ASTM B877-96(2003)
(Test Method)Standard Test Method for Gross Defects and Mechanical Damage in Metallic Coatings by the Phosphomolybdic Acid (PMA) Method
Standard Test Method for Gross Defects and Mechanical Damage in Metallic Coatings by the Phosphomolybdic Acid (PMA) Method
SCOPE
1.1 This test standard covers equipment and methods for using phosphomolybdic acid (PMA) to detect gross defects and mechanical damage including wear through in metallic coatings of gold, silver, or palladium. These metals comprise the topmost metallic layers over substrates of nickel, copper, or copper alloys.
1.2 Recent reviews of porosity testing, which include those for gross defects, and testing methods can be found in the lierature. An ASTM guide to the selection of porosity and gross defect tests for electrodeposits and related metallic coatings is available as Guide B 765. Other related porosity and gross defects test standards are Test Methods B 735, B 741, B 798, B 799, B 809, and B 866.
1.3 The values stated in SI units are the preferred units. Those in parentheses are for information only.
1.4 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.
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Designation:B877–96 (Reapproved 2003)
Standard Test Method for
Gross Defects and Mechanical Damage in Metallic Coatings
by the Phosphomolybdic Acid (PMA) Method
This standard is issued under the fixed designation B 877; 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 689 Specification for Electroplated Engineering Nickel
Coatings
1.1 This test standard covers equipment and methods for
B 735 Test Method for Porosity in Gold Coatings on Metal
usingphosphomolybdicacid(PMA)todetectgrossdefectsand
Substrates by Nitric Acid Vapor
mechanical damage including wear through in metallic coat-
B 741 Test Method for Porosity in Gold Coatings on Metal
ings of gold, silver, or palladium. These metals comprise the
Substrates by Paper Electrography
topmost metallic layers over substrates of nickel, copper, or
B 765 Guide for Selection of Porosity Tests for Electrode-
copper alloys.
posits and Related Metallic Coatings
1.2 Recent reviews of porosity testing, which include those
B 798 Test Method for Porosity in Gold or Palladium
for gross defects, and testing methods can be found in the
,
2 3 Coatings on Metal Substrates by Gel-Bulk Electrography
literature. An ASTM guide to the selection of porosity and
B 799 Test Method for Porosity in Gold and Palladium
gross defect tests for electrodeposits and related metallic
Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
coatings is available as Guide B 765. Other related porosity
B 809 Test Method for Porosity in Metallic Coatings by
and gross defects test standards are Test Methods B 735,
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
B 741, B 798, B 799, B 809, and B 866.
B 866 Test Method for Gross Defects and Mechanical
1.3 The values stated in SI units are the preferred units.
Damage in Metallic Coatings by Polysulfide Immersion
Those in parentheses are for information only.
1.4 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions—Many terms in this test method are defined
responsibility of the user of this standard to establish appro-
in Terminology B 374 or B 542.
priate safety and health practices and determine the applica-
3.2 Definitions of Terms Specific to This Standard:
bility of regulatory limitations prior to use.
3.2.1 base metal, n—any metal other than gold, silver,
2. Referenced Documents platinum, palladium, iridium, or rhodium. Typical base metals
used as underplates or substrates are copper, nickel, tin, lead,
2.1 ASTM Standards:
and their alloys.
B 374 Terminology Relating to Electroplating
3.2.2 defect indications, n—colored droplets resulting from
B 488 Specification for Electrodeposited Coatings of Gold
the reaction between the PMA reagent and the underlying
for Engineering Uses
metal.
B 542 Terminology Relating to Electrical Contacts and
3.2.3 gross defects, n—those breaks in the coating that
Their Use
expose relatively large areas of underlying metal to the
B 679 Specification for Electrodeposited Coatings of Palla-
environment. Gross defects include those produced by me-
dium for Engineering Use
chanicaldamageandwear,aswellasas-platedlargeporeswith
diameters an order of magnitude greater than intrinsic porosity
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
and networks of microcracks.
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
Test Methods.
NOTE 1—Large pores and microcrack networks indicate serious devia-
Current edition approved Feb. 10, 2003. Published May 2003. Originally
tions from acceptable coating practice (dirty substrates and contaminated
approved in 1996. Last previous edition approved in 1996 as B 877 – 96.
or out-of-balance plating baths).
Clarke, M., “Porosity and Porosity Tests,” Properties of Electrodeposits, ed. by
Sand, Leidheiser, and Ogburn, The Electrochemical Society, 1975, p. 122. 3.2.4 intrinsic porosity, n—the normal porosity that is
Krumbein, S. J., “Porosity Testing of Contact Platings,” Trans. Connectors and
present, to some degree, in all commercial thin electrodeposits
Interconnection Technology Symposium, Philadelphia, PA, October 1987, p. 47.
