1、Designation: B 877 96 (Reapproved 2008)Standard Test Method forGross Defects and Mechanical Damage in Metallic Coatingsby the Phosphomolybdic Acid (PMA) Method1This standard is issued under the fixed designation B 877; the number immediately following the designation indicates the year oforiginal ad
2、option or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test standard covers equipment and methods forusing phosphomolybd
3、ic acid (PMA) to detect gross defects andmechanical damage including wear through in metallic coat-ings of gold, silver, or palladium. These metals comprise thetopmost metallic layers over substrates of nickel, copper, orcopper alloys.1.2 Recent reviews of porosity testing, which include thosefor gr
4、oss defects, and testing methods can be found in theliterature.2,3An ASTM guide to the selection of porosity andgross defect tests for electrodeposits and related metalliccoatings is available as Guide B 765. Other related porosityand gross defects test standards are Test Methods B 735,B 741, B 798,
5、 B 799, B 809, and B 866, Specifications B 488,B 679,and B 689.1.3 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 thesafety concerns, if any, associated with its use. It is theresponsibility of
6、the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:4B 374 Terminology Relating to ElectroplatingB 488 Specification for Electrodeposited Coatings of Goldfor
7、Engineering UsesB 542 Terminology Relating to Electrical Contacts andTheir UseB 679 Specification for Electrodeposited Coatings of Palla-dium for Engineering UseB 689 Specification for Electroplated Engineering NickelCoatingsB 735 Test Method for Porosity in Gold Coatings on MetalSubstrates by Nitri
8、c Acid VaporB 741 Test Method for Porosity In Gold Coatings On MetalSubstrates By Paper Electrography5B 765 Guide for Selection of Porosity and Gross DefectTests for Electrodeposits and Related Metallic CoatingsB 798 Test Method for Porosity in Gold or PalladiumCoatings on Metal Substrates by Gel-Bu
9、lk ElectrographyB 799 Test Method for Porosity in Gold and PalladiumCoatings by Sulfurous Acid/Sulfur-Dioxide VaporB 809 Test Method for Porosity in Metallic Coatings byHumid Sulfur Vapor (“Flowers-of-Sulfur”)B 866 Test Method for Gross Defects and MechanicalDamage in Metallic Coatings by Polysulfid
10、e Immersion3. Terminology3.1 DefinitionsMany terms in this test method are definedin Terminology B 374 or B 542.3.2 Definitions of Terms Specific to This Standard:3.2.1 base metal, nany metal other than gold, silver,platinum, palladium, iridium, or rhodium. Typical base metalsused as underplates or
11、substrates are copper, nickel, tin, lead,and their alloys.3.2.2 defect indications, ncolored droplets resulting fromthe reaction between the PMA reagent and the underlyingmetal.3.2.3 gross defects, nthose breaks in the coating thatexpose relatively large areas of underlying metal to theenvironment.
12、Gross defects include those produced by me-chanical damage and wear, as well as as-plated large pores withdiameters an order of magnitude greater than intrinsic porosityand networks of microcracks.NOTE 1Large pores and microcrack networks indicate serious devia-tions from acceptable coating practice
13、 (dirty substrates and contaminatedor out-of-balance plating baths).3.2.4 intrinsic porosity, nthe normal porosity that ispresent, to some degree, in all commercial thin electrodeposits1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direc
14、t responsibility of Subcommittee B08.10 onTest Methods.Current edition approved Aug. 1, 2008. Published September 2008. Originallyapproved in 1996. Last previous edition approved in 2003 as B 877 96 (2003).2Clarke, M., “Porosity and Porosity Tests,” Properties of Electrodeposits, ed. bySand, Leidhei
15、ser, and Ogburn, The Electrochemical Society, 1975, p. 122.3Krumbein, S. J., “Porosity Testing of Contact Platings,” Trans. Connectors andInterconnection Technology Symposium, Philadelphia, PA, October 1987, p. 47.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM C
16、ustomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.5Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.(precious metal coati
17、ngs for engineering purposes) that willgenerally follow an inverse relationship with thickness.NOTE 2Intrinsic porosity is due to small deviations from ideal platingand surface preparation conditions. Scanning electron microscope (SEM)studies have shown the diameter of such pores at the plating surf
18、ace is 1to 2 m so only small areas of underlying metal are exposed to theenvironment.3.2.5 measurement area, nthat portion or portions of thesurface that is examined for the presence of gross defects ormechanical damage and wear through. The measurement areashall be indicated on the drawings of the
19、parts or by theprovision of suitably marked samples.3.2.6 metallic coatings, ninclude electrodeposits, clad-dings, or other metallic layers applied to the substrate. Thecoating can comprise a single metallic layer or a combinationof metallic layers (gold over palladium).3.2.7 porosity (general), nth
