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Besides manufacturing contact materials from the solid phase, i.e. by melt or powder metallurgy, the production starting in the liquid or gaseous phase is generally preferred when thin layers within the μm range are required , which cannot be obtained economically by conventional cladding methods (<xr id="tab:Overview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications"/><!--(Tab. 7.1)-->). Such coatings fulfill different requirements depending on their composition and thickness.
They can serve as corrosion or wear protection or can fulfill the need for thin contact layers for certain technical applications. In addition they serve for decorative purposes as a pleasing and wear resistant surface coating.
For electroplating of metals, especially precious metals, water based solutions (electrolytes) are used, which contain the metals to be deposited as ions (i.e. dissolved metal salts). An electric field between the anode and the work pieces as the cathode, forces the positively charged metal ions to move to the cathode where they give up their charge and deposit themselves as metal on the surface of the work piece.
Depending on the application, for electric and electronic or decorative end use, different electrolytic bath solutions (electrolytes) are used. The electroplating equipment used for precious metal plating and its complexity varies widely, depending on the process technologies employed.
Electroplating processes are encompassing, besides the pure metal deposition, also preparative and post treatments of the goods to be coated. An important parameter for creating strongly adhering deposits is, that the surface of the goods has to be metallic clean without oily or oxide film residues. This is achieved through various pre-treatment processes, specifically developed for the types of material and surface conditions of the goods to be plated.
In the following segments, electrolytes – both precious and non-precious – as well as the most widely used electroplating processes are described.
Coatings produced by PVD processes are used for contact applications, for example on miniature-profiles, in electrical engineering and for electronic components, for solderability in joining processes, for metalizing of nonconductive materials, as well as in semiconductors, opto-electronics, optics and medical technology applications.
There are few limitations regarding the geometrical shape of substrate parts. Only the interior coating of drilled holes and small diameter tubing can be more problematic (ratio of depth to diameter should be < 2:1). Profile wires, strips and foils can be coated from one side or both; formed parts can be coated selectively by using masking fixtures that at the same time serve as holding fixtures (<xr id="fig:Examples of vacuum coated semi finished materials and parts"/>).
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==<!--7.3-->Comparison of Deposition Processes==
The individual deposition processes have in part different performance characteristics. For each end application, the optimal process has to be chosen, considering all technical and economical factors. The main selection criteria should be based on the electrical and mechanical requirements for the contact layer and on the design characteristics of the contact component. (<xr id="tab:Comparison of different coating processes"/><!--Table 7.7-->) gives some indications for a comparative evaluation of the different coating processes.
The electroless metal coating is not covered here because of the low thickness of deposits, which makes them in most cases not suitable for contact
The properties of these reflow tin coatings are comparable to those created by conventional hot tinning.
Besides overall tin coating of strip material, the hot tinning can also be applied in the form of single or multiple stripes on both sides of a continuous substrate strip(<xr id="fig:Typical examples of hot tinned strip materials"/>).
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*'''Materials'''
Solid lubricants include for example 0.05 – 0.2 μm thin hard gold layers, which are added as surface layers on top of the actual contact material.
Among the various contact lubricants offered on the market, contact lubrication oils have shown performance advantages. They are mostly synthetic, chemically inert and silicone-free oils such as for example the DODUCONTA contact lubricants which differ in their chemical composition and viscosity.
For sliding contact systems with contact forces < 50 cN and higher sliding speeds, oils with a lower viscosity (< 50 mPa·s) are preferential. For applications with higher contact forces and operating at higher temperatures, contact oils with a higher viscosity are advantageous. Contact oils are mainly suited for applications at low current loads. At higher loads and in situations where contact separation occurs during the sliding operation, thermal decomposition may be initiated, which causes the lubricating properties to be lost.
==<!--7.6-->Passivation of Silver Surfaces==
The formation of silver sulfide during the shelf life of components with silver surface in sulfur containing environments, can be significantly eliminated by coating them with an additional protective film layer (Passivation layer). For electrical contact use, such thin layers should be chemically inert and sufficiently conductive, otherwise they are easily broken by the applied contact force.
<figure id="fig:Typical process flow for the SILVERBRITE W ATPS process">
[[File:Typical process flow for the SILVERBRITE W ATPS process.jpg|right|thumb|Figure 4: Typical process flow for the SILVERBRITE W ATPS process]]
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The passivation process SILVERBRITE W ATPS is a water-based tarnish preventer for silver (<xr id="fig:Typical process flow for the SILVERBRITE W ATPS process"/>). It is free of chromium(VI) compounds and solvents. The passivating layer is applied by immersion, which creates a transparent organic protective film which barely changes the appearance and only slightly
increases the good electrical properties such as for example the contact resistance. The good solderability and bond properties of silver are not
negatively affected. Because of its chemical composition, this protective layer has some lubricating properties which reduce the insertion and withdrawal forces of connectors noticeably.
==References==