(precious metal coatings for engineering purposes) that will
Annual Book of ASTM Standards, Vol 02.05.
generally follow an inverse relationship with thickness.
Annual Book of ASTM Standards, Vol 02.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B877–96 (2003)
NOTE 2—Intrinsic porosity is due to small deviations from ideal plating
result of wear or mechanical damage during testing or while in
and surface preparation conditions. Scanning electron microscope (SEM)
service. The PMA test can serve to indicate the existence of
studies have shown the diameter of such pores at the plating surface is 1
such damage.
to 2 µm so only small areas of underlying metal are exposed to the
5.3 This test is used to detect underplate and substrate metal
environment.
exposed through normal wear during relative motions (mating
3.2.5 measurement area, n—that portion or portions of the
of electrical contacts) or through mechanical damage.As such,
surface that is examined for the presence of gross defects or
it is a sensitive pass/fail test and, if properly performed, will
mechanical damage and wear through. The measurement area
rapidly detect wear through to base metals or scratches that
shall be indicated on the drawings of the parts or by the
enter the base metal layers.
provision of suitably marked samples.
5.4 This test is relatively insensitive to small pores. It is not
3.2.6 metallic coatings, n—include electrodeposits, clad-
designed to be a general porosity test and shall not be used as
dings, or other metallic layers applied to the substrate. The
such. The detection of pores will depend upon their sizes and
coating can comprise a single metallic layer or a combination
the length of time that the reagent remains a liquid.
of metallic layers (gold over palladium).
5.5 This test cannot distinguish degrees of wear through or
3.2.7 porosity (general), n—thepresenceofanyhole,crack,
whether the wear through is to nickel or copper. Once base
or other defect that exposes the underlying metal to the
metal is exposed, the colored molybdenum complex is formed.
environment.
Whilerelativelysmallareadefects(comparedtotheareaofthe
3.2.8 underplate, n—a metallic coating layer between the
droplet) may be seen at the bottom of the drop as tiny colored
substrate and the topmost metallic coating. The thickness of an
regions immediately after applying the PMA, any larger areas
underplate is usually greater than 1 µm, in contrast to a strike
of exposed base metal will cause the entire droplet to turn dark
or flash, which is usually thinner.
instantly.
3.2.9 wear through, n—the exposure of underplate or sub-
5.6 The PMA test also detects mechanical damage that
strate as a direct result of wear. Wear through is an observable
exposes underplate and substrate metal. Such damage may
phenomenon.
occur in any postplating operation or even at the end of the
3.2.10 wear track, n—a mark that indicates the path along
plating operation. It can often occur in assembly operations
which physical contact has been made during a sliding process
where plated parts are assembled into larger units by mechani-
(the mating and unmating of an electrical contact).
cal equipment.
4. Summary of Test Method
5.7 The PMA test identifies the locations of exposed base
metal. The extent and location of these exposed areas may or
4.1 This test method involves the use of a solution of
may not be detrimental to performance. The PMA test is not
phosphomolybdic acid (PMA), which is a solid complex of
recommended for predictions of product performance, nor is it
molybdenum trioxide, Mo O , and phosphoric acid, H PO .In
2 3 3 4
intended to simulate field failure mechanisms. For such contact
this state, molybdenum is very reactive with many free metals
performance evaluations, an environmental test known to
and may be used to detect exposed underplates and substrate
simulate actual failure mechanisms should be used.
metals. The part is exposed briefly to fumes of hydrochloric
5.8 The PMAtest is primarily intended for the evaluation of
acid to remove oxides in the defect region.Asmall drop of the
individual samples rather than large sample lots, since evalu-
aqueous PMA solution is applied to the spot in question using
ations are normally carried out one at a time under the
an applicator. If it contacts base metals from exposed under-
microscope (see Section 10).
plate or substrate, the Mo O will immediately be reduced to
2 3
5.9 This test is destructive. Any parts exposed to the PMA
lower oxides, forming the intensely colored, molybdenum blue
complex (heteropoly blue). test shall not be placed in service.
4.2 This test may not be suitable for some precious metal
alloy coatings that contain significant concentrations of non- 6. Apparatus
precious metals (base metals) like nickel or copper. (See .)
6.1 In addition to the normal equipment (beakers, weighing
4.3 The reagents in this test also react with tin, lead, and
balances, funnels, etc.) that are a part of every chemical
tin-lead solder.
laboratory.
6.2 Microscope, Optical, Stereo, 10 to 303—It is preferred
5. Significance and Use
that one eyepiece contain a graduated reticle for measuring the
5.1 The primary purpose of the PMAtest is to determine the
defect location. The reticle shall be calibrated for the magni-
presence of mechanical damage, wear through, and other gross
fication at which the microscope is to be used, preferably
defects in the coating. Most metallic coatings are intended to
103.
be protective, and the presence of gross defects indicates a
6.3 Lightsource(illuminator)formicroscope,incandescent.
serious reduction of such protection.
