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"/>).

*'''Quality criteria''' Besides others For the following layer parameters geometry of semi-finished products to be coated, there are typically monitored in-process few restrictions. Only the coating of the inside of machined holes and documented:tubing haslimitations.

*Coating thickness *Solderability*Adhesion strength *Bonding property*Porosity Contact *resistance'''Tolerances'''

These quality tests are performed according to industry standardsCoating thickness &#177;10 - 30 %, internalstandards, and customer specifications resp.depending on the thickness

===7.1.1.3 Electroplating of Semi-finished Materials===*'''Quality criteria'''The process for overall electroplating of strips, profiles, and wires is mostlyperformed Depending on continuously operating reel-to-reel equipment. The processingsteps for the individual operations such as pre-cleaningapplication, electroplating, rinsingthe following parameters are following the same principles as those employed in tested and recorded (see also: Electroplating of parts electroplating.):

===7.1.1.4 Selective Electroplating===Since precious metals These quality tests are rather expensive it is necessary performed according to perform theelectroplating most economically industry standards, internal standards and coat only those areas that need the layersfor functional purposes. This leads from overall plating to selectiveelectroplating of strip material in continuous reel-to-reel processes. Dependingon the final parts design and the end application the processes can be appliedto solid strip material as well as pre-stamped and formed continuous strips orutilizing wire-formed or machined pins which have been arranged as bandoliersattached to conductive metal stripscustomer specifications resp.

==<!--7.3-->Comparison of Deposition Processes==The core individual deposition processes have in part of selective precious metal electroplating is the actualelectroplating celldifferent performance characteristics. In it For each end application, the anode is arranged closely optimal process has to the cathodic polarizedmaterial stripbe chosen, considering all technical and economical factors. Cathode screens or masks may The main selection criteria should be applied between based on the two tofocus electrical and mechanical requirements for the electrical field onto closely defined spots contact layer and on the cathode stripdesign 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.

Special high performance electrolytes are used in selective electroplating toreach short plating times and allow a high flow rate The electroless metal coating is not covered here because of the electrolyte low thickness of deposits, which makes them in most cases not suitable for a fastcontactelectrolyte exchange in the actual coating areaapplications.

Fig<figtable id="tab:Comparison of different coating processes"><caption>'''<!--Table 7. 7.1:Brush (or “Tampon”) plating cell;1 Strip; 2 Anode; 3 Electrolyte feed;4 Felt covered cell-->Comparison of different coating processes'''</caption>

For special applications, such as for example electronic component substrates{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Process / Coating Properties!Mechanical Processes (Cladding)!Electroplating!Vaccum Deposition (Sputtering)|-|Coating material|formabe metal and alloys|metals,alloys only limited|metals and alloys|-|Coating thickness|> 1μma dot shaped precious metal coating is required|0.1 - approx. This is achieved with two belt10 μm <br />(in special cases up to 100 μm)masks running synchronous to the carrier material|0.1 approx. One 10 μm|-|Coating configuration|selectively, stamping edges not coated|all around and selectively<br />stamping edges coated|mostly selectivity|-|Adhesion|good|good|very good|-|Ductility|good|limited|good|-|Purity|good|inclusions of these two masks hasforeign materialswindows which are open to the spot areas targeted |very good|-|Porosity|good|good for precious metal plating> approx. 1μm|good|-|Temperature stability|goodvery good|good|very good|-|Mechanical wear|little|very little|little|-|Environmental impact|little|significant|none|}coverage.</figtable>

===Summary The main differences between the coating processes are found in the coating materials and thickness. While mechanical cladding and sputtering allow the use of the almost any alloy material, electroplating processes are limited to metals and selected alloys, such as for selective 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.

*'''Immersion electroplating'''Overall or selective 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 both sides of solid strips or pre-stampedparts in strip formelectrolytes 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.

*'''Stripe electroplating'''==<!--7.4-->Hot (-Dipped) Tin Coated Strip Materials==Stripe electroplating on solid 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 strips through wheel cells 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 using maskingtechniquesthe melting of solder foils onto the carrier strip, also allows the production of thicker solder layers ( > 15 μm).

