cases will usually be different
precisely. In such cases, fine (for example, 50-μm diameter), from those obtained with spherical gold probes, especially if
straight, or U-shaped gold or platinum wires can be used as the the specimen is film-covered.
probe.
NOTE 2—In certain cases, it is of interest to use probes of metals similar
6.4 The apparatus must be isolated from vibration to avoid
or identical to metals or platings of the test specimen. Probing with similar
damaging the surface film that may exist at the interface to be
metals is a procedure of particular practical interest.
evaluated. The slightest movement can translate into extremely
7.2 When rods are used as probes, a newly fixtured probe
large stresses at the tops of small asperities. Likewise, bounce
contact should be loaded and unloaded ten times against a hard,
should be avoided when touching the probe to the specimen.
clean, smooth surface such as an optical flat to obtain an
Vibration may reveal itself as a noisy signal when contact
equilibrium shape, an end that is slightly flattened, before using
resistance is continuously monitored electronically.
it to measure contact resistance. The force used should be the
6.4.1 For sensitive surfaces, a preliminary run should be
maximum that will be employed in subsequent use of the
made on as-received (uncleaned) test specimens of the same
probe.
surface material as the samples to be measured. If the
7.3 Alternatively, the chuck holding the rod, rivet, or ball
vibration-induced fluctuations are greater than 10 %, additional
may be mounted in a stable position 10 to 15° from the
antivibrational measures should be taken.
perpendicular. By this or similar means, a repositioning step for
6.4.2 Wipe sh
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