6.4 Glass volumetric flask, 10 mL.
5.2 The protection afforded by well applied coatings may be
diminished by improper handling following plating or as a
Magnification standards suitable for calibrating optical microscopes may be
Van Wazer, J. P., Phosphorous and Its Compounds, Interscience Publishers, purchased from U.S. National Institute of Standards and Technology, Office of
New York, 1961. Standard Reference Materials.
B877–96 (2003)
the bottom of the flask. This indicates saturation.
6.5 Glassbottleofastableshapeandwithglassstopper.The
bottle opening shall be 2.5 cm (1 in) minimum.An example is
9.1.3.3 Pour into a clean bottle and label bottle with
a 50-mL low-form weighing bottle or a flask-shaped weighing
contents and preparation date.
bottle.
9.1.3.4 Solution may be used for one week. Store in
6.6 Applicators (see 9.2)—Platinum wire, 32 AWG, or
refrigerator when not in use.
disposable glass micropipets, 1 or 0.5 µL size.
9.1.4 Hydrochloric acid (for both methods):
9.1.4.1 Fill the special glass bottle (see 6.4) to approxi-
7. Reagents and Materials
mately halfway from the top.
7.1 Phosphomolybdic Acid (PMA)—Crystalline,ACS certi-
9.1.4.2 Label glass bottle with contents.
fied grade.
9.1.4.3 Keep stoppered and under a fume hood when not in
7.2 Concentrated Hydrochloric Acid— ACS analytical re-
use.
agent (AR) grade or better.
9.2 Preparation of applicators:
9.2.1 The applicator shall not react with the PMA solution.
8. Specific Safety and Health Precautions
Examples are as follows:
8.1 Allthenormalprecautionsshallbeobservedinhandling
9.2.1.1 Platinum—Make a small loop using a 32 AWG
the materials required for this test.This shall include, but is not
platinum wire and an appropriate size mandrel (such as a
limited to, procuring and reviewing Material Safety Data
needle). Leave a small gap to facilitate release of the PMA
Sheets that meet the minimum requirements of the OSHA
droplet (see Fig. 1).Attach loop to a wooden or plastic handle.
Hazard Communication Standard for all chemicals used in
9.2.1.2 Platinum inoculating loops with handles may be
cleaning and testing and observing the recommendations
purchased. Cut the loop with a knife to create a small gap (Fig.
given.
1), which will facilitate the release of the PMA droplet.
9.2.1.3 Glass capillary micropipets in the 1-µL size or
9. Preparations
smaller.
9.1 Preparation of solutions:
9.2.2 If a platinum loop is used as the applicator, the loop
9.1.1 Two types of PMA solutions can be used with this diameter shall preferably be 1 mm and shall not exceed 2 mm.
method.
The loop diameter is kept small for the following reasons:
9.1.1.1 Method A, the preferred method, uses a dilute 8 % 9.2.2.1 The small dimensions of many examination areas.
solution of PMA in water.
9.2.2.2 The ability of the loop to release a rounded droplet
9.1.1.2 Method B, uses a saturated solution of PMA in instead of a thin sheet of solution, which dries too fast.
water.
9.2.2.3 Difficulty in controlling flow and observing reac-
tions in large drops.
NOTE 3—The dilute solution is preferred because it works well with
9.3 Preparation of test samples:
silver, gold, and palladium coatings, while the saturated solution reacts
9.3.1 Handle samples as little as possible even prior to
with silver to give false indications. In addition, the saturated solution has
cleaning and only with tweezers, microscope-lens tissue, or
a tendency to dry up quickly on the test surface before proper evaluations
can be made.
clean, soft cotton gloves.
9.3.2 Prior to being cleaned, the samples shall be prepared
9.1.2 Dilute (8 %) PMA solution (for Method A):
so the measurement area is accessible and can be placed in a
9.1.2.1 Place a small, clean, and dry glass funnel in the neck
basically horizontal plane. This allows for easy viewing
of a clean, dry 10 mL volumetric flask.
through the microscope and prevents the PMA solution from
9.1.2.2 Tare out the weight of the funnel and flask on a
running off during application.
balance.
9.3.3 Masking:
9.1.2.3 Weigh 0.8 (60.1) g PMA into the flask, using a
9.3.3.1 The PMA solution will react with any exposed base
plastic or glass spatula.
metal such as nickel, copper, tin, lead, or solder. If the
9.1.2.4 Rinse the funnel with distilled or deionized water to
examination area is within a millimetre of exposed or thinly
drain any adhering PMA into the flask.
plated substrate metal, masking may be necessary.
9.1.2.5 Dilute to mark with deionized water.
9.3.3.2 If masking is necessary, clean per 9.3.4. Carefully
9.1.2.6 Place stopper in flask and mix thoroughly. Cloudy
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