ASTM B920-01(2006)e1
(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.
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(Reapproved2006)
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 B920; 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 (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Footnote 6 was removed editorially in September 2007.
1. Scope B735 Test Method for Porosity in Gold Coatings on Metal
Substrates by Nitric Acid Vapor
1.1 This test practice covers equipment and methods for
B741 Test Method for Porosity In Gold Coatings On Metal
revealing the porosity of gold and palladium coatings, particu-
Substrates By Paper Electrography
larly electrodeposits and clad metals used on electrical con-
B765 Guide for Selection of Porosity and Gross Defect
tacts.
Tests for Electrodeposits and Related Metallic Coatings
1.2 Thistestpracticeissuitableforcoatingscontaininggold
B798 Test Method for Porosity in Gold or Palladium
or 75 % by mass of palladium on substrates of copper, nickel,
Coatings on Metal Substrates by Gel-Bulk Electrography
and their alloys, which are commonly used in electrical
B799 Test Method for Porosity in Gold and Palladium
contacts.
Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
1.3 Avariety of full porosity testing methods is described in
,
2 3
B809 Test Method for Porosity in Metallic Coatings by
the literature. These porosity Test Methods are B735, B741,
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
B798, B799, and B809. An ASTM Guide to the selection of
porosity tests for electrodeposits and related metallic coatings
3. Terminology
is available as Guide B765.
3.1 Definitions—Many terms used in this practice are de-
1.4 The values stated in SI units are to be regarded as
fined in Terminology B542 and terms relating to metallic
standard. The values given in parentheses are for information
coatings are defined in Terminology B374.
only.
3.2 Definitions of Terms Specific to This Standard:
1.5 This standard does not purport to address all of the
3.2.1 corrosion products, n—those reaction products ema-
safety concerns, if any, associated with its use. It is the
nating from the pores that protrude from, or are otherwise
responsibility of the user of this standard to establish appro-
attached to, the coating surface after a vapor test exposure.
priate safety and health practices and determine the applica-
3.2.2 metallic coatings, n—include platings, claddings, or
bility of regulatory limitations prior to use. For specific
other metallic layers applied to the substrate. The coatings can
hazards, see Section 6.
comprise a single metallic layer or a combination of metallic
2. Referenced Documents layers.
4 3.2.3 porosity, n—the presence of any discontinuity, crack,
2.1 ASTM Standards:
or hole in the coating that exposes a different underlying metal.
B374 Terminology Relating to Electroplating
3.2.4 underplate, n—a metallic coating layer between the
B542 Terminology Relating to Electrical Contacts and
substrate and the topmost layer or layers. The thickness of an
Their Use
underplate is usually greater than 0.8 µm (30 µin.).
This practice is under the jurisdiction ofASTM Committee B02 on Nonferrous 4. Summary of Practice
Metals and Alloys and is the direct responsibility of Subcommittee B02.11 on
4.1 The test practice employs a solution of sodium hy-
Electrical Contact Test Methods.
Current edition approved Dec. 1, 2006. Published December 2006. Originally pochlorite, a material readily available as household bleach.
approved in 2001. Last previous edition approved in 2001 as B920 - 01. DOI:
The test is recommended primarily as a qualitative means for
10.1520/B0920-01R06E01.
assessing the plating quality in electrical connectors and is
For example see: Nobel, F. J., Ostrow, B. D., and Thompson, D. W., “Porosity
desirable because it uses readily available reagents and equip-
Testing of Gold Deposits,” Plating, Vol 52, 1965, p. 1001.
S. J. Krumbien, Porosity Testing of Contact Platings, Proceedings, Connectors
mentandisextremelyinexpensive,simple,andfast.Inthetest,
and Interconnection Technology Symposium, Oct. 1987, p. 47.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Withdrawn. The last approved version of this historical standard is referenced
the ASTM website. on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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B920–01 (2006)
the coated parts to be evaluated are suspended above a solution 5.4 Thepresenttestpracticeiscapableofdetectingvirtually
of sodium hypochorite in a vessel that is closed but not sealed. all porosity or other defects that could participate in corrosion
Paper towels extend from the solution in the bottom part of the reactions with the substrate or underplate. In addition, it can be
way up the sides of vessel providing a wicking action for the used on contacts having complex geometry such as pin-socket
solution. After exposure in this manner for 30 to 45 min, the contacts (although with deep recesses it is preferred that the
parts are removed from the vessel, dried with hot air and contact structures be opened to permit reaction of the vapors
examined for the presence of corrosion products that indicate with the interior significant surfaces).