20、e presence of any hole, crack,or other defect that exposes the underlying metal to theenvironment.3.2.8 underplate, na metallic coating layer between thesubstrate and the topmost metallic coating. The thickness of anunderplate is usually greater than 1 m, in contrast to a strikeor flash, which is us
21、ually thinner.3.2.9 wear through, nthe exposure of underplate or sub-strate as a direct result of wear. Wear through is an observablephenomenon.3.2.10 wear track, na mark that indicates the path alongwhich physical contact has been made during a sliding process(the mating and unmating of an electric
22、al contact).4. Summary of Test Method4.1 This test method involves the use of a solution ofphosphomolybdic acid (PMA), which is a solid complex ofmolybdenum trioxide, Mo2O3, and phosphoric acid, H3PO4.Inthis state, molybdenum is very reactive with many free metalsand may be used to detect exposed un
23、derplates and substratemetals. The part is exposed briefly to fumes of hydrochloricacid to remove oxides in the defect region. A small drop of theaqueous PMA solution is applied to the spot in question usingan applicator. If it contacts base metals from exposed under-plate or substrate, the Mo2O3wil
24、l immediately be reduced tolower oxides, forming the intensely colored, molybdenum bluecomplex (heteropoly blue).64.2 This test may not be suitable for some precious metalalloy coatings that contain significant concentrations of non-precious metals (base metals) like nickel or copper. (See .)4.3 The
25、 reagents in this test also react with tin, lead, andtin-lead solder.5. Significance and Use5.1 The primary purpose of the PMAtest is to determine thepresence of mechanical damage, wear through, and other grossdefects in the coating. Most metallic coatings are intended tobe protective, and the prese
26、nce of gross defects indicates aserious reduction of such protection.5.2 The protection afforded by well applied coatings may bediminished by improper handling following plating or as aresult of wear or mechanical damage during testing or while inservice. The PMA test can serve to indicate the exist
27、ence ofsuch damage.5.3 This test is used to detect underplate and substrate metalexposed through normal wear during relative motions (matingof electrical contacts) or through mechanical damage. As such,it is a sensitive pass/fail test and, if properly performed, willrapidly detect wear through to ba
28、se metals or scratches thatenter the base metal layers.5.4 This test is relatively insensitive to small pores. It is notdesigned to be a general porosity test and shall not be used assuch. The detection of pores will depend upon their sizes andthe length of time that the reagent remains a liquid.5.5
29、 This test cannot distinguish degrees of wear through orwhether the wear through is to nickel or copper. Once basemetal is exposed, the colored molybdenum complex is formed.While relatively small area defects (compared to the area of thedroplet) may be seen at the bottom of the drop as tiny coloredr
30、egions immediately after applying the PMA, any larger areasof exposed base metal will cause the entire droplet to turn darkinstantly.5.6 The PMA test also detects mechanical damage thatexposes underplate and substrate metal. Such damage mayoccur in any postplating operation or even at the end of the
31、plating operation. It can often occur in assembly operationswhere plated parts are assembled into larger units by mechani-cal equipment.5.7 The PMA test identifies the locations of exposed basemetal. The extent and location of these exposed areas may ormay not be detrimental to performance. The PMA
32、test is notrecommended for predictions of product performance, nor is itintended to simulate field failure mechanisms. For such contactperformance evaluations, an environmental test known tosimulate actual failure mechanisms should be used.5.8 The PMA test is primarily intended for the evaluation of
33、individual samples rather than large sample lots, since evalu-ations are normally carried out one at a time under themicroscope (see Section 10).5.9 This test is destructive. Any parts exposed to the PMAtest shall not be placed in service.6. Apparatus6.1 In addition to the normal equipment (beakers,
34、 weighingbalances, funnels, etc.) that are a part of every chemicallaboratory.6.2 Microscope, Optical, Stereo, 10 to 303It is preferredthat one eyepiece contain a graduated reticle for measuring thedefect location. The reticle shall be calibrated for the magni-fication at which the microscope is to
35、be used, preferably103.76.3 Light source (illuminator) for microscope, incandescent.6.4 Glass volumetric flask, 10 mL.6Van Wazer, J. P., Phosphorous and Its Compounds, Interscience Publishers,New York, 1961.7Magnification standards suitable for calibrating optical microscopes may bepurchased from U.
