Besides manufacturing contact materials from the solid phase, i.e. by melt orpowder metallurgy, the production starting in the liquid or gaseous phase isgenerally preferred when thin layers in within the μm range are required , which cannotbe obtained economically by conventional cladding methods(<xr id="tab:Overview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications"/><!--(Tab. 7.1)-->). Such coatingsfulfill different requirements depending on their composition and thickness.They can serve as corrosion or wear protection or can fulfill the need for thincontact layers for certain technical applications. In addition they serve fordecorative purposes as a pleasing and wear resistant surface coating.

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

To reduce the {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Properties!Applications!Examples|-|Color|Pleasing appearance|Brass plated lamps and furniture hardware|-|Luster|Decorative appearance, Light reflection|Chrome plated fixtures, silver coated mirrors|-|Hardness / Wear Resistance|Prolonging of mechanical wear life|Hard chrome plated tools|-|Sliding properties|Improvement of thin dry sliding wear|Lead-tin-copper alloys for slide bearings|-|Chemical stability|Protection against chemical effects|Lead-Tin coatings as etch resist on PC boards|-|Corrosion resistance|Protection against environmental corrosion|Zinc coatings on steel parts|-|Electrical conductivity|Surface conduction of electrical current|Conductive path on PC boards|-|Thermal conductivity|Improved heat conduction on the surface |Copper plated bottoms for cookware|-|Machining capability|Shaping through machining|Copper coatings on low pressure cylinders|-|Magnetic properties|Increase of coercive force [[#text-reference|^*)]] |Cobalt-nickel layers on sliding magnetic storage media|-|Brazing and connectorsoldering|Brazing without aggressive fluxes|Tin-Lead coatings on PC board pathscontacts additional lubricants |-|Adhesion strength|Improvement of adhesion|Brass coating on reinforcement steel wires in liquid form are often used. On silver contactstires|-|Lubricating properties|Improvement of formability|Copper plating for wire drawing|}</figtable>passivation coatings are applied as protection against silver sulfide formation.<div id="text-reference">*) Coercive force= force to retaim the adopted magnetisation</div>

===7.1 Coatings from To reduce the Liquid Phase===For mechanical wear of thin coatings starting from the surface layers on sliding and connector contacts, additional lubricants in liquid phase two processes form are often useddifferentiated by the metallic deposition being performed either with or withoutthe use of an external electrical current source. The first one is electroplatingwhile the second one is a chemical deposition processOn silver contacts, passivation coatings are applied as protection against silver sulfide formation.

===7.1.1 Electroplating (or Galvanic Deposition)=Coatings from the Liquid Phase==For electroplating of metalsthin coatings starting from the liquid phase, especially precious metals, water based solutions(electrolytes) two processes are used which contain differentiated by the metals to be deposited as ions (i.e.dissolved metal salts). An electric field between metallic deposition being performed either with or without the anode and the work piecesas the cathode forces the positively charged metal ions to move to the cathodewhere they give up their charge and deposit themselves as metal on the surfaceuse of the work piece.Depending on the application, for electric and electronic or decorative end use,different electrolytic bath solutions (electrolytes) are usedan external electrical current source. The first one is electroplatingequipment used for precious metal plating and its complexity varies widelydepending on , while the second one is a chemical deposition process technologies employed.Electroplating processes are encompassing besides the pure metal depositionalso preparative and post treatments of the goods to be coated. An importantparameter for creating strongly adhering deposits is the surface of the goods tobe metallic clean without oily or oxide film residues. This is achieved throughvarious pre-treatment processes specifically developed for the types of materialand surface conditions of the goods to be plated.In the following segments electrolytes – both precious and non-precious – aswell as the most widely used electroplating processes are described.

===7.1.1.1 Electroplating Solutions – Electrolytes(or Galvanic Deposition)===The actual 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 deposition occurs in salts). An electric field between the electrolytic solution which containsanode and the plating material work pieces as the cathode, forces the positively charged metal ionsto move to the cathode where they give up their charge and deposit themselves as metal on the surface of the work piece. Besides this basic ingredientDepending on the application, the for electric and electronic or decorative end use, different electrolytic bath solutions (electrolytescontain additional components ) are used. The electroplating equipment used for precious metal plating and its complexity varies widely, depending on the process technologies employed.Electroplating processes usedare encompassing, besides the pure metal deposition, such as also preparative and post treatments of the goods to be coated. An important parameter forexample conduction salts, brightenerscreating 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 organic additives which are codepositedsurface conditions of the goods to be plated.into In the coatingsfollowing segments, influencing the final properties of electrolytes – both precious and non-precious – as well as the most widely used electroplatingdepositprocesses are described.

===7.1.1.1.1 Precious Metal Electrolytes===All precious metals can be electroplated with silver and gold by far the mostwidely used ones ''Main Articel: [[Electroplating (or Galvanic Deposition)| Electroplating (Tables 7.1 and 7.2or Galvanic Deposition)''.The following precious metal electrolytes are the most important ones:]]

*'''Gold electrolytes''' For functional and decorative purposes pure gold, hard gold, low===<!-karat gold, or colored gold coatings are deposited-7. Depending on the requirements, acidic, neutral, or cyanide electrolytes based on potassium gold cyanide or cyanide free and neutral electrolytes based on gold sulfite complexes are used1.2-->Electroless Plating===

*'''Palladium and Platinum electrolytes''' Palladium Electroless plating is mostly deposited defined as a pure coating process which is performed without the use of an external current source. It allows a uniform metalcoating, 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 applications in electrical contacts however also as palladium nickelexample. For higher value jewelry allergy protective palladium intermediate layers In principal, two different mechanisms are used employed for electroless plating: processes in which the carrier material serves as a diffusion barrier over copper alloy substrate materials. Platinum reduction agent (Immersion processes) and those in which a reduction agent is mostly used as a surface layer on jewelry itemsadded to the electrolyte (Electroless processes).

