Changes

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 in 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 ApplicationsOverview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications"/> <!--(Tab. 7.1)-->). Such coatings fulfill different requirements depending on their composition and thickness.

<figtable id="tab:Overview of Important Properties of Electroplated Coatings and their ApplicationsOverview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications"><caption>'''<!--Table 7.1: -->Overview of Important Properties of Electroplated Coatings and their Applications'''</caption>

To reduce the mechanical wear of thin surface layers on sliding and connector contacts , additional lubricants in liquid form are often used. On silver contacts , passivation coatings are applied as protection against silver sulfide formation.

For thin coatings starting from the liquid phase , two processes are used differentiated by the metallic deposition being performed either with or withoutthe use of an external electrical current source. The first one is electroplating , while the second one is a chemical deposition process.

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.

===<!--7.1.2 -->Electroless Plating===

 Electroless plating is defined as a coating process which is performed without the use of an external current source. It allows a uniform metal coating , independent 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).

==<!--7.2 -->Coatings from the Gaseous Phase (Vacuum Deposition)==The term PVD (physical vapor deposition) defines processes of metal, metal alloys, and chemical compounds deposition in a vacuum by adding thermal and kinetic energy through by particle bombardment. The main processes are the following four coating variations (<xr id="tab:Characteristics of the Most Important PVD Processes"/> <!--(Table 7.6-->):

In all four processes , the coating material is transported in its atomic form to the substrate and deposited on it as a thin layer (a few nm to approx. 10 μm)

<caption>'''<!--Table 7.6: -->Characteristics of the Most Important PVD Processes'''</caption>

The sputtering process has gained the economically most significant usage. Its process principle is illustrated in (<xr id="fig:Principle of sputtering"/> <!--(Fig. 7.5)-->).

[[File:Principle of sputtering.jpg|right|thumb|Figure 1: Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms]]

Initially , a gas discharge is ignited in a low pressure (10^-1 -1 Pa) argon atmosphere. The argon ions generated , are accelerated in an electric field and impact the target of material to be deposited with high energy. Caused by this energy , atoms are released from the target material which condensate on the oppositely arranged anode (the substrate) and form a layer with high adhesion strength. Through an overlapping magnetic field at the target location , the deposition rate can be increased, making the process more economical.

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"/>).

*'''<figure id="fig:Examples of vacuum coated semi-finished materials and parts'''">[[File:Examples of vacuum coated semi finished materials and parts.jpg|left|Figure 2: Examples of vacuum coated semi finished materials and parts]]</figure>

For the geometry of semi-finished products to be coated , there are few restrictions. Only the coating of the inside of machined holes and tubing has

Depending on the application , the following parameters are tested and recorded (see also: Electroplating of parts):

These quality tests are performed according to industry standards, internal standards, and customer specifications resp.

==<!--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

<caption>'''<!--Table 7.7: -->Comparison of different coating processes'''</caption>

The main differences between the coating processes are found in the coating materials and thickness. While mechanical cladding and sputtering allow theuse of almost any alloy material, electroplating processes are limited to metals and selected alloys , such as for example high-carat gold alloys with up to .3 wt% Co or Ni. Electroplated and sputtered surface layers have a technological and economical upper thickness limit of about 10μm. While mechanical cladding has a minimum thickness of approx. 1 μm, electroplating and sputtering can also be easily applied in very thin layers down to the range of 0.1 μm.

The properties of the coatings are closely related to the coating process. Starting materials for cladding and sputtering targets precious metals and their alloys , which in the case of gold and palladium based materials , are vacuum melted and therefore exhibit a very high purity. During electroplating, depending on the type of electrolytes and the deposition parameters, some electrolyte components such as carbon and organic compounds are incorporated into the precious metal coating. Layers deposited from the gaseous phase however are very pure.

==<!--7.4 -->Hot (-Dipped) Tin Coated Strip Materials==During hot-dip tinning , pre-treated strip materials are coated with pure tin or tin alloys from a liquid solder metal. During overall (or all-around) tinning the stripsthrough strips through a liquid metal melt. For strip tinning , rotating rolls are partially immersed into a liquid tin melt and transport the liquid onto the strip , which is guided above them. Through special wiping and gas blowing procedures , the deposited tin layer can be held within tight tolerances. Hot tinning is performed directly onto the base substrate material without any pre-coating with either copper or nickel. Special cast-on processes or the melting of solder foils onto the carrier strip allow , also allows the production of thicker solder layers (> 15 μm).

