ASTM B877-96(2008)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B877 − 96(Reapproved 2008)
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 B877; 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 B542Terminology Relating to Electrical Contacts andTheir
Use
1.1 This test standard covers equipment and methods for
B679Specification for Electrodeposited Coatings of Palla-
usingphosphomolybdicacid(PMA)todetectgrossdefectsand
dium for Engineering Use
mechanical damage including wear through in metallic coat-
B689Specification for Electroplated Engineering Nickel
ings of gold, silver, or palladium. These metals comprise the
Coatings
topmost metallic layers over substrates of nickel, copper, or
B735Test Method for Porosity in Gold Coatings on Metal
copper alloys.
Substrates by Nitric Acid Vapor
1.2 Recent reviews of porosity testing, which include those
B741Test Method for Porosity In Gold Coatings On Metal
for gross defects, and testing methods can be found in the
Substrates By Paper Electrography (Withdrawn 2005)
2,3
literature. An ASTM guide to the selection of porosity and
B765GuideforSelectionofPorosityandGrossDefectTests
gross defect tests for electrodeposits and related metallic
for Electrodeposits and Related Metallic Coatings
coatingsisavailableasGuideB765.Otherrelatedporosityand
B798Test Method for Porosity in Gold or Palladium Coat-
gross defects test standards are Test Methods B735, B741,
ings on Metal Substrates by Gel-Bulk Electrography
B798, B799, B809, and B866, Specifications B488, B679,and
B799Test Method for Porosity in Gold and Palladium
B689.
Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
1.3 The values stated in SI units are the preferred units. B809Test Method for Porosity in Metallic Coatings by
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
Those in parentheses are for information only.
B866Test Method for Gross Defects and Mechanical Dam-
1.4 This standard does not purport to address all of the
age in Metallic Coatings by Polysulfide Immersion
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3. Terminology
priate safety and health practices and determine the applica-
3.1 Definitions—Many terms in this test method are defined
bility of regulatory limitations prior to use.
in Terminology B374 or B542
2. Referenced Documents
3.2 Definitions of Terms Specific to This Standard:
2.1 ASTM Standards: 3.2.1 base metal, n—any metal other than gold, silver,
B374Terminology Relating to Electroplating platinum, palladium, iridium, or rhodium. Typical base metals
B488Specification for Electrodeposited Coatings of Gold used as underplates or substrates are copper, nickel, tin, lead,
for Engineering Uses and their alloys.
3.2.2 defect indications, n—colored droplets resulting from
the reaction between the PMA reagent and the underlying
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
metal.
and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.10 on
3.2.3 gross defects, n—those breaks in the coating that
Test Methods.
Current edition approved Aug. 1, 2008. Published September 2008. Originally
expose relatively large areas of underlying metal to the
approved in 1996. Last previous edition approved in 2003 as B877–96 (2003).
environment. Gross defects include those produced by me-
DOI: 10.1520/B0877-96R08.
chanicaldamageandwear,aswellasas-platedlargeporeswith
Clarke,M.,“PorosityandPorosityTests,” Properties of Electrodeposits,ed.by
diameters an order of magnitude greater than intrinsic porosity
Sand, Leidheiser, and Ogburn, The Electrochemical Society, 1975, p. 122.
Krumbein, S. J., “PorosityTesting of Contact Platings,”Trans. Connectors and
and networks of microcracks.
Interconnection Technology Symposium, Philadelphia, PA, October 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 last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B877 − 96 (2008)
NOTE 1—Large pores and microcrack networks indicate serious devia-
5. Significance and Use
tions from acceptable coating practice (dirty substrates and contaminated
5.1 TheprimarypurposeofthePMAtestistodeterminethe
or out-of-balance plating baths).
presenceofmechanicaldamage,wearthrough,andothergross
3.2.4 intrinsic porosity, n—the normal porosity that is pres-
defects in the coating. Most metallic coatings are intended to
ent, to some degree, in all commercial thin electrodeposits
be protective, and the presence of gross defects indicates a
(precious metal coatings for engineering purposes) that will
serious reduction of such protection.
generally follow an inverse relationship with thickness.
5.2 Theprotectionaffordedbywellappliedcoatingsmaybe
NOTE2—Intrinsicporosityisduetosmalldeviationsfromidealplating
diminished by improper handling following plating or as a
and surface preparation conditions. Scanning electron microscope (SEM)
resultofwearormechanicaldamageduringtestingorwhilein
studies have shown the diameter of such pores at the plating surface is 1
to 2 µm so only small areas of underlying metal are exposed to the
service. The PMA test can serve to indicate the existence of
environment.
such damage.