*'''Rhodium electrolytes''' Rhodium deposits are extremely hard ==<!--7.2-->Coatings from the Gaseous Phase (Vacuum Deposition)==The term PVD (HV 700 – 1000physical vapor deposition) defines processes of metal, metal alloys and wear resistant. They also excel chemical compounds deposition in light reflectiona vacuum by adding thermal and kinetic energy by particle bombardment. Both properties The main processes are of value for technical as well as decorative applications. While technical applications mainly require hard, stress and crack free coatings, the jewelry industry takes advantage following four coating variations (<xr id="tab:Characteristics of the light whitish deposits with high corrosion resistanceMost Important PVD Processes"/><!--(Table 7.6-->):

*'''Silver electrolytes''' Silver electrolytes without additives generate dull soft deposits Vapor deposition *Sputtering (HV ~ 80Cathode atomization) which are mainly used as contact layers on connectors with limited insertion and withdrawal cycles. Properties required for decorative purposes such as shiny bright surfaces and higher wear resistance are achieved through various additives to the basic Ag electrolyte.*Arc vaporizing *Ion implantation

Table 7In 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.2: Precious Metal Electrolytes for Technical Applications10 μm)

*<figtable id="tab:Characteristics of the Most Important PVD Processes"><caption>'''Copper electrolytes<!--Table 7.6:-->Characteristics of the Most Important PVD Processes''' Copper electrolytes are used for either depositing an intermediate layer on strips or parts, for building up a printed circuit board structure, or for the final strengthening during the production of printed circuit boards.</caption>

*'''Tin electrolytes''' Pure tin and tin {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Process!Principle!Process Gas Pressure!Particle Energy!Remarks|-|Vapor deposition|Vaporizing in a crucible <br />(electron beam or resistance heating)|10^-3 Pa|< 2eV|Separation of alloy deposits are used as dull or also bright surface layers on surfaces required for soldering. In components may occur|-|Arc vaporizing|Vaporizing of the printed circuit board manufacturing they are also utilized as target <br />plate in an etch resist for electrical arc|10^-1 Pa-1Pa|80eV-300eV|Very good adhesion due to ion bombardement|-|Sputtering|Atomizing of the target plate<br />(cathode) in a gas discharge|10^-1 Pa-1Pa|10eV-100eV|Sputtering of non-conductive pattern design after initial copper electroplating.materials possible through RF operation|-|Ion implantation|Combination of vapor <br />deposition and sputtering|10^-1 Pa-1Pa|80eV-300eV|Very good adhesion from ion bombardment but also heating of the substrate material|}</figtable>

*'''Nickel electrolytes''' Nickel layers are mostly used as diffusion barriers during The sputtering process has gained the gold plating economically most significant usage. Its process principle is illustrated in (<xr id="fig:Principle of copper and copper alloys or as an intermediate layer for tinningsputtering"/><!--(Fig. 7.5)-->).

*'''Bronze electrolytes''' Bronze coatings – <figure id="fig:Principle of sputtering">[[File:Principle of sputtering.jpg|right|thumb|Figure 1: Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms]]</figure>Initially, a gas discharge is ignited in white or yellow color tones – a low pressure (10^-1 -1 Pa) argon atmosphere. The argon ions generated, are used either as accelerated in an allergy free nickel replacement or as 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 surface layer for decorative purposeswith high adhesion strength. For technical applications Through an overlapping magnetic field at the bronze layers are utilized for their good corrosion resistance and good brazing and soldering propertiestarget location, the deposition rate can be increased, making the process more economical.

Table 7.2The advantages of the PVD processes and especially sputtering for electrical contact applications are: Typical Electrolytes for the Deposition of Non-Precious Metals

===7.1.1.2 Electroplating *High purity of Parts===the deposit layers The complete or all-around electroplating of small mass produced parts like*Low thermal impact on the substrate contact springs, rivets, or pins is usually done as mass plating in electroplating*Almost unlimited coating materials barrels of different shape. During the electroplating process the parts are*Low coating thickness tolerance continuously moved and mixed to reach a uniform coating.*Excellent adhesion (also by using additional intermediate layers)

Larger parts Coatings produced by PVD processes are frequently electroplated used for contact applications, for example on racks either totally or by differentmasking techniques also partially. Penetrating the coating into the interior ofdrilled holes or tubes can be achieved with the use miniature-profiles, in electrical engineering and for electronic components, for solderability in joining processes, for metalizing of special fixturesnonconductive 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===Electroplated Parts===bild"fig:Examples of vacuum coated semi finished materials and parts"/>).

Precious metals: 0Noel, S.; Alarmaguy, D.; Correia, S.2 – 5 μm (typical layer thicknesses; for Ag also up Gendre, P.: Study of Thin Underlayers to 25 μm)Non-precious metals: Up Hinder Contact resistance Increase Due to approxIntermetallic Compound Formation. 20 μmTolerances: Strongly varying depending th Proc. 55 IEEE Holm Conf. on the geometrical shape ofElectrical Contacts, Vancouver, BC,parts Canada (up to 50% at a defined measuring spot2009).It is recommended to specify a minimum value for thecoating thickness at a defined measuring spot153 – 159

These quality tests are performed according to industry standardsSchmitt, internalW.; Heber, J.; Lutz, O.; Behrens, V.: Einfluss des Herstellverfahrens aufdas Korrosions- und Kontaktverhalten von Ag – Beschichtungen instandards, and customer specifications respschwefelhaltiger Umgebung.VDE – Fachbericht 65 (2009) 51 – 58