Changes

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>

{| 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 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 magnetic storage media|-|Brazing and soldering|Brazing without aggressive fluxes|Tin-Lead coatings on PC board paths|-|Adhesion strength|Improvement of adhesion|Brass coating on reinforcement steel wires in tires|-|Lubricating properties|Improvement of formability|Copper plating for wire drawing|}</figtable><div id="text-reference">*) Coercive force= force to retaim the adopted magnetisation</div>  To reduce the mechanical wear of thin surface layers on sliding and connectorcontacts , 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 useddifferentiated 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 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 surfaceof the work piece.Depending on the application, for electric and electronic or decorative end use,different electrolytic bath solutions (electrolytes) are used. The electroplatingequipment 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 that the surface of the goods has 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. 

==== Electroplating Solutions – Electrolytes====The actual metal deposition occurs in the electrolytic solution which containsthe plating material as metal ions. Besides this basic ingredient, the electrolytescontain additional components depending on the processes used, such as forexample conduction salts, brighteners, and organic additives which are codepositedinto the coatings, influencing the final properties of the electroplatingdeposit. ===== Precious Metal Electrolytes=====All precious metals can be electroplated with silver and gold by far the mostwidely used ones ''(Tables <!--7.1 and 7.2)''.The following precious metal electrolytes are the most important ones: Main Articel: [[Precious Metal Electrolytes| Precious Metal Electrolytes]] ==== Electroplating of Parts=-->Electroless Plating===The complete or all-around electroplating of small mass produced parts likecontact springs, rivets, or pins is usually done as mass plating in electroplatingbarrels of different shape. During the electroplating process the parts arecontinuously moved and mixed to reach a uniform coating. Larger parts are frequently electroplated 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 of special fixtures.

<table border="1" cellspacing="0" style="border<!--7.2--collapse:collapse"><tr><td><p class="s9">Coatings</p></td></tr><tr><td><p class="s9">Precious metals</p></td><td><p class="s9">Pure gold, hard gold from the Gaseous Phase (HV 150 – 250Vacuum Deposition), palladium, palladium-nickel, rhodium,</p><p class="s9">pure silver, hard silver =The term PVD (HV 130 – 160physical vapor deposition)</p></td></tr><tr><td><p class="s9">Non-precious metals</p></td><td><p class="s9">Copper, nickel, tindefines processes of metal, tin metal alloysand chemical compounds deposition in a vacuum by adding thermal and kinetic energy by particle bombardment. The main processes are the following four coating variations (</p></td></tr><tr><td><p classxr id="s9tab:Characteristics of the Most Important PVD Processes">Carrier materials</p></td><td><p class="s9">Copper, copper alloys, nickel, nickel alloys, iron, steel,</p><p class="s9">aluminum, aluminum alloys, composite materials</p><p class="s9">such as aluminum – silicon carbide</p></td></tr></table!--(Table 7.6-->):

*'''Quality criteria''' {| 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 components may occur|-|Arc vaporizingBesides others |Vaporizing of the following layer parameters are typically monitored target <br />plate inan electrical arc|10^{-process 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 materials possible through RF operation|-|Ion implantation|Combination of vapor <br />deposition and documented:sputtering|10^-1 Pa-1Pa|80eV-300eV|Very good adhesion from ion bombardment but also heating of the substrate material|}</figtable>

These quality tests are performed according to industry standards, internalstandards, and customer specifications respThe sputtering process has gained the economically most significant usage. Its process principle is illustrated in (<xr id="fig:Principle of sputtering"/><!--(Fig. 7.5)-->).

<figure id==== Electroplating "fig:Principle of sputtering">[[File:Principle of sputtering.jpg|right|thumb|Figure 1: Principle of Semi-finished Materials=sputtering Ar =Argon atoms; e =Electrons; M =Metal atoms]]</figure>The process for overall electroplating of stripsInitially, profiles, and wires a gas discharge is mostlyperformed on continuously operating reelignited in a low pressure (10^-to1 -reel equipment1 Pa) argon atmosphere. The processingsteps for 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 individual operations such as pre-cleaningtarget location, electroplatingthe deposition rate can be increased, rinsingare following making the same principles as those employed in parts electroplatingprocess more economical.