*'''Selective The main advantage of hot tinning of copper and copper alloys, compared to tin electroplating'''One, is the formation of an inter-metallic copper-sided selective coating of solidtin phase (Cu₃Sn, Cu₆Sn₅) at the boundary between the carrier material and the tin layer. This thin (0.3 – 0.5 μm) intermediate layer, pre-stampedwhich is formed during the thermal tinning process, or metallically belt-linkedstrips is rather hard and reduces the frictional force and mechanical wear in connectors. Tin coatings produced by brush platinghot tinning have a good adhesion to the substrate material and do not tend to tin whisker formation.

*'''Spot A special process of hot tinning is the “Reflow” process. After depositing a tin coating by electroplating'''Electroplating in spots of solid strips with guide holes or pre, the layer is short-stamped parts time melted ina continuous process.strip formThe 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 electroplated semi-finished hot tinned strip materials=== (overall or selectively"/>)bild.

 <table border="1" cellspacing="0" style="border-collapseCoating materials:collapse"><tr><td><p class="s8">Type of Coatings</p></td><td><p class="s8">Coating Thickness</p></td><td><p class="s8">Remarks</p></td></tr><tr><td><p class="s8">Precious Metals</p></td><td/><td/></tr><tr><td><p class="s8">Pure gold</p><p class="s8">Hard gold (AuCo 0.3)</p></td><td><p class="s8">0.1 - 3 µm</p></td><td><p class="s8">In special cases up to 10 µm</p></td></tr><tr><td><p class="s8">Palladium-nickel (PdNi20)</p></td><td><p class="s8">0.1 - 5 µm</p></td><td><p class="s8">Frequently with additional 0.2 µm AuCo 0.3</p></td></tr><tr><td><p class="s8">Silver</p></td><td><p class="s8">0.5 - 10 µm</p></td><td><p class="s8">In special cases up to 40 µm</p></td></tr><tr><td><p class="s8">Non-precious Metals</p></td><td/><td/></tr><tr><td><p class="s8">Nickel</p></td><td><p class="s8">0.5 - 4 µm</p></td><td><p class="s8">Diffusion barrier especially for gold layers</p></td></tr><tr><td><p class="s8">Copper</p></td><td><p class="s8">1 - 5 µm</p></td><td><p class="s8">Intermediate layer used in tinning of CuZn</p></td></tr><tr><td><p class="s8">Tintin, tin alloys</p></td><td><p class="s8">0.8 - 25 µm</p></td><td><p class="s8"br>Substrate materials</p></td></tr></table> *'''Carrier Materials'''Copper: Cu, copper alloysCuZn, nickelCuNiZn, nickel alloysCuSn, stainless steelCuBe and others<br />

{| class="twocolortable" style="text-align: left; font-size: 12px;width:40%"Bild |-|Width of tinning: DimensionsCarrier thickness d= 0.1 - |&#8805; 3 &#177; 1 mmCarrier width B= 6 |- 130 mmDistance b > 2 mm|Thickness of tinning: Coating width a= 2 |1 - 30mm15 μmCoating thickness s = 0.2 |- 5 μm|Tolerances (typical rangethickness): Distance from edge b > 0.5 mm|&#177; 1 - &#177; 3 μm depending on the carrier tin thicknessand the plating process *'''Tolerances'''Coating thickness approx. 10 %Coating thickness and position + 0,5 mm|}

Mechanical properties strength and dimensional tolerances of hot tinned strips are closely related to the carrier materials followthe typical standards, i.e. standard for Cu and Cu alloy strips according to DIN EN 1652 and DIN EN 1654 for copper and copper alloys.Depending on the application Quality criteria for the following parameters actual tin coatings are tested andrecorded (see also: Electroplating of parts):usually agreed upon separately.

These quality tests are performed according Contact lubricants have to industry standards, internalstandards, and customer specifications resp.fulfill a multitude of technical requirements:

===7*They must wet the contact surface well; after the sliding operation the lubrication film must close itself again, i.1e.2 Electroless Plating===mechanical interruptions to heal*They should not transform into resins, not evaporate, and not act as dust collectors*The lubricants should not dissolve plastics, they should not be corrosive to non-precious metals or initiate cracking through stress corrosion of plastic components*The specific electrical resistance of the lubricants cannot be so low that wetted plastic surfaces lose their isolating properties*The lubricant layer should not increase the contact resistance; the wear reducing properties of the lubricant film should keep the contact resistance low and consistent over the longest possible operation time

===7Solid lubricants include for example 0.105 – 0.2.1 Introduction===Electroless plating is defined μm thin hard gold layers, which are added as a coating process which is performed withoutthe use of an external current source. It allows a uniform metal coatingindependent of the geometrical shape of the parts to be coated. Because of thevery good dispersion capability surface layers on top of the used electrolytes also cavities and theinside 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 actual contact material serves as a reduction agent (Immersionprocesses) and those in which a reduction agent is added to the electrolyte(Electroless processes).