The main advantage of hot tinning of copper and copper alloys as , compared to tin electroplating , is the formation of an inter-metallic copper-tin phase (Cu₃Sn, Cu₆Sn₅) 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 tinning process, is rather hard and reduces in connectors the frictional force and mechanical wearin connectors. Tin coatings produced by hot tinning have a good adhesion to the substrate material and do not tend to tin whisker formation.

A special process of hot tinning is the “Reflow” process. After depositing a tin coating by electroplating , the layer is short-time melted in a continuous process.

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"/>).

*'''<figure id="fig:Typical examples of hot tinned strip materials'''">[[File:Typical examples of hot tinned strip materials.jpg|left|Figure 3: Typical examples of hot tinned strip materials]]<br style="clear:both;"/></figure>

==<!--7.5 -->Contact Lubricants==By using suitable lubricants , the mechanical wear and frictional oxidation of sliding and connector contacts can be substantially reduced. In the electrical contact technology , solid, as well as high and low viscosity liquid lubricants are used.

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. 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-propylenealcohol during the application to contact parts. After evaporation of the alcohol a thin and uniform layer of lubricant is retained on the contact surfaces.  *'''Properties of the Synthetic DODUCONTA Contact Lubricants'''

<table class="twocolortable"><tr><th>Lubricant</th><th colspan="5">DODUCONTA</th></tr><th></th><th>B5</th><th>B9</th><th>B10</th><th>B12K</th><th>B25</th><tr><td><p class="s8">Contact force</p></td><td><p class="s8">&gt;1N</p></td><td><p class="s8">0Among the various contact lubricants offered on the market, contact lubrication oils have shown performance advantages.1 They are mostly synthetic, chemically inert and silicone- 2N</p></td><td><p class="s8">&lt; 0free oils which differ in their chemical composition and viscosity.2N</p></td><td><p class="s8">0.2 - 5N</p></td><td><p class="s8">&lt;1N</p></td></tr><tr><td><p class="s8">Density (20°C)</p><p class="s8">[g/cm³]</p></td><td><p class="s8">1.9</p></td><td><p class="s8">1.0</p></td><td><p class="s8">0.92</p></td><td><p class="s8">1.0</p></td><td><p class="s8">1.0</p></td></tr><tr><td><p class="s8">Specificel. Resis-</p><p class="s8">tance [<span class="s9">S · </span>cm]</p></td><td/><td><p class="s8">2 x 10¹⁰</p></td><td><p class="s8">10¹⁰</p></td><td><p class="s8">6 x 10⁹</p></td><td><p class="s8">5 x 10⁸</p></td></tr><tr><td><p class="s8">Viscosity (20°C)</p><p class="s8">[mPa·s]</p></td><td><p class="s8">325</p></td><td><p class="s8">47</p></td><td><p class="s8">21</p></td><td><p class="s8">235</p></td><td><p class="s8">405</p></td></tr><tr><td><p class="s8">Congeal temp.[°C]</p></td><td/><td><p class="s8">-55</p></td><td><p class="s8">-60</p></td><td><p class="s8">-40</p></td><td><p class="s8">-35</p></td></tr><tr><td><p class="s8">Flash point[°C]</p></td><td/><td><p class="s8">247</p></td><td><p class="s8">220</p></td><td><p class="s8">238</p></td><td><p class="s8">230</p></td></tr></table>

<table class="twocolortable" style="text<!-align: left; font-size: 12px;width:80%"><tr><th><p class="s8">Lubricant</p></th><th><p class="s8">Applications</p></th></tr><tr><td><p class="s8">DODUCONTA B5</p></td><td><p class="s8">Current collectors, connectors, slider switches</p></td></tr><tr><td><p class="s8">DODUCONTA B9</p></td><td><p class="s8">Wire potentiometers, slip rings, slider switches, measuring range selectors, miniature connectors</p></td></tr><tr><td><p class="s8">DODUCONTA B10</p></td><td><p class="s8">Precision wire potentiometers, miniature slip rings</p></td></tr><tr><td><p class="s8">DODUCONTA B12K</p></td><td><p class="s8">Wire potentiometers, slider switches, miniature slip rings, connectors</p></td></tr><tr><td><p class="s8">DODUCONTA B25</p></td><td><p class="s8">Current collectors, measuring range selectors, connectors</p></td></tr></table> ==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, or be otherwise they are easily broken by the applied contact force.

[[File:Typical process flow for the SILVERBRITE W ATPS process.jpg|right|thumb|Figure 4: Typical process flow for the SILVERBRITE W ATPS process]]

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

negatively affected. Because of its chemical composition , this protective layer has some lubricating properties which reduce the insertion and withdrawal forces of connectors noticeably. <xr id="fig:Typical process flow for the SILVERBRITE W ATPS process"/> '''Typical process flow for the SILVERBRITE W ATPS process'''