ASTM B799-95(2009)
(Test Method)Standard Test Method for Porosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
Standard Test Method for Porosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
SIGNIFICANCE AND USE
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 enables it to resist the formation of insulating oxide films that could interfere with reliable contact operation.
Palladium coatings are sometimes specified as alternatives to gold on electrical contacts and similar electrical component surfaces, both as electrodeposits and as inlay or clad metal. This test method is particularly suitable for determining porosity in palladium coatings, since the reactive atmosphere that is used does not attack the palladium if the specified test conditions are followed. In contrast, palladium coatings are attacked by nitric acid (HNO3) and other strong oxidizing agents, so that Test Method B 735 cannot be used for determining the porosity in such coatings.
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 locatio...
SCOPE
1.1 This test method covers equipment and methods for determining the porosity of gold and palladium coatings, particularly electrodeposits and clad metals used on electrical contacts.
1.2 This test method is designed to show whether the porosity level is less or greater than some value which by experience is considered by the user to be acceptable for the intended application.
1.3 A variety of other porosity testing methods are described in the literature. , Other porosity test methods are B 735, B 741, B 798, 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 become familiar with all hazards including those identified in the appropriate Material Safety Data Sheet (MSDS) for this product/material as provided by the manufacturer, 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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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B799 − 95(Reapproved 2009)
Standard Test Method for
Porosity in Gold and Palladium Coatings by Sulfurous Acid/
Sulfur-Dioxide Vapor
This standard is issued under the fixed designation B799; 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 2. Referenced Documents
1.1 This test method covers equipment and methods for 2.1 ASTM Standards:
determining the porosity of gold and palladium coatings, B374Terminology Relating to Electroplating
particularly electrodeposits and clad metals used on electrical B542Terminology Relating to Electrical Contacts andTheir
contacts. Use
B735Test Method for Porosity in Gold Coatings on Metal
1.2 This test method is designed to show whether the
Substrates by Nitric Acid Vapor
porosity level is less or greater than some value which by
B741Test Method for Porosity In Gold Coatings On Metal
experience is considered by the user to be acceptable for the
Substrates By Paper Electrography (Withdrawn 2005)
intended application.
B765GuideforSelectionofPorosityandGrossDefectTests
1.3 Avarietyofotherporositytestingmethodsaredescribed
for Electrodeposits and Related Metallic Coatings
2,3
in the literature. Other porosity test methods are B735,
B798Test Method for Porosity in Gold or Palladium Coat-
B741, B798, and B809. An ASTM Guide to the selection of
ings on Metal Substrates by Gel-Bulk Electrography
porosity tests for electrodeposits and related metallic coatings
B809Test Method for Porosity in Metallic Coatings by
is available as Guide B765.
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
1.4 The values stated in SI units are to be regarded as
3. Terminology
standard. The values given in parentheses are for information
3.1 Definitions—Many terms used in this test method are
only.
defined in Terminology B542 and terms relating to metallic
1.5 This standard does not purport to address all of the
coatings are defined in Terminology B374.
safety concerns, if any, associated with its use. It is the
3.2 Definitions of Terms Specific to This Standard:
responsibility of the user of this standard to become familiar
3.2.1 corrosion products, n—those reaction products ema-
with all hazards including those identified in the appropriate
nating from the pores that protrude from, or are otherwise
Material Safety Data Sheet (MSDS) for this product/material
attached to, the coating surface after a vapor test exposure.
as provided by the manufacturer, to establish appropriate
safety and health practices, and determine the applicability of
3.2.2 measurement area (or “significant surface”) , n—the
regulatory limitations prior to use. For specific hazards, see
surface that is examined for the presence of porosity. The
Section 6.
significant surfaces or measurement areas of the part to be
tested shall be indicated on the drawing of the part or by
provision of suitably marked samples.
This test method is under the jurisdiction of ASTM Committee B02 on
3.2.2.1 Discussion—For specification purposes, the signifi-
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
cant surfaces or measurement areas are often defined as those
B02.11 on Electrical Contact Test Methods.
Current edition approved Oct. 1, 2009. Published October 2009. Originally
approvedin1988.Lastpreviouseditionapprovein2005asB799–95(2005).DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/B0799-95R09. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
For example see: Nobel, F. J., Ostrow, B. D., and Thompson, D. W., “Porosity Standards volume information, refer to the standard’s Document Summary page on
Testing of Gold Deposits,” Plating, Vol 52, 1965, p. 1001. the ASTM website.
3 5
Krumbien, S. J., “Porosity Testing of Contact Platings,” Proceedings, Connec- The last approved version of this historical standard is referenced on
tors and Interconnection Technology Symposium, Oct. 1987, p 47. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B799 − 95 (2009)
portionsofthesurfacethatareessentialtotheserviceabilityor atmosphere that is used does not attack the palladium if the
functionofthepart,suchasitscontactproperties,orwhichcan specified test conditions are followed. In contrast, palladium
be the source of corrosion products or tarnish films that coatings are attacked by nitric acid (HNO ) and other strong
interfere with the function of the part. oxidizing agents, so thatTest Method B735 cannot be used for
determining the porosity in such coatings.
