Changes

During hot-dip tinning pre-treated strip materials are coated with pure tin or tinalloys from a liquid solder metal. During overall (or all-around) tinning thestripsthrough a liquid metal melt. For strip tinning rotating rolls are partiallyimmersed into a liquid tin melt and transport the liquid onto the strip which isguided above them. Through special wiping and gas blowing procedures thedeposited tin layer can be held within tight tolerances. Hot tinning is performeddirectly onto the base substrate material without any pre-coating with eithercopper or nickel. Special cast-on processes or the melting of solder foils ontothe carrier strip allow also the production of thicker solder layers(> 15 μm).

The main advantage of hot tinning of copper and copper alloys as compared totin electroplating is the formation of an inter-metallic copper-tin phase (Cu₃Sn,Cu₆ Sn₅) at the boundary between the carrier material and the tin layer. This thin(0.3 – 0.5 μm) intermediate layer, which is formed during the thermal tinningprocess, is rather hard and reduces in connectors the frictional force andmechanical wear. Tin coatings produced by hot tinning have a good adhesion tothe substrate material and do not tend to tin whisker formation.

A special process of hot tinning is the “Reflow” process. After depositing a tincoating by electroplating the layer is short-time melted in a continuous process.The properties of these reflow tin coatings are comparable to those created byconventional hot tinning.

Besides overall tin coating of strip material the hot tinning can also be applied inthe form of single or multiple stripes on both sides of a continuous substratestrip.

Mechanical strength and dimensional tolerances of hot tinned strips are closelyrelated to the standard for Cu and Cu alloy strips according to DIN EN 1652 andDIN EN 1654.

By using suitable lubricants the mechanical wear and frictional oxidation ofsliding and connector contacts can be substantially reduced. In the electricalcontact technology solid, as well as high and low viscosity liquid lubricants areused.

Solid lubricants include for example 0.05 – 0.2 μm thin hard gold layers whichare added as surface layers on top of the actual contact material.

Among the various contact lubricants offered on the market contact lubricationoils have shown performance advantages. They are mostly synthetic, chemically inert, and silicone-free oils such as for example the DODUCONTAcontact lubricants which differ in their chemical composition and viscosity.

For sliding contact systems with contact forces < 50 cN and higher slidingspeeds oils with a lower viscosity (<50 mPa·s) are preferential. For applicationswith higher contact forces and operating at higher temperatures contact oilswith a higher viscosity are advantageous. Contact oils are mainly suited forapplications at low current loads. At higher loads and in situations wherecontact separation occurs during the sliding operation thermal decompositionmay be initiated which causes the lubricating properties to be lost.

Most compatible with plastics are the contact oil varieties B5, B12K, and B25,which also over longer operating times do not lead to tension stress corrosion.

For the optimum lubrication only a very thin layer of contact oil is required.Therefore it is for example recommended to dilute the oil in iso-propylenealcoholduring the application to contact parts. After evaporation of the alcohola thin and uniform layer of lubricant is retained on the contact surfaces.

The formation of silver sulfide during the shelf life of components with silversurface in sulfur containing environments can be significantly eliminated bycoating them with an additional protective film layer (Passivation layer). Forelectrical contact use such thin layers should be chemically inert andsufficiently conductive, or be easily broken by the applied contact force.

The passivation process SILVERBRITE W ATPS is a water-based tarnishpreventer for silver. It is free of chromium(VI) compounds and solvents. Thepassivating layer is applied by immersion which creates a transparent organicprotective film which barely changes the appearance and only slightlyincreases the good electrical properties such as for example the contactresistance. The good solderability and bond properties of silver are notnegatively affected. Because of its chemical composition this protective layerhas some lubricating properties which reduce the insertion and withdrawal