===7.1.2.2 Immersion Processes===The immersion processes are usually applied in Among the plating of various contact lubricants offered on the metals goldmarket,silvercontact lubrication oils have shown performance advantages. They are mostly synthetic, chemically inert and tin. If the material to be coated is less precious, i.e. exhibits anegative standard potential against the metal ions silicone-free oils which differ in the surrounding solution, itgoes into solution releasing electrons while the more precious metal ions arereduced by absorbing electrons their chemical composition and being deposited on the electrode. Thisprocess can continue until the complete surface of the substrate is coveredwith a thin layer of the more precious metal. This limits the maximum achievablelayer thickness to approx. 0.1 μm ''(Table 7.5)''viscosity.

Table 7.5: Immersion Gold ElectrolytesFor sliding contact systems with contact forces <table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s8">Type of Electrolyte</p></td><td><p class="s8">pH-Range</p></td><td><p class="s8">Coating Properties</p>50 cN and higher sliding speeds, oils with a lower viscosity (</td><td><p class="s8">Application Ranges</p></td></tr><tr><td><p class="s8">Type of Electrolyte</p></td><td><p class="s8">pH-Range</p></td><td><p class="s8">Hardness</p><p class="s8">HV 050 mPa·s) are preferential.025</p></td><td><p class="s8">Punity</p></td><td><p class="s8">Application Ranges</p></td></tr><tr><td><p class="s8">Immersion Gold electrolytes</p></td><td/><td/><td/><td/></tr><tr><td><p class="s8">AUROL 4</p><p class="s8">AUROL 16</p><p class="s8">AUROL 20</p></td><td><p class="s8">3For applications with higher contact forces and operating at higher temperatures, contact oils with a higher viscosity are advantageous.8 - 4Contact oils are mainly suited for applications at low current loads.2</p><p class="s8">5.8 - 6.2</p><p class="s8">5.8 - 6.2</p><p class="s8">5.8 - 6.2</p></td><td><p class="s8">60 - 80</p><p class="s8">60 - 80</p><p class="s8">60 - 80</p><p class="s8">60 - 80</p></td><td><p class="s8">99.99% Au</p><p class="s8">99.99% Au</p><p class="s8">99.99% Au</p><p class="s8">99.99% Au</p></td><td><p class="s8">Thin gold layers on NiAt higher loads and in situations where contact separation occurs during the sliding operation, Ni alloysthermal decomposition may be initiated,</p><p class="s8">Fe and Fe alloys for PCB technology and technical applications</p></td></tr></table>which causes the lubricating properties to be lost.

Otherwise a “wild” uncontrollable deposition would occur==<!--7. In most cases6-->Passivation of Silver Surfaces==palladium The formation of silver sulfide during the shelf life of components with silver surface in sulfur containing solutions 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 used 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 activation SILVERBRITE W ATPS process]]</figure>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 seed barely changes theappearance and only slightlysurfaces with palladium and act increases the good electrical properties such as catalysts in for example the copper contact resistance. The good solderability and nickelbond properties of silver are notelectrolytesnegatively affected. Because of its chemical composition, this protective layer has some lubricating properties which reduce the insertion and withdrawal forces of connectors noticeably.

These electrolytes are usually operating at elevated temperatures Vinaricky, E. (50° – 90°CHrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.The deposits contain besides the metals also process related foreign inclusionssuch as for example decomposition products of the reduction agents.The electroless processes are used mainly for copperSpringer-Verlag, nickel, and golddeposits.Heidelberg 2002

===7Ganz, J.1; Heber, J.2; Macht, W.4 Electroless Deposition of Nickel/Gold===; Marka, E.: Galvanisch erzeugteEdelmetallschichten für elektrische Kontakte. Metall 61 (2007) H.6, 394-398

Electroless deposited nickel coatings with an additional immersion layer of goldare seeing increased importance Song, J.: Edelmetalle in the coating of printed circuit boards (PCBs)Steckverbindungen - Funktionen und Einsparpotential.The process sequence is shown in ''VDE - Fachbericht 67 (Fig. 7.22011)'' using the example of theDODUCHEM process.13-22

