ASTM B920-01(2011)
(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
SIGNIFICANCE AND USE
Palladium and gold coatings are often specified for the contacts of separable electrical connectors and other devices. Electrodeposits are the form of gold that is most used on contacts, although it is also employed as inlay or clad metal and as weldments on the contact surface. The intrinsic nobility of gold and palladium alloys enables it to resist the formation of insulating oxide films that could interfere with reliable contact operation.
In order for these coatings to function as intended, porosity, cracks, and other defects in the coating that expose base-metal substrates and underplates must be minimal or absent, except in those cases where it is feasible to use the contacts in structures that shield the surface from the environment or where corrosion inhibiting surface treatments for the deposit are employed. The level of porosity in the coating that may be tolerable depends on the severity of the environment to the underplate or substrate, design factors for the contact device like the force with which it is mated, circuit parameters, and the reliability of contact operation that it is necessary to maintain. Also, when present, the location of pores on the surface is important. If the pores are few in number and are outside of the zone of contact of the mating surfaces, their presence can often be tolerated.
Methods for determining pores on a contact surface are most suitable if they enable their precise location and numbers to be determined. Contact surfaces are often curved or irregular in shape, and testing methods should be suitable for them. In addition, the severity of porosity-determining tests may vary from procedures capable of detecting all porosity to procedures that detect only highly porous conditions.
The present test practice is capable of detecting virtually all porosity or other defects that could participate in corrosion reactions with the substrate or underplate. In addition, it can be used on contacts having complex geometry such a...
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 B735, B741, B798, B799, and B809. An ASTM Guide to the selection of porosity tests for electrodeposits and related metallic coatings is available as Guide B765.
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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: B920 − 01(Reapproved 2011)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope B735Test Method for Porosity in Gold Coatings on Metal
Substrates by Nitric Acid Vapor
1.1 This test practice covers equipment and methods for
B741Test Method for Porosity In Gold Coatings On Metal
revealing the porosity of gold and palladium coatings, particu-
Substrates By Paper Electrography (Withdrawn 2005)
larly electrodeposits and clad metals used on electrical con-
B765GuideforSelectionofPorosityandGrossDefectTests
tacts.
for Electrodeposits and Related Metallic Coatings
1.2 Thistestpracticeissuitableforcoatingscontaininggold
B798Test Method for Porosity in Gold or Palladium Coat-
or 75% by mass of palladium on substrates of copper, nickel,
ings on Metal Substrates by Gel-Bulk Electrography
and their alloys, which are commonly used in electrical
B799Test Method for Porosity in Gold and Palladium
contacts.
Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
1.3 Avarietyoffullporositytestingmethodsisdescribedin B809Test Method for Porosity in Metallic Coatings by
2,3
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
the literature. These porosity Test Methods are B735, B741,
B798, B799, and B809. An ASTM Guide to the selection of
3. Terminology
porosity tests for electrodeposits and related metallic coatings
is available as Guide B765.
3.1 Definitions—Many terms used in this practice are de-
fined in Terminology B542 and terms relating to metallic
1.4 The values stated in SI units are to be regarded as
coatings are defined in Terminology B374.
standard. The values given in parentheses are for information
only.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 corrosion products, n—those reaction products ema-
1.5 This standard does not purport to address all of the
nating from the pores that protrude from, or are otherwise
safety concerns, if any, associated with its use. It is the
attached to, the coating surface after a vapor test exposure.
responsibility of the user of this standard to establish appro-
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
layers.
2. Referenced Documents
3.2.3 porosity, n—the presence of any discontinuity, crack,
2.1 ASTM Standards:
orholeinthecoatingthatexposesadifferentunderlyingmetal.
B374Terminology Relating to Electroplating
3.2.4 underplate, n—a metallic coating layer between the
B542Terminology Relating to Electrical Contacts andTheir
substrate and the topmost layer or layers. The thickness of an
Use
underplate is usually greater than 0.8 µm (30 µin.).
ThispracticeisunderthejurisdictionofASTMCommitteeB02onNonferrous
4. Summary of Practice
Metals and Alloys and is the direct responsibility of Subcommittee B02.11 on
Electrical Contact Test Methods.
