ASTM B866-95

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Designation: B 866 – 95
Standard Test Method for
Gross Defects and Mechanical Damage in Metallic Coatings
by Polysulfide Immersion
This standard is issued under the fixed designation B 866; 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 545 Specification for Electrodeposited Coatings of Tin
detecting gross defects and mechanical damage (including
B 605 Specification for Electrodeposited Coatings of Tin-
wear-through) in metallic coatings where the breaks in the
Nickel Alloy
coating penetrate down to a copper or copper alloy substrate.
B 679 Specification for Electrodeposited Coatings of Palla-
1.2 This test method is suitable for coatings consisting of
dium for Engineering Use
single or combined layers of any coating that does not
B 689 Specification for Electrodeposited Engineering
significantly tarnish in an alkaline polysulfide solution. Ex-
Nickel Coatings
amples are gold, nickel, tin, tin-lead, and palladium, or their
B 733 Specification for Autocatalytic Nickel-Phosphorus
alloys.
Coatings on Metals
1.3 Recent reviews of porosity testing (which include those
B 735 Test Method for Porosity in Gold Coatings on Metal
for gross defects) and testing methods can be found in
,
2 3 Substrates by Nitric Acid Vapor
literature. An ASTM guide to the selection of porosity and
B 741 Test Method for Porosity in Gold Coatings on Metal
gross defect tests for electrodeposits and related metallic
Substrates by Paper Electrography
coatings is available as Guide B 765. Other related porosity test
B 765 Guide to the Selection of Porosity Tests for Elec-
standards are Test Methods B 735, B 741, B 798, B 799, and
trodeposits and Related Coatings
B 809.
B 798 Test Method for Porosity in Gold or Palladium
1.4 The values stated in SI units are to be regarded as the
Coatings on Metal Substrates by Gel-Bulk Electrography
standard. The values given in parentheses are for information
B 799 Test Method for Porosity in Gold and Palladium
only.
Coatings by Sulfurous Acid/Sulfur Dioxide Vapor
1.5 This standard does not purport to address all of the
B 809 Test Method for Porosity in Metallic Coatings by
safety concerns, if any, associated with its use. It is the
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3. Terminology
bility of regulatory limitations prior to use.
3.1 Definitions: Many terms used in this test method are
2. Referenced Documents defined in Terminologies B 374 or B 542.
3.2 Definitions of Terms Specific to This Standard:
2.1 ASTM Standards:
3.2.1 defect indications—black or dark colored products
B 246 Specification for Tinned Hard-Drawn and Medium-
resulting from the reaction between the alkaline polysulfide
Hard Drawn Copper Wire for Electrical Purposes
5 reagent and exposed copper or copper alloy underlying metal.
B 374 Terminology Relating to Electroplating
3.2.2 gross defects—breaks in the coating that expose rela-
B 488 Specification for Electrodeposited Coatings of Gold
5 tively large areas of underlying metal to the environment
for Engineering Uses
(compare with intrinsic porosity (3.2.3)). Gross defects include
those produced by mechanical damage and wear, in addition to
as-plated large pores (with diameters an order of magnitude
This test method is under the jurisdiction of ASTM Committee B08 on Metallic greater than intrinsic porosity) and networks of microcracks.
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
NOTE 1—Such large pores and microcrack networks indicate serious
General Test Methods.
Current edition approved Oct. 10, 1995. Published December 1995. deviations from acceptable coating practice (as, for example, dirty
Clarke, M., “Porosity and Porosity Tests,” in Properties of Electrodeposits,
basis-metal substrates and contaminated or out-of-balance plating baths).
edited by Sard, Leidheiser, and Ogburn, The Electrochemical Society, 1975, p. 122.
3.2.3 intrinsic porosity—the 88normal” porosity that is
Krumbein, S. J., “Porosity Testing of Contact Platings,” Trans. Connectors and
Interconnection Technology Symposium, Philadelphia, PA, October 1987, p. 47. present, to some degree, in all commercial thin platings (such
Annual Book of ASTM Standards, Vol 02.03.
Annual Book of ASTM Standards, Vol 02.05.
