Tin

Tinning is a collective term for various surface finishing processes . By the tin plating is a tin coating on most metallic articles produced. Although tin is a relatively good corrosion has resistance that is corrosion protection is not the main reason to choose this metal as a coating material - the most important properties of tin coatings are made in food safety and the solderability .

Objects that are tinned are mostly made of steel , copper or copper alloys . Zinc die-cast , other metals or alloys and plastic are less commonly tinned.

Hot-dip tinning

In this process, the objects to be tinned are immersed in a molten tin bath after a suitable pretreatment ( hot dip ). When the objects are lifted out of the tin bath, the tin adheres to the surface and a solid tin coating forms on cooling. This process was already known in antiquity and many hobbyists today know the tinning of a copper wire with a soldering iron and solder. In modern times hot-dip tinning was used on a large scale to produce tinplate (tinned steel sheet). With the advent of electroplating technology , hot-dip tinplate fell sharply in favor of electroplated tinplate.

When tinning copper strips and contacts, hot-dip tinning was able to defend its position compared to electroplating in some areas. A major advantage of hot-dip tinning of copper is the formation of alloy layers at the boundary between the base metal and the coating - these alloy layers lead to extremely good adhesion of the coating.

Galvanic tinning

In galvanic tinning, the objects to be tinned are immersed in a tin electrolyte after a suitable pretreatment . When an electrical voltage is applied, a tin coating is deposited on the surface of the objects. With this method, very thin layers of a few µm can also be produced, which means that the material consumption is correspondingly low. This process therefore has economic advantages over hot-dip tinning. Electroplating has become very important for the food industry (tinplate) and for the electrical and electronics industry (copper contacts, copper strips, electronic components).

Tin coatings can produce a dreaded and exotic appearance: under certain conditions, fibers grow from the tin coating. These whiskers, which are up to 100 µm long, pose a major threat to highly miniaturized electronic components and circuits.

In the past, tin-lead alloys were often used because of their lower tendency towards whiskers. Since the RoHS, there has been the challenge of producing whisker-proof tin coatings without lead ( using suitable additives and process parameters).

Reflow process

This process is a combination of galvanic tinning and a subsequent heat treatment up to above the melting point of the tin. An attempt is made to combine the advantages of galvanic and hot-dip tinning: thin layers and the formation of alloy layers.

Chemical tinning

By immersing copper plates in a solution of a tin salt such as tin sulfate , sulfuric acid and thiourea as well as brighteners and wetting agents , chemical (electroless) tinning of copper surfaces is possible. Due to the simplicity of the process, this is interesting for the home sector for tinning blanks, among other things. The tin layer applied in this way is very smooth and has a thickness in the µm range. Due to its small thickness, however, the tin transforms into a copper-tin phase or copper-tin alloy during long storage through the diffusion of copper .

Areas of application

In the packaging industry (tinplate), electrical engineering , electronics as well as in roof plumbing and body construction , also with homogeneous lead in chemical apparatus engineering and cable technology.

See also

• soldering
• Galvanizing

Individual evidence

1. ^ Brockhaus ABC chemistry. VEB FA Brockhaus Verlag, Leipzig 1965, p. 1484.
2. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 6: T-Z. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1988, ISBN 3-440-04516-1 , p. 4507.
3. ^ Gerhard Jokisch, Bruno Schütze, Werner Städtler in: Author collective: The basic knowledge of the engineer. VEB Fachbuchverlag, Leipzig 1968, pp. 991–1163, there p. 1048.
4. ↑ ^{a b} Microcirtec brochure ( Memento of the original from July 15, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF file; 396 kB). 

literature

• On the history of tinning ( white boiling process , fat tinning , electrolytic tinning , tin disease ): Julius Grünwald: Treatises from iron enamel and tinning technology: collected technological-historical work , Leipzig-R. 1910, pp. 158-207.