porosity. 5.5 Therelationshipofporositylevelsrevealedbyparticular
teststocontactbehaviormustbemadebytheuserofthesetests
4.2 For more quantitative characterization of porosity it is
throughpracticalexperienceorbyotherformsoftesting.Thus,
better to use one of the previously mentioned porosity test
absence of porosity in the coating may be a requirement for
standards.Thispractice is oftentimes used as an earlypredictor
some applications, while a few pores in the contact zone may
of the likelihood of failure in a full mixed flowing gas (MFG)
be acceptable for others. The acceptable number, sizes and
test used as an accelerated environmental test.
locationsoftheporecorrosionproductsshallbeasspecifiedon
4.3 Exposure periods may vary, depending upon the degree
the appropriate drawing or specification.
of porosity to be revealed. Reaction of the gas with a
5.6 This test is considered destructive in that it reveals the
corrodable base metal at pore sites produces reaction products
presence of porosity by contaminating the surface with corro-
that appear as discrete spots on the gold or palladium surface.
sion products and by undercutting the coating at pore sites or
Individual spots may be counted with the aid of a loupe or
at the boundaries of the unplated areas. Any parts exposed to
low-power stereomicroscope.
this test shall not be placed in service.
4.4 This porosity test involves corrosion reactions in which
5.7 The test is simple and inexpensive. The cost associated
the products delineate defect sites in coatings. Since the
with the test is very low, using standard basic equipment found
chemistry and properties of these products may not resemble
in an industrial laboratory. There are minimal waste disposal
those found in natural or service environments this test is not
issues associated with the procedure. The test is very popular
recommended for prediction of the electrical performance of
because of its very quick means of assessing the likelihood of
contacts unless correlation is first established with service
plating quality problems, prior to the performance of acceler-
experience.
ated environmental testing on the 1 to 2 week scale at much
greater expense.
5. Significance and Use
5.1 Palladium and gold coatings are often specified for the 6. Safety Hazards
contacts of separable electrical connectors and other devices.
6.1 Carry out this test procedure in a clean, working fume
Electrodeposits are the form of gold that is most used on
hood. The vapor emitted is toxic, corrosive, and irritating.
contacts, although it is also employed as inlay or clad metal
6.2 Because the test is conducted in a reaction vessel using
and as weldments on the contact surface. The intrinsic nobility
a loose-fitting cover, it is desirable to insure that the drafts
of gold and palladium alloys enables it to resist the formation
often found in hoods are not so high as to adversely effect the
of insulating oxide films that could interfere with reliable
reproducibility of the test within the reaction vessel.
contact operation.
6.3 Observe good laboratory practices when handling the
5.2 In order for these coatings to function as intended,
sodium hypochlorite (household bleach) solution. In particular,
porosity, cracks, and other defects in the coating that expose
wear eye protection completely enclosing the eyes, and make
base-metal substrates and underplates must be minimal or
eye wash facilities readily available.
absent, except in those cases where it is feasible to use the
7. Apparatus
contacts in structures that shield the surface from the environ-
ment or where corrosion inhibiting surface treatments for the
7.1 Test Glassware, a vessel of sufficient size such that the
deposit are employed. The level of porosity in the coating that
sodium hypochlorite solution at least 1 cm in depth can be
may be tolerable depends on the severity of the environment to
placed in the bottom of the vessel without interfering with the
the underplate or substrate, design factors for the contact
samples. The vessel (see Figs. 1 and 2) shall be made of glass
device like the force with which it is mated, circuit parameters,
or plastic not having a gastight lid, such as a glass beaker with
and the reliability of contact operation that it is necessary to
a watch glass cover or desiccator.
maintain. Also, when present, the location of pores on the
7.2 Specimen Holders or Supports, may be made of glass,
surface is important. If the pores are few in number and are
polytetrafluoroethylene, or other inert materials. It is essential
outside of the zone of con
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