Process description: Plating tin and alloy
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- Tin and alloy plating
Tin plated metal is widely used in many applications because of its unique properties. Plated tin coatings are non-toxic, ductile, resistant to corrosion, easy to coat, and have high throwing and good distribution properties. This makes it possible to plate items with complex shapes to a uniform thickness compared with hot tin dipping methods. Tin finishes are also subsequently easier to solder components onto.
The main applications of tin are the coating of steel coil for packaging of food, beverages and aerosols, etc. It is also widely used in printed circuit boards, electronic components, appliance chassis, as well as for kitchen utensils.
Several different electrolytes are available, such as acid stannous sulphate, acid tin fluoroborate, alkaline sodium or potassium stannate and more recently the stannous systems based on organic acids, such as methane sulphonic acid, (MAS) and accounts for 13% of Europe tin plate production. The simpler sulphate baths containing stannous sulphate, sulphuric acid and addition agents (antioxidants for stannous tin, plus grain refiner) are the most popular in rack and barrel applications because of their high current efficiency.
Tin lead plating is the most commonly tin plated alloy. It is used as solder coat in different alloy ratios (60/40, 90/10, 95/5) traditionally using stannous, and lead fluoroborates with fluoroboric acid and additives.
Non-fluoroboric tin lead electrolytes are now available based on the organic methane sulphonate acid. They have improved stability, low sludge formation, higher plating rates, better deposit properties and structure of the deposit. They are widely-used in reel- to-reel machines, as well as in barrel processing.
Tin-nickel has high throwing power, good distribution of metal, ductile, non-toxic, and is readily soldered to.
Source: BAT Surface Treatment of Metals and Plastic, Aug. 2006.
