Electroplated tin

Because of the ease with which they can be soldered, electroplated tin—lead coatings of near eutectic composition (62 wt % tin) are extensively used in the electronics industry for coating printed circuit boards and electrical coimectors, lead wires, capacitor and condenser cases, and chassis. 

General thickness requirements for electroplated tin coatings on ferrous and non-ferrous substrates are contained in BS 1872 1984 and ISO 2093 and these are essentially the same as those in Tables 13.12 and 13.13. 

Tin, as well as some other metals, can undergo a phenomenon where tiny metal filaments, called whiskers, form randomly on parts used in electrical applications. In low voltage, miniature circuitry, whiskers can cause short circuits. Alloys having 2% lead minimum or 0.5% bismuth or heat treatments are said to overcome the problem. A specification for electroplated tin coatings is available (133). 

Use Water analysis, laboratory reagent, electroplated tin coating baths, manufacture of intermediates and dyes, pharmaceuticals. 

Electroplated tin, which in contrast to hot dipped tin, mostly looks matte or semilustrous, but can be brightened by reflowing, that is heating for a short time (some seconds up to a minute) above the melting point of tin (232 °C). Table 10 summarizes the composition and working parameters of the commonly used tin electrolytes. 

Uses Water analysis laboratory reagent electroplated tin coating baths mfg. of intermediates, dyes, and pharmaceuticals catalyst for foundry resins descaling agent curing aid for plastics hydrotrope Manuf./Distrib. Aldrich Alfa Chem Kira Spectrum Quality Prods. 

Uses Electroplated tin coating baths intermediate in mfg. of dyes and pharmaceuticals reagent for colored aluminum anodizing Manuf./Distrib. Aldrich Fluka Kishida Chem. Sloss Ind. 

Electroplated tin—Electroplated Sn exhibits excellent solderability and corrosion resistance, but is prone to Sn whisker growth. Thin, hairlike whiskers grow from the surface and pose as a potential reliability problem due to electrical shorts caused in the field. Heat fusing or reflow is used to eliminate tin whiskers [53]. 

Electroplated Sn is another finish for both boards and components that is rapidly becoming a leading candidate. Electroplated tin can be deposited with a variety of deposit appearances and characteristics as noted in Table 13. 

Much additional information on electroplated tin deposits is provided in Section 4 on component finishes. 

TABLE 13 Characteristics of Various Types of Electroplated Tin (Sn) Finishes for Both Boards and Component Leads... 

Tin whiskers are thin single crystal filaments that grow from electroplated tin and tin-rich coatings after plating. The propensity of tin or tin-based coatings to spontaneously form whiskers is well documented and has been known for some time [13,14]. Tin whiskers appear in many different physical shapes and sizes, as shown in Fig. 19. Much has been written on this subject as it is of great concern within the electronics industry as tin whiskers have been known to cause short-circuit field failures in commercial and military electronic products. Pure tin is not the only candidate to possess a tin whisker risk, and in fact all Sn-rich Sn alloys including Sn-Bi, Sn-Ag, Sn Cu, and especially Sn Zn pose reliability risks from the threat of tin whiskers. 

Moon, K.W., et al. The Formation of Whiskers on Electroplated Tin Containing Copper, Proceedings of 4th Pacific Rim Conference on Advanced Materials and Processing Honolulu, Hawaii, Dec. 2001 4 pp. 

Kakeshita, T. Shimizu, K. Kawanaka, R. Hasegawa, T. Grain size effect on electroplated tin coatings on whisker growth. J. Mater. Sci. 1982, 17, 2560-2566. 

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