The overall coating is usually applied for silver plating and tin coating advantages of stripsthe PVD processes and wires. Compared to hard gold or palladium these deposits especially sputtering for electrical contact applications are ratherductile, ensuring that during following stamping and forming operations nocracks are generated in the electroplated layers.:

==== Selective Electroplating====Since precious metals are rather expensive it is necessary to perform theelectroplating most economically and coat only those areas that need *High purity of the deposit layers for functional purposes. This leads from overall plating to selectiveelectroplating of strip material in continuous reel-to-reel processes. Depending*Low thermal impact on the final parts design and the end application the processes can be appliedsubstrate to solid strip material as well as pre-stamped and formed continuous strips or*Almost unlimited coating materials utilizing wire-formed or machined pins which have been arranged as bandoliers*Low coating thickness tolerance attached to conductive metal strips.*Excellent adhesion (also by using additional intermediate layers)

The core part 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 selective precious metal electroplating is the actualelectroplating cell. In it the anode is arranged closely to the cathodic polarizedmaterial strip. Cathode screens or masks may be applied between the two tofocus the electrical field onto closely defined spots on the cathode stripnonconductive materials, as well as in semiconductors, opto-electronics, optics and medical technology applications.

Special high performance electrolytes There are used in selective electroplating 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 toreach short plating times diameter should be < 2:1). Profile wires, strips and allow a high flow rate 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 the electrolyte for a fastelectrolyte exchange in the actual coating areavacuum coated semi finished materials and parts"/>).

For a closely targeted electroplating <figure id="fig:Examples of limited precious metal coating of contactvacuum coated semi finished materials and parts">springs so-called brush-electroplating cells are employed ''(Fig. 7.1)''. The “brush”or “tampon” consists [[File:Examples of a roof shaped titanium metal part covered with a specialfelt-like material. The metal body has holes in defined spots through which theelectrolyte reaches the felt. In the same spots is also the anode consisting of afine platinum net. The pre-stamped vacuum coated semi finished materials and in the contact area pre-formed contactspring part is guided under a defined pressure over the electrolyte soaked feltmaterial and gets wetted with the electrolyteparts. This allows the metalelectroplating in highly selective spots. Fig. 7.1jpg|left|Figure 2:Brush (or “Tampon”) plating cell;1 Strip; 2 Anode; 3 Electrolyte feed;4 Felt covered cell For special applications, such as for example electronic component substrates,a dot shaped precious metal coating is required. This is achieved with two beltmasks running synchronous to the carrier material. One of these two masks haswindows which are open to the spot areas targeted for precious metal platingcoverage. '''Summary of the processes for selective electroplating''' *'''Immersion electroplating'''Overall or selective electroplating of both sides of solid strips or pre-stampedparts in strip form *'''Stripe electroplating'''Stripe electroplating on solid strips through wheel cells or using maskingtechniques *'''Selective electroplating'''One-sided selective coating Examples of solid, pre-stamped, or metallically belt-linkedstrips by brush plating *'''Spot electroplating'''Electroplating in spots of solid strips with guide holes or pre-stamped parts instrip form '''Typical examples of electroplated vacuum coated semi-finished materials'''(overall or selectively)and parts]]bild</figure>

