ASTM B799-95(2020)
(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
5.1 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.
5.2 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 B735 cannot be used for determining the porosity in such coatings.
5.3 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.
5.4 Methods for determining pores on a contact surface are most suitable if they enable the...
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. 2, 3 Other porosity test methods are B735, B741, B798, 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 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, health, and environmental practices, and determine the applicability of regulatory limitations prior to use. For specific hazards, see Section 6.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B799 − 95 (Reapproved 2020)
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. A number 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, B374 Terminology Relating to Electroplating
particularly electrodeposits and clad metals used on electrical B542 Terminology Relating to Electrical Contacts and Their
contacts. Use
B735 Test 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
B741 Test 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.
B765 Guide for Selection of Porosity and Gross Defect Tests
1.3 A variety of other porosity testing methods are described
for Electrodeposits and Related Metallic Coatings
2,3
in the literature. Other porosity test methods are B735,
B798 Test 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
B809 Test 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
only.
3.1 Definitions—Many terms used in this test method are
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
responsibility of the user of this standard to become familiar
3.2 Definitions of Terms Specific to This Standard:
with all hazards including those identified in the appropriate
3.2.1 corrosion products, n—those reaction products ema-
Material Safety Data Sheet (MSDS) for this product/material
nating from the pores that protrude from, or are otherwise
as provided by the manufacturer, to establish appropriate
attached to, the coating surface after a vapor test exposure.
safety, health, and environmental practices, and determine the
3.2.2 measurement area (or “significant surface”), n—the
applicability of regulatory limitations prior to use. For specific
surface that is examined for the presence of porosity. The
hazards, see Section 6.
significant surfaces or measurement areas of the part to be
1.6 This international standard was developed in accor-
tested shall be indicated on the drawing of the part or by
dance with internationally recognized principles on standard-
provision of suitably marked samples.
ization established in the Decision on Principles for the
3.2.2.1 Discussion—For specification purposes, the signifi-
Development of International Standards, Guides and Recom-
cant surfaces or measurement areas are often defined as those
mendations issued by the World Trade Organization Technical
portions of the surface that are essential to the serviceability or
Barriers to Trade (TBT) Committee.
function of the part, such as its contact properties, or which can
be the source of corrosion products or tarnish films that
This test method is under the jurisdiction of ASTM Committee B02 on
interfere with the function of the part.
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
B02.05 on Precious Metals and Electrical Contact Materials and Test Methods.
Current edition approved April 1, 2020. Published April 2020. Originally
approved in 1988. Last previous edition approve in 2014 as B799 – 95 (2014). DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/B0799-95R20. 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.
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 (2020)
3.2.3 metallic coatings, n—include platings, claddings, or 5.3 In order for these coatings to function as intended,
other metallic layers applied to the substrate. The coatings can porosity, cracks, and other defects in the coating that expose
comprise a single metallic layer or a combination of metallic base-metal substrates and underplates must be minimal or
layers. absent, except in those cases where it is feasible to use the
contacts in structures that shield the surface from the environ-
3.2.4 porosity, n—the presence of any discontinuity, crack,
ment or where corrosion inhibiting surface treatments for the
or hole in the coating that exposes a different underlying metal.
deposit are employed. The level of porosity in the coating that
3.2.5 underplate, n—a metallic coating layer between the
may be tolerable depends on the severity of the environment to
substrate and the topmost layer or layers. The thickness of an
the underplate or substrate, design factors for the contact
underplate is usually greater that 0.8 μm (30 μin.).
device like the force with which it is mated, circuit parameters,
and the reliability of contact operation that it is necessary to
4. Summary of Test Method
maintain. Also, when present, the location of pores on the
4.1 The test method employs concentrated sulfurous acid
surface is important. If the pores are few in number and are
(H SO ), which emits sulfur dioxide (SO ) gas according to the
2 3 2
outside of the zone of contact of the mating surfaces, their
equilibrium reaction:
presence can often be tolerated.
H SO 5 SO 1H O (1)
2 3 2 2
5.4 Methods for determining pores on a contact surface are
The procedure is similar to one first proposed by Lee and most suitable if they enable their precise location and numbers
Ternowski. to be determined. Contact surfaces are often curved or irregular
in shape, and testing methods should be suitable for them. In
4.2 Exposure periods may vary, depending upon the degree
addition, the severity of porosity-determining tests may vary
of porosity to be revealed. Reaction of the gas with a
from procedures capable of detecting all porosity to procedures
corrodable base metal at pore sites produces reaction products
that detect only highly porous conditions.
that appear as discrete spots on the gold or palladium surface.
5.5 The present test method is capable of detecting virtually
Individual spots are counted with the aid of a loupe or
all porosity or other defects that could participate in corrosion
low-power stereo microscope.
reactions with the substrate or underplate. The test is rapid,
4.3 This test method is suitable for coatings containing
simple, and inexpensive. In addition, it can be used on contacts
95 % or more of gold or palladium on substrates of copper,
having complex geometry such as pin-socket contacts (al-
nickel, and their alloys which are commonly used in electrical
though with deep recesses it is preferred that the contact
contacts.
structures be opened to permit reaction of the sulfur dioxide
4.4 This porosity test involves corrosion reactions in which
with the interior significant surfaces).
the products delineate defect sites in coatings. Since the
5.6 The relationship of porosity levels revealed by particular
chemistry and properties of these products may not resemble
tests to contact behavior must be made by the user of these tests
those found in natural or service environments this test is not
through practical experience or by judgment. Thus, absence of
recommended for prediction of the electrical performance of
porosity in the coating may be a requirement for some
contacts unless correlation is first established with service
applications, while a few pores in the contact zone may be
experience.
acceptable for others.
5. Significance and Use
5.7 This test is considered destructive in that it reveals the
presence of porosity by contaminating the surface with corro-
5.1 Gold coatings are often specified for the contacts of
sion products and by undercutting the coating at pore sites or
separable electrical connectors and other devices. Electrode-
at the boundaries of the unplated areas. Any parts exposed to
posits are the form of gold that is most used on contacts,
this test shall not be placed in service.
although it is also employed as inlay or clad metal and as
weldments on the contact surface. The intrinsic nobility of gold
5.8 This test is intended to be used for quantitative descrip-
enables it to resist the formation of insulating oxide films that
tions of porosity (such as number of pores per unit area or per
could interfere with reliable contact operation.
contact) only on coatings that have a pore density sufficiently
low that the corrosion sites are well separated and can be
5.2 Palladium coatings are sometimes specified as alterna-
readily resolved. As a general guideline this can be achieved
tives to gold on electrical contacts and similar electrical
for pore densities up to about 100/cm . Above this value the
component surfaces, both as electrodeposits and as inlay or
tests are useful for the qualitative detection and comparisons of
clad metal. This test method is particularly suitable for deter-
porosity.
mining porosity in palladium coatings, since the reactive
atmosphere that is used does not attack the palladium if the
5.9 For these purposes, the measurement area, or significant
specified test conditions are followed. In contrast, palladium
surface, shall be defined as those portions of the surface that
coatings are attacked by nitric acid (HNO ) and other strong
are essential to the serviceability or function of the part, such
oxidizing agents, so that Test Method B735 cann
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