3.2.5 measurement area, n—that portion or portions of the
5.3 Thistestisusedtodetectunderplateandsubstratemetal
surface that is examined for the presence of gross defects or
exposed through normal wear during relative motions (mating
mechanical damage and wear through. The measurement area
of electrical contacts) or through mechanical damage.As such,
shall be indicated on the drawings of the parts or by the
it is a sensitive pass/fail test and, if properly performed, will
provision of suitably marked samples.
rapidly detect wear through to base metals or scratches that
3.2.6 metallic coatings, n—include electrodeposits, clad-
enter the base metal layers.
dings, or other metallic layers applied to the substrate. The
5.4 This test is relatively insensitive to small pores. It is not
coating can comprise a single metallic layer or a combination
designed to be a general porosity test and shall not be used as
of metallic layers (gold over palladium).
such. The detection of pores will depend upon their sizes and
3.2.7 porosity (general), n—thepresenceofanyhole,crack,
the length of time that the reagent remains a liquid.
or other defect that exposes the underlying metal to the
5.5 This test cannot distinguish degrees of wear through or
environment.
whether the wear through is to nickel or copper. Once base
3.2.8 underplate, n—a metallic coating layer between the
metalisexposed,thecoloredmolybdenumcomplexisformed.
substrateandthetopmostmetalliccoating.Thethicknessofan
Whilerelativelysmallareadefects(comparedtotheareaofthe
underplate is usually greater than 1 µm, in contrast to a strike
droplet) may be seen at the bottom of the drop as tiny colored
or flash, which is usually thinner.
regions immediately after applying the PMA, any larger areas
3.2.9 wear through, n—the exposure of underplate or sub- ofexposedbasemetalwillcausetheentiredroplettoturndark
strate as a direct result of wear. Wear through is an observable
instantly.
phenomenon.
5.6 The PMA test also detects mechanical damage that
3.2.10 wear track, n—a mark that indicates the path along
exposes underplate and substrate metal. Such damage may
which physical contact has been made during a sliding process
occur in any postplating operation or even at the end of the
(the mating and unmating of an electrical contact).
plating operation. It can often occur in assembly operations
where plated parts are assembled into larger units by mechani-
4. Summary of Test Method
cal equipment.
4.1 This test method involves the use of a solution of
5.7 The PMA test identifies the locations of exposed base
phosphomolybdic acid (PMA), which is a solid complex of
metal. The extent and location of these exposed areas may or
molybdenumtrioxide,Mo O ,andphosphoricacid,H PO.In
2 3 3 4 may not be detrimental to performance. The PMA test is not
this state, molybdenum is very reactive with many free metals
recommended for predictions of product performance, nor is it
and may be used to detect exposed underplates and substrate
intendedtosimulatefieldfailuremechanisms.Forsuchcontact
metals. The part is exposed briefly to fumes of hydrochloric
performance evaluations, an environmental test known to
acid to remove oxides in the defect region.Asmall drop of the
simulate actual failure mechanisms should be used.
aqueous PMAsolution is applied to the spot in question using
5.8 ThePMAtestisprimarilyintendedfortheevaluationof
an applicator. If it contacts base metals from exposed under-
individual samples rather than large sample lots, since evalu-
plate or substrate, the Mo O will immediately be reduced to
2 3
ations are normally carried out one at a time under the
loweroxides,formingtheintenselycolored,molybdenumblue
microscope (see Section 10).
complex (heteropoly blue).
5.9 This test is destructive. Any parts exposed to the PMA
4.2 This test may not be suitable for some precious metal
test shall not be placed in service.
alloy coatings that contain significant concentrations of non-
precious metals (base metals) like nickel or copper. (See .)
6. Apparatus
4.3 The reagents in this test also react with tin, lead, and
6.1 In addition to the normal equipment (beakers, weighing
tin-lead solder.
balances, funnels, etc.) that are a part of every chemical
laboratory.
6.2 Microscope, Optical, Stereo, 10 to 30× —It is preferred
Van Wazer, J. P., Phosphorous and Its Compounds, Interscience Publishers,
New York, 1961. that one eyepiece contain a graduated reticle for measuring the
B877 − 96 (2008)
defect location. The reticle shall be calibrated for the magni- 9.1.2.7 Pour clear solution into a clean glass bottle and seal
ficationatwhichthemicroscopeistobeused,preferably10×. with glass stopper. Label bottle with PMA concentration and
date of preparation.
