【国外标准】 Standard Test Method for Gross Defects and Mechanical Damage in Metallic Coatings by the Phosphomolybdic Acid (PMA) Method

5.1 The primary purpose of the PMA test is to determine the presence of mechanical damage, wear through, and other gross defects in the coating. Most metallic coatings are intended to be protective, and the presence of gross defects indicates a serious reduction of such protection.5.2 The protection afforded by well applied coatings may be diminished by improper handling following plating or as a result of wear or mechanical damage during testing or while in service. The PMA test can serve to indicate the existence of such damage.5.3 This test is used to detect underplate and substrate metal exposed through normal wear during relative motions (mating of electrical contacts) or through mechanical damage. As such, it is a sensitive pass/fail test and, if properly performed, will rapidly detect wear through to base metals or scratches that enter the base metal layers.5.4 This test is relatively insensitive to small pores. It is not designed to be a general porosity test and shall not be used as such. The detection of pores will depend upon their sizes and the length of time that the reagent remains a liquid.5.5 This test cannot distinguish degrees of wear through or whether the wear through is to nickel or copper. Once base metal is exposed, the colored molybdenum complex is formed. While relatively small area defects (compared to the area of the droplet) may be seen at the bottom of the drop as tiny colored regions immediately after applying the PMA, any larger areas of exposed base metal will cause the entire droplet to turn dark instantly.5.6 The PMA test also detects mechanical damage that exposes underplate and substrate metal. Such damage may occur in any postplating operation or even at the end of the plating operation. It can often occur in assembly operations where plated parts are assembled into larger units by mechanical equipment.5.7 The PMA test identifies the locations of exposed base metal. The extent and location of these exposed areas may or may not be detrimental to performance. The PMA test is not recommended for predictions of product performance, nor is it intended to simulate field failure mechanisms. For such contact performance evaluations, an environmental test known to simulate actual failure mechanisms should be used.5.8 The PMA test is primarily intended for the evaluation of individual samples rather than large sample lots, since evaluations are normally carried out one at a time under the microscope (see Section 10).5.9 This test is destructive. Any parts exposed to the PMA test shall not be placed in service.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 literature.2, 3 An ASTM guide to the selection of porosity and gross defect tests for electrodeposits and related metallic coatings is available as Guide B765. Other related porosity and gross defects test standards are Test Methods B735, B741, B798, B799, B809, and B866, Specifications B488, B679,and B689.1.3 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.