<table border="1" cellspacing="0" styleclass="border-collapse:collapsetwocolortable"><tr><tdth rowspan="2"><p class="s8">Type of CoatingsSubstrate Materials</p></tdth><tdth colspan="12"><p class="s8">Coating ThicknessMaterials</p></tdth></tr><tr><tdth><p class="s8">Remarks</pspan>Ag</tdspan></trp><tr/th><tdth><p class="s8">Precious Metals</pspan>Au</tdspan><td/p><td/th></trth><trp><tdspan>Pt</span></p class="s8">Pure gold</th><th><p><p class="s8"span>Pd</span>Hard gold (AuCo 0.3)</p></tdth><tdth><p class="s8">0.1 - 3 µm<span>Cu</span></p></tdth><tdth><p class="s8">In special cases up to 10 µm<span>Ni</pspan></tdp></trth><trth><tdp><p class="s8"span>Ti</span>Palladium-nickel (PdNi20)</p></tdth><tdth><p class="s8">0.1 - 5 µm<span>Cr</span></p></tdth><tdth><p class="s8">Frequently with additional 0.2 µm AuCo 0.3<span>Mo</span></p></tdth></trth><trp><tdspan>W<p class="s8"/span>Silver</p></tdth><tdth><p class="s8">0.5 - 10 µm<span>Ai</span></p></tdth><tdth><p class="s8">In special cases up to 40 µm<span>Si</span></p></tdth></tr><tr><td><p class="s8">Non-precious MetalsPrecious metal / alloys</p></td><td/><td/p><span>[[File:K7-gef.png]]</trspan><tr><td><p class="s8">Nickel</p></td><td><p class="s8">0<span>[[File:K7-gef.5 - 4 µmpng]]</span></p></td><td><p class="s8">Diffusion barrier especially for gold layers<span>[[File:K7-gef.png]]</pspan></tdp></tr><trtd><td><p class="s8">Copper</pspan></[[File:K7-gef.png]]</span></p></td><td><p class="s8">1 <span>[[File:K7- 5 µmgef.png]]</span></p></td><td><p class="s8">Intermediate layer used in tinning of CuZn<span>[[File:K7-gef.png]]</pspan></tdp></tr><trtd><td><p class="s8">Tin, tin alloys</pspan><[[File:K7-gef.png]]</span></p></td><td><p class="s8">0<span>[[File:K7-gef.8 - 25 µmpng]]</span></p></td><td><p class="s8">materials<span>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</trspan></tablep> *'''Carrier Materials'''Copper, copper alloys, nickel, nickel alloys, stainless steel *'''Dimensions and Tolerances''' Bild  DimensionsCarrier thickness d= 0.1 - 1 mmCarrier width B= 6 - 130 mmDistance b </td> 2 mmCoating width a= 2 <td><p><span>[[File:K7- 30mmCoating thickness s = 0gef.2 - 5 μm(typical range)Distance from edge b png]]</span> 0.5 mmdepending on the carrier thicknessand the plating process *'''Tolerances'''Coating thickness approx</p></td><td><p><span>[[File:K7-gef. 10 %Coating thickness and position + 0,5 mm *'''Quality Criteria'''Mechanical properties and dimensional tolerances of the carrier materials followthe typical standards, i.e. DIN EN 1652 and 1654 for copper and copper alloys.Depending on the application the following parameters are tested andrecorded (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 resp. Main Articel: [[Electroplating (or Galvanic Deposition)| Electroplating (or Galvanic Deposition)]] png]]</span></p></td></tr><tr><td><p class===7.1"s8">NF metals / alloys</p></td><td><p><span>[[File:K7-gef.2 Electroless Plating=== ====7png]]</span></p></td><td><p><span>[[File:K7-gef.1.2png]]</span></p></td><td><p><span>[[File:K7-gef.1 Introduction====Electroless plating is defined as a coating process which is performed withoutthe use of an external current sourcepng]]</span></p></td><td><p><span>[[File:K7-gef. It allows a uniform metal coatingindependent of the geometrical shape of the parts to be coated. Because of thevery good dispersion capability 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 platingpng]]</span></p></td><td><p><span>[[File:processes in which the carrier material serves as a reduction agent (Immersionprocesses) and those in which a reduction agent is added to the electrolyte(Electroless processes)K7-gef. ====7png]]</span></p></td><td><p><span>[[File:K7-gef.1.2.2 Immersion Processes====The immersion processes are usually applied in the plating of the metals gold,silver, and tinpng]]</span></p></td><td><p><span>[[File:K7-gef. If the material to be coated is less precious, ipng]]</span></p></td><td><p><span>[[File:K7-gef.e. exhibits anegative standard potential against the metal ions in the surrounding solution, itgoes into solution releasing electrons while the more precious metal ions arereduced by absorbing electrons 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)''. Table 7.5: Immersion Gold Electrolytespng]]</span></p><table border="1" cellspacing="0" style="border-collapse:collapse"/td><td><trp><tdspan>[[File:K7-gef.png]]<p class="s8"/span>Type of Electrolyte</p></td><td><p class="s8">pH<span>[[File:K7-Rangegef.png]]</span></p></td><td><p class="s8">Coating Properties<span>[[File:K7-gef.png]]</span></p></td><td><p class="s8">Application Ranges<span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">Type of ElectrolyteFe alloys / stainless steel</p></td><td><p class="s8">pH-Range</pspan>[[File:K7-gef.png]]</td><td><p class="s8">Hardness</p><p class="s8"span>HV 0.025</p></td><td><p class="s8">Punity<span>[[File:K7-gef.png]]</span></p></td><td><p class="s8">Application Ranges<span>[[File:K7-gef.png]]</span></p></td></tr><tr><td><p class="s8">Immersion Gold