4.1 The test practice employs a solution of sodium
Current edition approved Oct. 1, 2011. Published October 2011. Originally
hypochlorite, a material readily available as household bleach.
ε1
approved in 2001. Last previous edition approved in 2006 as B920–01(2006) .
The test is recommended primarily as a qualitative means for
DOI: 10.1520/B0920-01R011.
For example see: Nobel, F. J., Ostrow, B. D., and Thompson, D. W., “Porosity assessing the plating quality in electrical connectors and is
Testing of Gold Deposits,” Plating, Vol 52, 1965, p. 1001.
desirable because it uses readily available reagents and equip-
Krumbien, S J., 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 The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B920 − 01 (2011)
thecoatedpartstobeevaluatedaresuspendedaboveasolution fromprocedurescapableofdetectingallporositytoprocedures
of sodium hypochorite in a vessel that is closed but not sealed. that detect only highly porous conditions.
Papertowelsextendfromthesolutioninthebottompartofthe
5.4 Thepresenttestpracticeiscapableofdetectingvirtually
way up the sides of vessel providing a wicking action for the
all porosity or other defects that could participate in corrosion
solution. After exposure in this manner for 30 to 45 min, the
reactionswiththesubstrateorunderplate.Inaddition,itcanbe
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.Thispracticeisoftentimesusedasanearlypredictor
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
some applications, while a few pores in the contact zone may
4.3 Exposure periods may vary, depending upon the degree
be acceptable for others. The acceptable number, sizes and
of porosity to be revealed. Reaction of the gas with a
locationsoftheporecorrosionproductsshallbeasspecifiedon
corrodable base metal at pore sites produces reaction products
the appropriate drawing or specification.
that appear as discrete spots on the gold or palladium surface.
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-
sion products and by undercutting the coating at pore sites or
4.4 This porosity test involves corrosion reactions in which
at the boundaries of the unplated areas. Any parts exposed to
the products delineate defect sites in coatings. Since the
this test shall not be placed in service.
chemistry and properties of these products may not resemble
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
withthetestisverylow,usingstandardbasicequipmentfound
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-
ated environmental testing on the 1 to 2 week scale at much
5.1 Palladium and gold coatings are often specified for the
greater expense.
contacts of separable electrical connectors and other devices.
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
and as weldments on the contact surface.The intrinsic nobility
6.1 Carry out this test procedure in a clean, working fume
of gold and palladium alloys enables it to resist the formation
hood. The vapor emitted is toxic, corrosive, and irritating.
of insulating oxide films that could interfere with reliable
6.2 Because the test is conducted in a reaction vessel using
contact operation.
a loose-fitting cover, it is desirable to insure that the drafts
5.2 In order for these coatings to function as intended,
often found in hoods are not so high as to adversely effect the
porosity, cracks, and other defects in the coating that expose
reproducibility of the test within the reaction vessel.
base-metal substrates and underplates must be minimal or
6.3 Observe good laboratory practices when handling the
absent, except in those cases where it is feasible to use the
sodiumhypochlorite(householdbleach)solution.Inparticular,
contacts in structures that shield the surface from the environ-
wear eye protection completely enclosing the eyes, and make
ment or where corrosion inhibiting surface treatments for the
eye wash facilities readily available.
deposit are employed. The level of porosity in the coating that
maybetolerabledependsontheseverityoftheenvironmentto
7. Apparatus
the underplate or substrate, design factors for the contact
deviceliketheforcewithwhichitismated,circuitparameters, 7.1 Test Glassware, a vessel of sufficient size such that the
and the reliability of contact operation that it is necessary to
sodium hypochlorite solution at least 1 cm in depth can be
maintain. Also, when present, the location of pores on the placed in the bottom of the vessel without interfering with the
surface is important. If the pores are few in number and are
samples. The vessel (see Figs. 1 and 2) shall be made of glass
outside of the zone of contact of the mating surfaces, their or plastic not having a gastight lid, such as a glass beaker with
presence can often be tolerated.
a watch glass cover or desiccator.
5.3 Methods for determining pores
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.