Annual Book of ASTM Standards, Vol 03.04.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information. Contact ASTM International (www.astm.org) for the latest information.
B 866
as in precious-metal coatings for engineering purposes) and in any post-plating operation or even towards the end of the
will generally follow an inverse relationship with thickness. plating operation. It is most often seen to occur in product
assembly operations.
NOTE 2—Intrinsic porosity is due primarily to small deviations from
5.5 If properly performed, this test will also detect wear-
ideal plating and surface preparation conditions. Scanning electron mi-
through, provided the wear-through reaches a copper or
croscope (SEM) studies have shown that the diameter of such pores, at the
plating surface, is of the order of micrometres, so that only small areas of copper-alloy layer.
underlying metal are exposed to the environment.
5.6 Many types of gross defects are too small to be seen,
except at magnifications so high (as in SEM) that a realistic
3.2.4 measurement area—the portion or portions of the
assessment of the measurement area cannot be easily made.
surface examined for the presence of gross defects or mechani-
Other defects, such as many types of wear-through, provide
cal damage (and wear-through). The measurement area shall be
insufficient contrast with the coating surface. Gross defects
indicated on the drawings of the parts, or by the provision of
tests (as with porosity tests) are, therefore, used to magnify the
suitably marked samples.
defect sites by producing visible reaction products in and
3.2.5 metallic coatings—platings, claddings, or other metal-
around the defects.
lic coatings applied to the basis-metal substrate. The coating
5.7 The polysulfide solution will react with copper and
can comprise a single metallic layer or a combination of
copper alloys to produce a dark brown or black stain (the defect
metallic layers.
indications) at the site of the defect. Silver also turns black
3.2.6 porosity (general)—in a coating, the presence of any
under the same conditions. The test solution will not react with
hole, crack, or other defect that exposes the underlying metal to
nickel and is only useful when the presence or absence of
the environment.
copper exposure is a specific requirement.
3.2.7 underplate—a metallic coating layer between the
5.8 The polysulfide immersion test is relatively insensitive
basis metal and the topmost metallic coating. The thickness of
an underplating is usually greater than 1 μm, in contrast to a to the presence of small pores. It shall not be used as a general
porosity test. (Test Method B 809 should be used instead.)
strike or flash, which is usually thinner.
3.2.8 wear-through—the exposure of underplate or basis 5.9 The extent and location of the gross defects or mechani-
metal as a direct result of wear. Wear-through is an observable cal damage (revealed by this test) may or may not be
phenomenon. detrimental to product performance or service life. Such
3.2.9 wear track—a mark that indicates the path along determinations shall be made by the user of the test through
which physical contact had been made during a sliding process practical experience or judgment.
(such as the mating and unmating of an electrical contact). 5.10 The present test can be used on samples of various
geometries, such as curved surfaces. It can also be used for
4. Summary of Test Method
selective area coating if allowance is made for tarnish creepage
4.1 The test samples are immersed in an alkaline polysulfide
from bare copper alloy areas.
solution at 74°C (165°F) for 60 s. After rinsing and drying, the
5.11 This test is destructive in that it reveals the presence of
samples are examined for dark or discolored areas which
gross defects by contaminating the surface with reaction-
indicate exposure of copper or copper alloys to the solution
product films. Any parts exposed to this test shall not be placed
through breaks in the coating.
in service.
5.12 However, the defect indications on the sample surfaces
5. Significance and Use
that result from this test are stable; samples may be retained for
5.1 The purpose of the alkaline polysulfide immersion test is
reference purposes.
to determine the presence of mechanical damage, wear-
5.13 This test is neither recommended for predictions of
through, and other gross defects in the coating. Most metallic
product performance nor is it intended to simulate field failure
coatings are intended to be protective and the presence of gross
mechanisms. For such product performance evaluations, an
defects indicates a serious reduction of such protection.
environmental test that is known to simulate actual failure
5.2 The protection afforded by well applied coatings may be
mechanisms should be used.