3.2.3 metallic coatings, n—include platings, claddings, or
other metallic layers applied to the substrate. The coatings can
5.3 In order for these coatings to function as intended,
comprise a single metallic layer or a combination of metallic
porosity, cracks, and other defects in the coating that expose
layers.
base-metal substrates and underplates must be minimal or
absent, except in those cases where it is feasible to use the
3.2.4 porosity, n—the presence of any discontinuity, crack,
contacts in structures that shield the surface from the environ-
orholeinthecoatingthatexposesadifferentunderlyingmetal.
ment or where corrosion inhibiting surface treatments for the
3.2.5 underplate, n—a metallic coating layer between the
deposit are employed. The level of porosity in the coating that
substrate and the topmost layer or layers. The thickness of an
maybetolerabledependsontheseverityoftheenvironmentto
underplate is usually greater that 0.8 µm (30 µin.).
the underplate or substrate, design factors for the contact
deviceliketheforcewithwhichitismated,circuitparameters,
4. Summary of Test Method
and the reliability of contact operation that it is necessary to
4.1 The test method employs concentrated sulfurous acid
maintain. Also, when present, the location of pores on the
(H SO ),whichemitssulfurdioxide(SO )gasaccordingtothe
2 3 2
surface is important. If the pores are few in number and are
equilibrium reaction:
outside of the zone of contact of the mating surfaces, their
H SO 5SO 1H O (1)
presence can often be tolerated.
2 3 2 2
The procedure is similar to one first proposed by Lee and 5.4 Methods for determining pores on a contact surface are
Ternowski. most suitable if they enable their precise location and numbers
tobedetermined.Contactsurfacesareoftencurvedorirregular
4.2 Exposure periods may vary, depending upon the degree
in shape, and testing methods should be suitable for them. In
of porosity to be revealed. Reaction of the gas with a
addition, the severity of porosity-determining tests may vary
corrodable base metal at pore sites produces reaction products
fromprocedurescapableofdetectingallporositytoprocedures
that appear as discrete spots on the gold or palladium surface.
that detect only highly porous conditions.
Individual spots are counted with the aid of a loupe or
low-power stereo microscope.
5.5 Thepresenttestmethodiscapableofdetectingvirtually
all porosity or other defects that could participate in corrosion
4.3 This test method is suitable for coatings containing
reactions with the substrate or underplate. The test is rapid,
95% or more of gold or palladium on substrates of copper,
simple,andinexpensive.Inaddition,itcanbeusedoncontacts
nickel, and their alloys which are commonly used in electrical
having complex geometry such as pin-socket contacts (al-
contacts.
though with deep recesses it is preferred that the contact
4.4 This porosity test involves corrosion reactions in which
structures be opened to permit reaction of the sulfur dioxide
the products delineate defect sites in coatings. Since the
with the interior significant surfaces).
chemistry and properties of these products may not resemble
5.6 Therelationshipofporositylevelsrevealedbyparticular
those found in natural or service environments this test is not
teststocontactbehaviormustbemadebytheuserofthesetests
recommended for prediction of the electrical performance of
through practical experience or by judgment. Thus, absence of
contacts unless correlation is first established with service
porosity in the coating may be a requirement for some
experience.
applications, while a few pores in the contact zone may be
5. Significance and Use acceptable for others.
5.1 Gold coatings are often specified for the contacts of 5.7 This test is considered destructive in that it reveals the
separable electrical connectors and other devices. Electrode-
presence of porosity by contaminating the surface with corro-
posits are the form of gold that is most used on contacts,
sion products and by undercutting the coating at pore sites or
although it is also employed as inlay or clad metal and as at the boundaries of the unplated areas. Any parts exposed to
weldmentsonthecontactsurface.Theintrinsicnobilityofgold
this test shall not be placed in service.
enables it to resist the formation of insulating oxide films that
5.8 This test is intended to be used for quantitative descrip-
could interfere with reliable contact operation.
tions of porosity (such as number of pores per unit area or per
5.2 Palladium coatings are sometimes specified as alterna-
contact) only on coatings that have a pore density sufficiently
tives to gold on electrical contacts and similar electrical
low that the corrosion sites are well separated and can be
component surfaces, both as electrodeposits and as inlay or
readily resolved. As a general guideline this can be achieved
clad metal. This test method is particularly suitable for deter-
for pore densities up to about 100/cm . Above this value the
mining porosity in palladium coatings, since the reactive
testsareusefulforthequalitativedetectionandcomparisonsof
porosity.
5.9 Forthesepurposes,the measurement area,or significant
Lee, F. and Ternowski, M., Proceedings Ninth International Conference on
Electrical Contact Phenomena, Chicago, 1978, p. 215. surface, shall be defined as those portions of the surface that
B799 − 95 (2009)
are essential to the
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