After the pre-cleaning (degreasing and etching) a palladium sulfate activator isused which activates the exposed copper surfaces on the printed circuit boardand thus facilitates the nickel depositionJohler, W. The electroless working chemicalnickel electrolyte contains – besides other ingredients – Sodium-hypophosphite; Pöffel,which is reduced to phosphorus in a parallel occurring process andincorporated into the nickel depositK. At the temperature of 87 – 89°C a veryhomogeneous nickel-phosphorus alloy layer with approx; Weik, G. 9 wt% P is depositedwith layer thicknesses > 5 μm possible; Westphal, W. During a consecutive processing step: High Temperature Resistancea very thin and uniform layer (< 0th Galvanically Deposited Gold Layers for Switching Contacts.1 μm) of gold is added in an immersionelectrolyteProc. This protects the electroless nickel layer against corrosion achieving15 Holma solderable and well bondable surface for thick or fine aluminum bond wiresConf.on Electrical Contacts, Chicago (2005) 48-54

It is possible to enhance this layer combination further by adding a immersionGrossmann, H. Schaudt, G.: Untersuchung über die Verwendbarkeit vonpalladium layer between the electroless nickel and the gold coatingÜberzügen der Platinmetallgruppe auf elektrotechnischen Verbindungselementen.Galvanotechnik 67 (DODUBOND process1976). This Pd layer acts as a diffusion barrier and allows theusage of this surface combination also for gold wire bonding.292-297

As an alternativeGrossmann, for gold wire bonding applications a thicker gold layer of 0H.2 –0.5 μm can be applied using an electroless process; Vinaricky, E. Typical electrolytes work at: Edelmetalleinsparung in der Elektrotechnik durcha temperature of approxselektives Galvanisieren. 80°C with deposition rates of 0In: Handbuch der Galvanotechnik.3 – 0.4 μm per 30München, Hanser-minutes. There are however limitations with these electroless electrolytesconcerning their stability and the robustness of the process compared to otherelectroplating processes which reduces their wider usage ''Verlag, 37 (Fig. 7.31981)''.132-141

FigGrossmann, H. 7; Schaudt, G.3:Hochgeschwindigkeitsabscheidung von EdelmetallenCoating compositionof a printed circuit board withreductively enhanced goldauf Kontaktwerkstoffen. Galvanotechnik 84 (1993) H.5, 1541-1547

===7Bocking, C.1.2; Cameron, B.5 Immersion Deposition : The Use of Tin===High Speed Selective JetA tin coating by ion exchange is usually not possible since copper is Electrodeposition of Gold for the moreprecious metalPlating of Connectors. By adding thio-urea the electro-chemical potential of copper isreduced to a level (approxTrans. 450 mV, significantly lower than tin) that allows theexchange reactionIMF. Using a suitable electrolyte composition and enhancersolutions like with the DODUSTAN process ''72 (Fig. 7.41994)'' tin coatings can beproduced that, even under usually unfavorable conditions of copperconcentrations of 7 g/l in the electrolyte, are well solderable.33-40

FigEndres, B. 7: Selektive Beschichtungen von Kontaktmaterial imDurchzugsverfahren.4: Process flow for electroless tin deposition using the DODUSTAN processMetalloberfläche 39 (1985) H.11, 400-404

The immersion tin deposition is suitable for the production of a well solderableKaspar, F.; Marka, E.; Normann, N.: Eigenschaften von chemisch Nickelsurface on printed circuit boards and electronic componentsGoldschichten für Baugruppen der Elektrotechnik. It is also used asan etch resist against ammonia based solutions or as corrosion and oxidationprotection of copper surfaces.VDE Fachbericht 47 (1995) 19-27

===7Schmitt; W.2 Coatings from the Gaseous Phase (Vacuum Deposition)===The term PVD (physical vapor deposition) defines processes of metal; Kißling, metalalloysS.; Behrens, and chemical compounds deposition in a vacuum by adding thermal andV.: Elektrochemisch hergestelltekinetic energy through particle bombardmentSchichtsysteme auf Aluminium für Kontaktanwendungen. The main processes are thefollowing four coating variations ''VDE - Fachbericht 67 (Table 7.62011)'':136-141

*Vapor deposition *Sputtering Freller, H.: Moderne PVD-Technologien zum Aufbringen dünnerKontaktschichten. VDE-Fachbericht 40 (Cathode atomization1989)*Arc vaporizing *Ion implantation33-39

