ASTM B545-13 pdf free download.Standard Specification for Electrodeposited Coatings of Tin.
1.1This specification covers the requirements for electrode- posited (electroplated) coatings of tin applied to metallic articles. Tin coatings are used to provide a low contact- resistance surface, to protect against corrosion (see I .2), to facilitate soldering, to provide anti-galling properties, and to be a stopoff coating in the nitriding of high-strength steels.
1.2 Some corrosion can be expected from tin coatings exposed outdoors. In normal indoor exposure. tin is protective on iron, steel, nickel. copper. and their alloys. Corrosion can he expected at discontinuities in the coating (such as pores) due to galvanic couples formed between the tin and the underlying metal through the discontinuities. especially in humid atmospheres. Porosity increases as the coating thickness decreases, so that minimum thicknesses must be specified for each application. Parts coated with tin can be assembled safely in contact with iron and steel, tin-coated aluminum, yellow chrornated zinc, cadmium, and solder coatings. (See X5.l for oxidation and corrosion properties.)
1 .3 This specification applies to electroplated coatings of not less than 99 % tin (except where deliberately alloyed for special purposes. as stated in X6.3) obtained from any of the available tin electroplating processes (see 4.3).
1.4 This specification does not apply to hot-dipped tin or other non-electrodeposited coating: it also does not apply to mill products. For mill products, refer to Specifications A623 or A623M.
1.5 The values stated in SI units are to he regarded as the standard. The values given in parentheses are for information only.
3. Terminology
3.1 Definitions:
3.1.1 Many of the terms used in this specification are defined in Terminology B374 or B542.
3.1.2 rack-plating—an electrodeposition process in which articles to be coated are mounted on racks or other fixtures during the process.
3.1.3 significant surface—that portion of the surface of a coated article at which the coating is required to meet all of the requirements of the coating specification for that article; significant surfaces are usually those that arc essential to the serviceability or function of the article, or that can be a source of corrosion products or tarnish films that interfere with the function or desirable appearance of the article; significant surfaces shall be indicated on the drawings of the parts or by the provision of suitably marked samples.
3. 1 .4 undercoating (see 3. 1.5)—also called an underplate in the electronics industry.
3.1 .5 underplaring—application of a metallic coating layer between the basis metal or substrate and the topmost metallic coating or coatings. The thickness of such an undercoating is usually greater than 0.8 pm (30 pin.). This is in contrast to strikes or flashes, whose thicknesses are generally much smaller.
4. Classification
4.1 General—Orders for articles to be plated in accordance with this specification shall specify the service class (4.2) (and underplating, if required), indicating the severity of service required for the coating. Other coatings variations, such as surface appearance type (4.3) or alloy composition (Appendix X6), are optional.ASTM B545 pdf download.