ASTM B799-95(2005)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:B799–95(Reapproved2005)
Standard Test Method for
Porosity in Gold and Palladium Coatings by Sulfurous Acid/
Sulfur-Dioxide Vapor
This standard is issued under the fixed designation B 799; 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 542 Terminology Relating to Electrical Contacts and
Their Use
1.1 This test method covers equipment and methods for
B 735 Test Method for Porosity in Gold Coatings on Metal
determining the porosity of gold and palladium coatings,
Substrates by Nitric Acid Vapor
particularly electrodeposits and clad metals used on electrical
B 741 Test Method for Porosity In Gold Coatings on Metal
contacts.
Substrates by Paper Electrography
1.2 This test method is designed to show whether the
B 765 Guide for Selection of Porosity and Gross Defects
porosity level is less or greater than some value which by
Tests for Electrodeposits and Related Metallic Coatings
experience is considered by the user to be acceptable for the
B 798 Test Method for Porosity in Gold or Palladium
intended application.
Coatings on Metal Substrates by Gel-Bulk Electrography
1.3 Avarietyofotherporositytestingmethodsaredescribed
,
2 3
B 809 Test Method for Porosity in Metallic Coatings By
in the literature. Other porosity test methods are B 735,
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
B 741, B 798, and B 809. An ASTM Guide to the selection of
porosity tests for electrodeposits and related metallic coatings
3. Terminology
is available as Guide B 765.
3.1 Definitions—Many terms used in this test method are
1.4 The values stated in SI units are to be regarded as
defined in Terminology B 542 and terms relating to metallic
standard. The values given in parentheses are for information
coatings are defined in Terminology B 374.
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 become familiar
attached to, the coating surface after a vapor test exposure.
with all hazards including those identified in the appropriate
3.2.2 measurement area (or “significant surface”), n—the
Material Safety Data Sheet (MSDS) for this product/material
surface that is examined for the presence of porosity. The
as provided by the manufacturer, to establish appropriate
significant surfaces or measurement areas of the part to be
safety and health practices, and determine the applicability of
tested shall be indicated on the drawing of the part or by
regulatory limitations prior to use. For specific hazards, see
provision of suitably marked samples.
Section 6.
3.2.2.1 Discussion—For specification purposes, the signifi-
2. Referenced Documents cant surfaces or measurement areas are often defined as those
portions of the surface that are essential to the serviceability or
2.1 ASTM Standards:
functionofthepart,suchasitscontactproperties,orwhichcan
B 374 Terminology Relating to Electroplating
be the source of corrosion products or tarnish films that
interfere with the function of the part.
This test method is under the jurisdiction of ASTM Committee B02 on
3.2.3 metallic coatings, n—include platings, claddings, or
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
other metallic layers applied to the substrate. The coatings can
B02.11 on Electrical Contact Test Methods.
comprise a single metallic layer or a combination of metallic
Current edition approved Nov. 1, 2005. Published November 2005. Originally
approved in 1988. Last previous edition approve in 2000 as B 799 – 95 (2000).
layers.
For example see: Nobel, F. J., Ostrow, B. D., and Thompson, D. W., “ Porosity
3.2.4 porosity, n—the presence of any discontinuity, crack,
Testing of Gold Deposits,” Plating, Vol 52, 1965, p. 1001.
3 or hole in the coating that exposes a different underlying metal.
S. J. Krumbien, Porosity Testing of Contact Platings, Proceedings, Connectors
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 ASTM website. Withdrawn.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B799–95 (2005)
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
surface is important. If the pores are few in number and are
4.1 The test method employs concentrated sulfurous acid
outside of the zone of contact of the mating surfaces, their
(H SO ),whichemitssulfurdioxide(SO )gasaccordingtothe
2 3 2
presence can often be tolerated.
equilibrium reaction:
5.4 Methods for determining pores on a contact surface are
H SO 5 SO 1 H O (1)
2 3 2 2
most suitable if they enable their precise location and numbers
The procedure is similar to one first proposed by Lee and
tobedetermined.Contactsurfacesareoftencurvedorirregular
Ternowski.
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
fromprocedurescapableofdetectingallporositytoprocedures
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 Therelationshipofporositylevelsrevealedbyparticular
chemistry and properties of these products may not resemble
teststocontactbehaviormustbemadebytheuserofthesetests
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.
5.7 This test is considered destructive in that it reveals the
5. Significance and Use
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
5.8 This test is intended to be used for quantitative descrip-
weldmentsonthecontactsurface.Theintrinsicnobilityofgold
tions of porosity (such as number of pores per unit area or per
enables it to resist the formation of insulating oxide films that
contact) only on coatings that have a pore density sufficiently
could interfere with reliable contact operation.
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
5.9 For these purposes, the measurement area,or significant
atmosphere that is used does not attack the palladium if the
surface, shall be defined as those portions of the surface that
specified test conditions are followed. In contrast, palladium
are essential to the serviceability or function of the part, such
coatings are attacked by nitric acid (HNO ) and other strong
3 as its contact properties, or which can be the source of
oxidizing agents, so thatTest Method B 735 cannot be used for
corrosion products or tarnish films that interfere with the
determining the porosity in such coatings.
function of the part. The significant surfaces shall be indicated
5.3 In order for these coatings to function as intended,
on the drawings of the parts, or by the provision of suitably
porosity, cracks, and other defects in the coating that expose
marked samples.
base-metal substrates and underplates must be minimal or
6. Safety Hazards
absent, except in those cases where it is feasible to use the
contacts in structures that shield the surface from
...