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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 importantparameter for creating strongly adhering deposits is the surface of the goods 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.
Electroless plating is defined as a coating process which is performed without the use of an external current source. It allows a uniform metal coatingindependent of the geometrical shape of the parts to be coated. Because of the very good dispersion capability of the used electrolytes also cavities and the inside of drilled holes in parts can be coated for example.
In principal two different mechanisms are employed for electroless plating: processes in which the carrier material serves as a reduction agent (Immersion processes) and those in which a reduction agent is added to the electrolyte (Electroless processes).
[[File:Principle of sputtering.jpg|right|thumb|Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms]]
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Initially a gas discharge is ignited in a low pressure (10<sup>-1</sup> -1 Pa) argon atmosphere. The argon ions generated are accelerated in an electric field andimpact the target of material to be deposited with high energy. Caused by this energy atoms are released from the target material which condensate on theoppositely arranged anode (the substrate) and form a layer with high adhesion strength. Through an overlapping magnetic field at the target location thedeposition rate can be increased, making the process more economical.
The advantages of the PVD processes and especially sputtering for electrical contact applications are:
*Excellent adhesion (also by using additional intermediate layers)
Coatings produced by PVD processes are used for contact applications, for example on miniature-profiles, in electrical engineering and for electroniccomponents, 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.