6.3 Lightsource(illuminator)formicroscope,incandescent.
9.1.2.8 Storebottleinrefrigerator.Solutionmaybeusedfor
6.4 Glass volumetric flask, 10 mL.
one week.
6.5 Glassbottleofastableshapeandwithglassstopper.The 9.1.3 Saturated PMA solution (for Method B):
9.1.3.1 Prepare solution in accordance with 9.1.2.1-9.1.2.6,
bottle opening shall be 2.5 cm (1 in) minimum.An example is
a 50-mLlow-form weighing bottle or a flask-shaped weighing except use approximately5gofPMAinstead of 0.8 g. (Filter
out sediment, if necessary.)
bottle.
9.1.3.2 Mix thoroughly for at least 10 min.
6.6 Applicators (see 9.2)—Platinum wire, 32 AWG, or
disposable glass micropipets, 1 or 0.5 µL size. NOTE 4—There shall be a small excess of PMA, seen as a sediment in
the bottom of the flask. This indicates saturation.
7. Reagents and Materials
9.1.3.3 Pour into a clean bottle and label bottle with
contents and preparation date.
7.1 Phosphomolybdic Acid (PMA)—Crystalline, ACS certi-
9.1.3.4 Solution may be used for one week. Store in
fied grade.
refrigerator when not in use.
7.2 Concentrated Hydrochloric Acid— ACS analytical re-
9.1.4 Hydrochloric acid (for both methods):
agent (AR) grade or better.
9.1.4.1 Fill the special glass bottle (see 6.4) to approxi-
mately halfway from the top.
8. Specific Safety and Health Precautions
9.1.4.2 Label glass bottle with contents.
8.1 Allthenormalprecautionsshallbeobservedinhandling 9.1.4.3 Keep stoppered and under a fume hood when not in
thematerialsrequiredforthistest.Thisshallinclude,butisnot use.
limited to, procuring and reviewing Material Safety Data
9.2 Preparation of applicators:
Sheets that meet the minimum requirements of the OSHA
9.2.1 The applicator shall not react with the PMAsolution.
Hazard Communication Standard for all chemicals used in
Examples are as follows:
cleaning and testing and observing the recommendations
9.2.1.1 Platinum—Make a small loop using a 32 AWG
given.
platinum wire and an appropriate size mandrel (such as a
needle). Leave a small gap to facilitate release of the PMA
9. Preparations
droplet (see Fig. 1).Attach loop to a wooden or plastic handle.
9.1 Preparation of solutions: 9.2.1.2 Platinum inoculating loops with handles may be
9.1.1 Two types of PMA solutions can be used with this purchased.Cuttheloopwithaknifetocreateasmallgap(Fig.
method. 1), which will facilitate the release of the PMA droplet.
9.1.1.1 Method A, the preferred method, uses a dilute 8% 9.2.1.3 Glass capillary micropipets in the 1-µL size or
solution of PMA in water. smaller.
9.2.2 If a platinum loop is used as the applicator, the loop
9.1.1.2 Method B, uses a saturated solution of PMA in
water. diameter shall preferably be 1 mm and shall not exceed 2 mm.
The loop diameter is kept small for the following reasons:
NOTE 3—The dilute solution is preferred because it works well with
9.2.2.1 The small dimensions of many examination areas.
silver, gold, and palladium coatings, while the saturated solution reacts
9.2.2.2 The ability of the loop to release a rounded droplet
withsilvertogivefalseindications.Inaddition,thesaturatedsolutionhas
a tendency to dry up quickly on the test surface before proper evaluations
instead of a thin sheet of solution, which dries too fast.
can be made.
9.2.2.3 Difficulty in controlling flow and observing reac-
9.1.2 Dilute (8%) PMA solution (for Method A): tions in large drops.
9.1.2.1 Placeasmall,clean,anddryglassfunnelintheneck
9.3 Preparation of test samples:
of a clean, dry 10 mL volumetric flask.
9.3.1 Handle samples as little as possible even prior to
9.1.2.2 Tare out the weight of the funnel and flask on a
cleaning and only with tweezers, microscope-lens tissue, or
balance.
clean, soft cotton gloves.
9.1.2.3 Weigh 0.8 (60.1) g PMA into the flask, using a
9.3.2 Prior to being cleaned, the samples shall be prepared
plastic or glass spatula.
so the measurement area is accessible and can be placed in a
9.1.2.4 Rinse the funnel with distilled or deionized water to
drain any adhering PMA into the flask.
9.1.2.5 Dilute to mark with deionized water.
9.1.2.6 Place stopper in flask and mix thoroughly. Cloudy
solution will clear a
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