36、S. National Institute of Standards and Technology, Office ofStandard Reference Materials.B 877 96 (2008)26.5 Glass bottle of a stable shape and with glass stopper. Thebottle opening shall be 2.5 cm (1 in) minimum. An example isa 50-mL low-form weighing bottle or a flask-shaped weighingbottle.6.6 App
37、licators (see 9.2)Platinum wire, 32 AWG, ordisposable glass micropipets, 1 or 0.5 L size.7. Reagents and Materials7.1 Phosphomolybdic Acid (PMA)Crystalline, ACS certi-fied grade.7.2 Concentrated Hydrochloric Acid ACS analytical re-agent (AR) grade or better.8. Specific Safety and Health Precautions8
38、.1 All the normal precautions shall be observed in handlingthe materials required for this test. This shall include, but is notlimited to, procuring and reviewing Material Safety DataSheets that meet the minimum requirements of the OSHAHazard Communication Standard for all chemicals used incleaning
39、and testing and observing the recommendationsgiven.9. Preparations9.1 Preparation of solutions:9.1.1 Two types of PMA solutions can be used with thismethod.9.1.1.1 Method A, the preferred method, uses a dilute 8 %solution of PMA in water.9.1.1.2 Method B, uses a saturated solution of PMA inwater.NOT
40、E 3The dilute solution is preferred because it works well withsilver, gold, and palladium coatings, while the saturated solution reactswith silver to give false indications. In addition, the saturated solution hasa tendency to dry up quickly on the test surface before proper evaluationscan be made.9
41、.1.2 Dilute (8 %) PMA solution (for Method A):9.1.2.1 Place a small, clean, and dry glass funnel in the neckof a clean, dry 10 mL volumetric flask.9.1.2.2 Tare out the weight of the funnel and flask on abalance.9.1.2.3 Weigh 0.8 (60.1) g PMA into the flask, using aplastic or glass spatula.9.1.2.4 Ri
42、nse the funnel with distilled or deionized water todrain 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. Cloudysolution will clear after standing 10 to 15 min.9.1.2.7 Pour clear solution into a clean glass bottle and seal
43、with glass stopper. Label bottle with PMA concentration anddate of preparation.9.1.2.8 Store bottle in refrigerator. Solution may be used forone week.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,except use approximately5gofPMAinstead of 0.8
44、g. (Filterout sediment, if necessary.)9.1.3.2 Mix thoroughly for at least 10 min.NOTE 4There shall be a small excess of PMA, seen as a sediment inthe bottom of the flask. This indicates saturation.9.1.3.3 Pour into a clean bottle and label bottle withcontents and preparation date.9.1.3.4 Solution ma
45、y be used for one week. Store inrefrigerator when not in use.9.1.4 Hydrochloric acid (for both methods):9.1.4.1 Fill the special glass bottle (see 6.4) to approxi-mately halfway from the top.9.1.4.2 Label glass bottle with contents.9.1.4.3 Keep stoppered and under a fume hood when not inuse.9.2 Prep
46、aration of applicators:9.2.1 The applicator shall not react with the PMA solution.Examples are as follows:9.2.1.1 PlatinumMake a small loop using a 32 AWGplatinum wire and an appropriate size mandrel (such as aneedle). Leave a small gap to facilitate release of the PMAdroplet (see Fig. 1). Attach lo
47、op to a wooden or plastic handle.9.2.1.2 Platinum inoculating loops with handles may bepurchased. Cut the loop with a knife to create a small gap (Fig.1), which will facilitate the release of the PMA droplet.9.2.1.3 Glass capillary micropipets in the 1-L size orsmaller.9.2.2 If a platinum loop is us
48、ed as the applicator, the loopdiameter shall preferably be 1 mm and shall not exceed 2 mm.The loop diameter is kept small for the following reasons:9.2.2.1 The small dimensions of many examination areas.9.2.2.2 The ability of the loop to release a rounded dropletinstead of a thin sheet of solution,
49、which dries too fast.9.2.2.3 Difficulty in controlling flow and observing reac-tions in large drops.9.3 Preparation of test samples:9.3.1 Handle samples as little as possible even prior tocleaning and only with tweezers, microscope-lens tissue, orclean, soft cotton gloves.9.3.2 Prior to being cleaned, the samples shall be preparedso the measurement area is accessible and can be placed in abasically horizontal plane. This allows for easy viewingthrough the microscope and prevents the PMA solution fromrunning off during application.9.3.3 Masking:9.3.3.1 The PMA
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