diminished by improper handling following plating or as a
result of wear or mechanical damage during testing or while in
6. Apparatus
service. The alkaline polysulfide test serves to indicate if the
6.1 In addition to the normal equipment (beakers, bottles,
damage has extended down to the copper or copper alloy basis
weighing balances, funnels, and so forth) that are part of every
metal since it will not detect exposed nickel underplate.
chemical laboratory, the following apparatus are required:
5.3 The alkaline polysulfide test has been specified in
6.1.1 Microscope—Optical, stereo, 10 to 303. It is pre-
several ASTM specifications for tin-plated coatings, namely
ferred that one eyepiece contain a graduated reticle for mea-
Specifications B 246 and B 545. This test could also be used to
suring the diameter of tarnish spots. The reticle shall be
detect gross defects and mechanical damage in other metallic
calibrated for the magnification at which the microscope is to
coatings, such as tin-nickel alloy (Specification B 605), nickel
be used, preferably 103.
(Specification B 689), gold (Specification B 488), palladium
(Specification B 679), and autocatalytic nickel-phosphorous 6.1.2 Hydrometer, 1.120 to 1.190 specific gravity, 150–mm
scale.
coatings (Specification B 733).
5.4 This test detects mechanical damage that exposes cop- 6.1.3 Light Source (Illuminator) for Microscope, incandes-
per underplate and copper basis metal. Such damage may occur cent, or circular fluorescent.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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B 866
7. Reagents 9.2.1 Handle samples as little as possible, even before
cleaning, and only with tweezers, microscope-lens tissue, or
7.1 Sodium Hydroxide, pellet, ACS certified grade or better.
clean soft cotton gloves.
7.2 Sodium Sulfide, 9-hydrate, ACS “Analytical Reagent”
9.2.2 Before being cleaned, the samples shall be prepared so
(AR) grade, or better.
that the measurement areas may be viewed easily through the
7.3 Sulfur, precipitated, USP grade.
microscope. If samples are part of assembled products, they
8. Hazards
may need to be disassembled to ensure proper access to these
areas and to enable the part to be immersed in the alkaline
8.1 All of the normal precautions shall be observed in
handling the materials required for this test. This shall also polysulfide solution.
include, but not be limited to, procuring and reviewing
NOTE 3—Since the test is specific to the plated metallic portions of the
Material Safety Data Sheets that meet the minimum require-
product, the latter should be separated from plastic housings, etc.,
ments of the OSHA Hazard Communication Standard for all
whenever possible, before cleaning. Also, nonmetallic materials, such as
chemicals used in cleaning and testing, and observing the paper tags, string, tape, and so forth, shall be removed, but take care to
maintain sample identity.
recommendations given.
9.2.3 Cleaning:
9. Preparation
9.2.3.1 Inspect the samples under 103 magnification for
9.1 Preparation of Solutions:
evidence of particulate matter. If present, such particles should
9.1.1 Polysulfide Solution—Warning—All work shall be
be removed by “dusting” (that is, blowing them off the sample)
done under an operating fume hood since the gases emitted and
with clean, oil-free air.
the polysulfide solution are toxic.
9.2.3.2 Thoroughly clean the particle-free samples with
9.1.1.1 Make a saturated solution of sodium sulfide by
solvents or solutions that do not contain CFCs, chlorinated
dissolving 20 to 25 g of sodium sulfide in 100 mL of deionized
hydrocarbons, or other known ozone-destroying compounds.
or distilled water. Stir for 30 min at minimum. Make sure that
The procedure outlined in Note 4 has been found to give
undissolved crystals are present in the solution. If not present,
satisfactory results for coatings with mild to moderate surface
continue adding increments of approximately 0.5–g sodium
contamination.
sulfide, with stirring, until the solution is saturated (excess
NOTE 4—Suggested Cleaning Procedure:
solids present).
(1) Keep individual pieces separated if there is a possibility of damage
9.1.1.2 With stirring, slowly add 30 to 35 g of sulfur to the
to the measurement areas during the various cleaning steps.
saturated sodium sulfide solution.
(2) Clean samples for 5 min in an ultrasonic cleaner which contains a
9.1.1.3 Cover the beaker. Stir for 60 min at minimum.
hot (65 to 85°C) 2 % aque
...