5.1 The purpose of the alkaline polysulfide immersion 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 alkaline polysulfide test serves to indicate if the damage has extended down to the copper or copper alloy basis metal since it will not detect exposed nickel underplate.

5.3 The alkaline polysulfide test has been specified in several ASTM specifications for tin-plated coatings, namely Specifications B246 and B545. This test could also be used to detect gross defects and mechanical damage in other metallic coatings, such as tin-nickel alloy (Specification B605), nickel (Specification B689), gold (Specification B488), palladium (Specification B679), and autocatalytic nickel-phosphorous coatings (Specification B733).

5.4 This test detects mechanical damage that exposes copper underplate and copper basis metal. Such damage may occur in any post-plating operation or even towards the end of the plating operation. It is most often seen to occur in product assembly operations.

5.5 If properly performed, this test will also detect wear-through, provided the wear-through reaches a copper or copper-alloy layer.

5.6 Many types of gross defects are too small to be seen, except at magnifications so high (as in SEM) that a realistic assessment of the measurement area cannot be easily made. Other defects, such as many types of wear-through, provide insufficient contrast with the coating surface. Gross defects tests (as with porosity tests) are, therefore, used to magnify the defect sites by producing visible reaction products in and around the defects.

5.7 The polysulfide solution will react with copper and copper alloys to produce a dark brown or black stain (the defect indications) at the site of the defect. Silver also turns black under the same conditions. The test solution will not react with nickel and is only useful when the presence or absence of copper exposure is a specific requirement.

5.8 The polysulfide immersion test is relatively insensitive to the presence of small pores. It shall not be used as a general porosity test. (Test Method B809 should be used instead.)

5.9 The extent and location of the gross defects or mechanical damage (revealed by this test) may or may not be detrimental to product performance or service life. Such determinations shall be made by the user of the test through practical experience or judgment.

5.10 The present test can be used on samples of various geometries, such as curved surfaces. It can also be used for selective area coating if allowance is made for tarnish creepage from bare copper alloy areas.

5.11 This test is destructive in that it reveals the presence of gross defects by contaminating the surface with reaction-product films. Any parts exposed to this test shall not be placed in service.

5.12 However, the defect indications on the sample surfaces that result from this test are stable; samples may be retained for reference purposes.

5.13 This test is neither recommended for predictions of product performance nor is it intended to simulate field failure mechanisms. For such product performance evaluations, an environmental test that is known to simulate actual failure mechanisms should be used.