ASTM B920-01
(Practice)Standard Practice for Porosity in Gold and Palladium Alloy Coatings on Metal Substrates by Vapors of Sodium Hypochlorite Solution
Standard Practice for Porosity in Gold and Palladium Alloy Coatings on Metal Substrates by Vapors of Sodium Hypochlorite Solution
SCOPE
1.1 This test practice covers equipment and methods for revealing the porosity of gold and palladium coatings, particularly electrodeposits and clad metals used on electrical contacts.
1.2 This test practice is suitable for coatings containing gold or 75 % by mass of palladium on substrates of copper, nickel, and their alloys, which are commonly used in electrical contacts.
1.3 A variety of full porosity testing methods is described in the literature. These porosity Test Methods are B 735, B 741, B 798, B 799, and B 809. An ASTM Guide to the selection of porosity tests for electrodeposits and related metallic coatings is available as Guide B 765.
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific hazards, see Section 6.
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Designation:B920–01
Standard Practice for
Porosity in Gold and Palladium Alloy Coatings on Metal
Substrates by Vapors of Sodium Hypochlorite Solution
This standard is issued under the fixed designation B 920; 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 B 741 Test Method for Porosity in Gold Coatings on Metal
Substrates by Paper Electrography
1.1 This test practice covers equipment and methods for
B 765 Guide for Selection of Porosity Tests for Electrode-
revealing the porosity of gold and palladium coatings, particu-
posits and Related Metallic Coatings
larly electrodeposits and clad metals used on electrical con-
B 798 Test Method for Porosity in Gold or Palladium
tacts.
Coatings on Metal Substrates by Gel-Bulk Electrography
1.2 This test practice is suitable for coatings containing gold
B 799 Test Method for Porosity in Gold and Palladium
or 75 % by mass of palladium on substrates of copper, nickel,
Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
and their alloys, which are commonly used in electrical
B 809 Test Method for Porosity in Metallic Coatings by
contacts.
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
1.3 Avariety of full porosity testing methods is described in
,
2 3
theliterature. TheseporosityTestMethodsareB 735,B 741,
3. Terminology
B 798, B 799, and B 809. An ASTM Guide to the selection of
3.1 Definitions—Many terms used in this practice are de-
porosity tests for electrodeposits and related metallic coatings
fined in Terminology B 542 and terms relating to metallic
is available as Guide B 765.
coatings are defined in Terminology B 374.
1.4 The values stated in SI units are to be regarded as
3.2 Definitions of Terms Specific to This Standard:
standard. The values given in parentheses are for information
3.2.1 corrosion products—those reaction products emanat-
only.
ingfromtheporesthatprotrudefrom,orareotherwiseattached
1.5 This standard does not purport to address all of the
to, the coating surface after a vapor test exposure.
safety concerns, if any, associated with its use. It is the
3.2.2 metallic coatings—include platings, claddings, or
responsibility of the user of this standard to establish appro-
other metallic layers applied to the substrate. The coatings can
priate safety and health practices and determine the applica-
comprise a single metallic layer or a combination of metallic
bility of regulatory limitations prior to use. For specific
layers.
hazards, see Section 6.
3.2.3 porosity—the presence of any discontinuity, crack, or
2. Referenced Documents hole in the coating that exposes a different underlying metal.
3.2.4 underplate—a metallic coating layer between the
2.1 ASTM Standards:
substrate and the topmost layer or layers. The thickness of an
B 374 Terminology Relating to Electroplating
underplate is usually greater than 0.8 µm (30 µin.).
B 542 Terminology Relating to Electrical Contacts and
Their Use
4. Summary of Practice
B 735 Test Method for Porosity in Gold Coatings on Metal
5 4.1 The test practice employs a solution of sodium hy-
Substrates by Nitric Acid Vapor
pochlorite, a material readily available as household bleach.
The test is recommended primarily as a qualitative means for
This practice is under the jurisdiction ofASTM Committee B02 on Nonferrous assessing the plating quality in electrical connectors and is
Metals and Alloys and is the direct responsibility of Subcommittee B02.11 on
desirable because it uses readily available reagents and equip-
Electrical Contact Test Methods.
mentandisextremelyinexpensive,simple,andfast.Inthetest,
Current edition approved Nov. 10, 2001. Published January 2002.
the coated parts to be evaluated are suspended above a solution
For example see: Nobel, F. J., Ostrow, B. D., and Thompson, D. W., “Porosity
Testing of Gold Deposits,” Plating, Vol 52, 1965, p. 1001.
of sodium hypochorite in a vessel that is closed but not sealed.
S. J. Krumbien, Porosity Testing of Contact Platings, Proceedings, Connectors
Paper towels extend from the solution in the bottom part of the
and Interconnection Technology Symposium, Oct. 1987, p. 47.
