Hot-dip tinned copper and copper alloy strip

Hot-dip tinned strip Characteristic for hot-dip tinned coatings is the formation of intermetallic phases (IMP) between the base material and the tin layer, see Fig. 2. They consist of Cu3Sn and Cu6Sn5. The intermetallic phase produced in this way ensures a very good bonding of the tin layer to the base material as well as a high degree of protection against whisker formation. Strip with a well-cleaned and activated surface is given through the molten tin bath, see Fig. 1. After leaving the tin bath, the coating is still liquid and adheres to the strip. The liquid tin is blown by an air stream...

HDT coating types Fig. 2 shows the different types of hot-dip tin coatings which are: . – SnPUR® : Pure tin – SnTEM® : Thermal tin 100 % intermetallic phase (IMP) SnPUR®: These hot-dip tin coatings have a low hardness and therefore are very ductile. SnPUR® coatings ensure a low contact resistance between the mating partners as well as a good solderability. SnTEM®: The tin layer is transformed by a subsequent heat treatment into a very hard and brittle CuSn intermetallic compound. The friction coefficient of this CuSn surface is significantly lower than that of tin. This advantage is used in multipole...

Copper and copper alloy strips with hot-dip tinning layers are standardized in DIN EN 13148. This standard describes the following characteristics: - Nature of the coating: In order to avoid surface defects caused by transport (e. g. fretting corrosion), the strip may have a lubricating film on the surface. - Appearance of the coating: As a consequence of using liquid tin there are visible crystallisation phenomena which, however, have no influence on the contact properties of the coating. - Solderability: The soldering properties are essentially dependent on the type of coating and the thickness...

Funcional properties - Low contact resistance, and thus an excellent electrical connection is achieved by optimally embedding the mating partner in the free pure tin. - High whisker resistance, as the hot-dip tinning forms its IMP with low stress at high temperatures. - Good corrosion resistance due to a passivating, stable natural tin oxide and the absence of pores. - Low mating forces, achieved on the one hand by using thin coating thicknesses with a low proportion of pure tin and on the other hand by high surface hardness through the use of SnTEM® - Good wear resistance in multiple mating...

Dimensions and edge designs Dimensions Hot-dip tinned coatings can be applied to strip thicknesses from 0.1 to 2.0 mm and strip widths up to almost 400 mm. Detailed information is given in Fig. 5. Strip thicknesses of > 1.6 mm are considered to be “difficult for hot-dip tinning” for certain base materials. For this reason, the feasibility must be confirmed before placing the order. Standard design: Strip edges are uncoated. Special design: tinned strip edges, dimensions available on request. Edge designs Traverse wound coils Strip thickness (mm) Fig. 4: Ranges of available dimensions for hot-dip...

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