In all four processes the coating material is transported in its atomic form to thesubstrate and deposited on it as a thin layer Ganz, J.: PVD-Verfahren als Ergänzung der Galvanik. Metalloberfläche 45 (a few nm to approx. 10 μm1991)

Table 7Schmitt, W.; Franz, S.; Heber, J.; Lutz, O.; Behrens, V.6: Formation of SilverSulfide Layers and their Influence on the Electrical Characteristics of Contacts inth the Most Important PVD ProcessesField of Information Technology. Proc. 24 Int. Conf.on Electr. Contacts,Saint Malo, France (2008) 489-494

The sputtering process has gained the economically most significant usageGehlert, B.: Edelmetalllegierungen für elektrische Kontakte. Itsprocess principle is illustrated in ''Metall 61 (Fig. 7.52007)''H.6, 374-379

FigGanz, J. 7: Einsatz von Sputterverfahren bei komplexenBeschichtungsaufgaben.5: Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atomsJOT 11 (1997)

Initially a gas discharge is ignited in a low pressure (10 – 1 Pa) argonatmosphereBuresch, I.; Bögel, A.; Dürrschnabel, W. The argon ions generated are accelerated in an electric field andimpact the target of material to be deposited with high energy: Tin Coating for Electrical Components. Caused by thisenergy atoms are released from the target material which condensate on theoppositely arranged anode Metall 48 (the substrate1994) and form a layer with high adhesionstrengthH. Through an overlapping magnetic field at the target location thedeposition rate can be increased1, making the process more economical.11-14

*High purity of the deposit layers *Low thermal impact on the Adler, U.; Buresch, I.; Riepe, U.; Tietz, V.: Charakteristische Eigenschaften der*Almost unlimited coating materials substrateschmelzflüssigen Verzinnung von Kupferwerkstoffen.*Low coating thickness tolerance *Excellent adhesion VDE-Fachbericht 63 (also by using additional intermediate layers2007)175-180

Coatings produced by PVD processes are used for contact applicationsHuck, forexample on miniatureM.: Einsatz von Schmiermitteln auf Gleit-profiles, in electrical engineering and for electronicund Steckkontakten.components, for solderability in joining processes, for metalizing of nonconductivematerials, as well as in semiconductors, optoMetalloberfläche (1982) 429-electronics, optics,and medical technology applications.435

There are few limitations regarding the geometrical shape of substrate partsAbbott, W.,H.Only the interior coating : Field and Laboratory Studies of drilled holes and small diameter tubing can be moreCorrosion Inhibiting Lubricantsproblematic (ratio of depth to diameter should be < 2:1)for Gold-Plated Connectors. Proc. HOLM Conf. Profile wires, stripson Electrical Contacts,Chicagoand foils can be coated from one side or both; formed parts can be coatedselectively by using masking fixtures that at the same time serve as holdingfixtures.(1996) 414-428

*'''Examples Noel, S.; Alarmaguy, D.; Correia, S.; Gendre, P.: Study of vacuum coated semi-finished materials and parts'''Thin Underlayers tobildHinder Contact resistance Increase Due to Intermetallic Compound Formation.th Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, BC,Canada (2009) 153 – 159

<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s8">Substrate Materials</p></td><td><p class="s8">Coating Materials</p></td></tr><tr><td><p class="s8">Substrate Materials</p></td><td><p><span>Ag</span></p></td><td><p><span>Au</span></p></td><td><p><span>Pt</span></p></td><td><p><span>Pd</span></p></td><td><p><span>Cu</span></p></td><td><p><span>Ni</span></p></td><td><p><span>Ti</span></p></td><td><p><span>Cr</span></p></td><td><p><span>Mo</span></p></td><td><p><span>W</span></p></td><td><p><span>Ai</span></p></td><td><p><span>Si</span></p></td></tr><tr><td><p class="s8">Precious metal / alloys</p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">NF metals / alloys</p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">Fe alloys / stainless steel</p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">Special metals (Ti, MoBuresch, W)</p></td><td><p><span>[[File:K7-leer.png]]</span></p></td><td><p><span>[[File:K7-gefI.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-leer.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">Carbide steels (WC-Co)</p></td><td><p><span>[[File:K7-leer.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-leer.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">Ceramics (Al<span class="s16">2</span>O<span class="s16">3</span>; Hack, AlN)</p></td><td><p><span>[[File:K7-leerM.png]]</span></p></td><td><p><span>[[File:K7-leerEigenschaften von Zinnschichten für elektromechanischeBauelemente – Einflussfaktoren und ihre Auswirkungen.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-leer.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">Glasses (SiO<span class="s16">2</span>VDE – Fachbericht 65, CaF)</p></td><td><p><span>[[File:K7-leer.png]]</span></p></td><td><p><span>[[File:K7-leer.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-leer.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">Plastics (PA, PPS2009)</p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></p></td></tr></table>23 – 30