4 way up the sides of vessel providing a wicking action for the
Annual Book of ASTM Standards, Vol 02.05.
Annual Book of ASTM Standards, Vol 02.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B920
solution. After exposure in this manner for 30 to 45 min, the reactions with the substrate or underplate. In addition, it can be
parts are removed from the vessel, dried with hot air and used on contacts having complex geometry such as pin-socket
examined for the presence of corrosion products that indicate contacts (although with deep recesses it is preferred that the
porosity. contact structures be opened to permit reaction of the vapors
4.2 For more quantitative characterization of porosity it is with the interior significant surfaces).
better to use one of the previously mentioned porosity test 5.5 Therelationshipofporositylevelsrevealedbyparticular
standards.This practice is oftentimes used as an early predictor teststocontactbehaviormustbemadebytheuserofthesetests
of the likelihood of failure in a full mixed flowing gas (MFG) throughpracticalexperienceorbyotherformsoftesting.Thus,
test used as an accelerated environmental test. absence of porosity in the coating may be a requirement for
4.3 Exposure periods may vary, depending upon the degree some applications, while a few pores in the contact zone may
of porosity to be revealed. Reaction of the gas with a be acceptable for others. The acceptable number, sizes and
corrodable base metal at pore sites produces reaction products locationsoftheporecorrosionproductsshallbeasspecifiedon
that appear as discrete spots on the gold or palladium surface. the appropriate drawing or specification.
Individual spots may be counted with the aid of a loupe or 5.6 This test is considered destructive in that it reveals the
low-power stereomicroscope. presence of porosity by contaminating the surface with corro-
4.4 This porosity test involves corrosion reactions in which sion products and by undercutting the coating at pore sites or
the products delineate defect sites in coatings. Since the at the boundaries of the unplated areas. Any parts exposed to
chemistry and properties of these products may not resemble this test shall not be placed in service.
those found in natural or service environments this test is not 5.7 The test is simple and inexpensive. The cost associated
recommended for prediction of the electrical performance of with the test is very low, using standard basic equipment found
contacts unless correlation is first established with service in an industrial laboratory. There are minimal waste disposal
experience. issues associated with the procedure. The test is very popular
because of its very quick means of assessing the likelihood of
5. Significance and Use
plating quality problems, prior to the performance of acceler-
5.1 Palladium and gold coatings are often specified for the ated environmental testing on the 1-2 week scale at much
contacts of separable electrical connectors and other devices. greater expense.
Electrodeposits are the form of gold that is most used on
6. Safety Hazards
contacts, although it is also employed as inlay or clad metal
6.1 Carry out this test procedure in a clean, working fume
and as weldments on the contact surface. The intrinsic nobility
hood. The vapor emitted is toxic, corrosive, and irritating.
of gold and palladium alloys enables it to resist the formation
6.2 Because the test is conducted in a reaction vessel using
of insulating oxide films that could interfere with reliable
a loose-fitting cover, it is desirable to insure that the drafts
contact operation.
often found in hoods are not so high as to adversely effect the
5.2 In order for these coatings to function as intended,
reproducibility of the test within the reaction vessel.
porosity, cracks, and other defects in the coating that expose
base-metal substrates and underplates must be minimal or 6.3 Observe good laboratory practices when handling the
sodium hypochlorite (household bleach) solution. In particular,
absent, except in those cases where it is feasible to use the
contacts in structures that shield the surface from the environ- wear eye protection completely enclosing the eyes, and make
eye wash facilities readily available.
ment or where corrosion inhibiting surface treatments for the
deposit are employed. The level of porosity in the coating that
7. Apparatus
may be tolerable depends on the severity of the environment to
7.1 Test Glassware, a vessel of sufficient size such that the
the underplate or substrate, design factors for the contact
sodium hypochlorite solution at least 1 cm in depth can be
device like the force with which it is mated, circuit parameters,
placed in the bottom of the vessel without interfering with the
and the reliability of contact operation that it is necessary to
samples. The vessel (see Figs. 1 and 2) shall be made of glass
maintain. Also, when present, the location of pores on the
or plastic not having a gastight lid, such as a glass beaker with
surface is important. If the pores are few in number and are
a watch glass cover or desiccator.
outside of the zone of contact of the mating surfaces, their
7.2 Specimen Holders or Supports, may be made of glass,
presence can often be tolerated.
polytetrafluoroethylene, or other inert materials. It is essential
5.3 Methods for determining pores on a contact surface are
that the specimens be arranged so as not to impede circulation
most suitable if they enable their precise location and numbers
of the gas. Specimens shall not be closer than 12 mm (0.5 in.)
tobedetermined.Contactsurfacesareoftencurvedorirregular
from the wall o
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