*'''Dimensions''' DimensionsCoating thickness: 10 nm - 15 μmCoating thicknesses for contact applications: 0.1 - 10 μm For the geometry of semi-finished products to be coated there are fewrestrictions. Only the coating of the inside of machined holes and tubing haslimitations. *'''Tolerances''' Coating thickness +10 - 30 %Buresch, depending on the thickness *'''Quality criteria'''Depending on the application the following parameters are tested and recorded(see also: Electroplating of parts): *Coating thickness *Solderability *Adhesion strength *Bonding property*Porosity *Contact resistance  These quality tests are performed according to industry standards, internalstandards, and customer specifications respI. ===7.3 Comparison of Deposition Processes===The individual deposition processes have in part different performancecharacteristics. For each end application the optimal process has to be chosenconsidering all technical and economical factors. The main selection criteriashould be based on the electrical and mechanical requirements for the contactlayer and on the design characteristics of the contact component. Table 7.7gives some indications for a comparative evaluation of the different coatingprocesses. The electroless metal coating is not covered here because of the low thicknessof deposits which makes them in most cases not suitable for contactapplications. Table 7.7: Comparison of different coating processes The main differences between the coating processes are found in the coatingmaterials and thickness. While mechanical cladding and sputtering allow theuse of almost any alloy material, electroplating processes are limited to metalsand selected alloys such as for example high-carat gold alloys with up to .3wt% Co or Ni. Electroplated and sputtered surface layers have a technologicaland economical upper thickness limit of about 10μm. While mechanical claddinghas a minimum thickness of approx. 1 μm, electroplating and sputteringcan 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 theiralloys which in the case of gold and palladium based materials are vacuummelted and therefore exhibit a very high purity. During electroplating, dependingon the type of electrolytes and the deposition parameters, some electrolytecomponents such as carbon and organic compounds are incorporated intothe precious metal coating. Layers deposited from the gaseous phase howeverEffekte intermetallischer Phasen auf die Eigenschaften vonare very pureZinnoberflächen auf Kupferlegierungen. ===7.4 Hot (-Dipped) Tin Coated Strip Materials===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 VDE – 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. *'''Typical examples of hot tinned strip materials'''bild *'''Materials'''Coating materials: Pure tin, tin alloysSubstrate materials: Cu, CuZn, CuNiZn, CuSn, CuBe and others *'''Dimensions and Tolerances'''Width of tinning: > 3 + 1 mmThickness of tinning: 1 - 15 μmTolerances Fachbericht 67 (thickness2011): + 1 - +3 μm depending on tin thickness *'''Quality Criteria'''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.Quality criteria for the actual tin coatings are usually agreed upon separately. 7.5 Contact LubricantsBy 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. Contact lubricants have to fulfill a multitude of technical requirements: *They must wet the contact surface well; after the sliding operation the lubrication film must close itself again, i.e. mechanical interruptions to heal*They should not transform into resins, not evaporate, and not act as dust collectors*The lubricants should not dissolve plastics, they should not be corrosive to non38-precious metals or initiate cracking through stress corrosion of plastic components*The specific electrical resistance of the lubricants cannot be so low that wetted plastic surfaces lose their isolating properties*The lubricant layer should not increase the contact resistance; the wear reducing properties of the lubricant film should keep the contact resistance low and consistent over the longest possible operation time46

Solid lubricants include for example 0Schmitt, W.05 ; Heber, J.; Lutz, O.; Behrens, V.: Einfluss des Herstellverfahrens aufdas Korrosions- und Kontaktverhalten von Ag – 0.2 μm thin hard gold layers whichBeschichtungen inare added as surface layers on top of the actual contact materialschwefelhaltiger Umgebung.VDE – Fachbericht 65 (2009) 51 – 58