electrolytes</pspan>[[File:K7-gef.png]]</tdspan><td/p><td/><td/><td/></trp><trspan>[[File:K7-gef.png]]<td/span></p class="s8">AUROL 4</ptd><p class="s8"td>AUROL 16</p><p class="s8"span>[[File:K7-gef.png]]</span>AUROL 20</p></td><td><p class="s8">3.8 <span>[[File:K7- 4gef.2png]]</pspan></p class="s8">5.8 - 6.2<//td><td><p><p class="s8"span>5.8 [[File:K7- 6gef.2png]]</pspan></p class="s8">5.8 - 6.2</ptd></td><tdp><p class="s8"span>60 [[File:K7- 80gef.png]]</pspan></p class="s8">60 - 80</ptd><p class="s8"td>60 - 80</p><p class="s8"span>60 [[File:K7- 80gef.png]]</span></p></td><td><p class="s8">99.99% Au</pspan>[[File:K7-gef.png]]</span></p class="s8">99.99% Au</ptd><p class="s8"td>99.99% Au</p><p class="s8"span>99[[File:K7-gef.99% Aupng]]</span></p></td></tr><tr><td><p class="s8">Thin gold layers on NiSpecial metals (Ti, Ni alloysMo,W)</p><p class="s8"/td><td>Fe and Fe alloys for PCB technology and technical applications</p><span>[[File:K7-leer.png]]</tdspan></trp></tabletd><td> ====7<p><span>[[File:K7-gef.1.2.3 Electroless Processes====The electroless metal plating with adding reduction agents to the electrolyte isbased on the oxidation of the reducing agent with release of electrons whichthen in turn reduce the metal ionspng]]</span></p></td><td><p><span>[[File:K7-gef. To achieve a controlled deposition from suchsolutions the metal deposition has to happen through the catalytic influence ofthe substrate surface. Otherwise a “wild” uncontrollable deposition would occur. In most casespalladium containing solutions are used for the activation which seed thesurfaces with palladium and act as catalysts in the copper and nickelelectrolytespng]]</span></p></td><td><p><span>[[File:K7-gef. The electrolytes contain besides the complex ion compounds of the metals tobe deposited also stabilizers, buffer and accelerator chemicals, and a suitablereduction agentpng]]</span></p></td><td><p><span>[[File:K7-gef. These electrolytes are usually operating at elevated temperatures (50° – 90°C).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 copper, nickel, and golddeposits. ====7.1.2.4 Electroless Deposition of Nickelpng]]</span></p></Gold==== Electroless deposited nickel coatings with an additional immersion layer of goldare seeing increased importance in the coating of printed circuit boards (PCBs).The process sequence is shown in ''(Fig. 7.2)'' using the example of theDODUCHEM process. Tabelle After the pretd><td><p><span>[[File:K7-cleaning (degreasing and etching) a palladium sulfate activator isused which activates the exposed copper surfaces on the printed circuit boardand thus facilitates the nickel depositiongef. The electroless working chemicalnickel electrolyte contains – besides other ingredients – Sodium-hypophosphite,which is reduced to phosphorus in a parallel occurring process andincorporated into the nickel deposit. At the temperature of 87 – 89°C a veryhomogeneous nickelpng]]</span></p></td><td><p><span>[[File:K7-phosphorus alloy layer with approxgef. 9 wt% P is depositedwith layer thicknesses png]]</span></p></td><td><p> 5 μm possible. During a consecutive processing stepa very thin and uniform layer (< 0span>[[File:K7-gef.1 μm) of gold is added in an immersionelectrolyte. This protects the electroless nickel layer against corrosion achievinga solderable and well bondable surface for thick or fine aluminum bond wires. It is possible to enhance this layer combination further by adding a immersionpalladium layer between the electroless nickel and the gold coating(DODUBOND process)png]]</span></p></td><td><p><span>[[File:K7-gef. This Pd layer acts as a diffusion barrier and allows theusage of this surface combination also for gold wire bonding. As an alternative, for gold wire bonding applications a thicker gold layer of 0png]]</span></p></td><td><p><span>[[File:K7-gef.2 –0.5 μm can be applied using an electroless process. Typical electrolytes work ata temperature of approxpng]]</span></p></td><td><p><span>[[File:K7-leer. 80°C with deposition rates of 0.3 – 0.4 μm per 30minutes. 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 ''(Figpng]]</span></p></td><td><p><span>[[File:K7-gef. 7.3png]]</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>, AlN)</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">Glasses (SiO<span class="s16">2</span>, 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, PPS)</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>

Fig. 7.3:Coating compositionof a printed circuit board withreductively enhanced gold ====7.1.2.5 Immersion Deposition of Tin====A tin coating by ion exchange is usually not possible since copper is the moreprecious metal. By adding thio-urea the electro-chemical potential of copper isreduced to a level (approx. 450 mV, significantly lower than tin) that allows theexchange reaction. Using a suitable electrolyte composition and enhancersolutions like with the DODUSTAN process ''(Fig. 7.4)'' tin coatings can beproduced that, even under usually unfavorable conditions of copperconcentrations of 7 g/l in the electrolyte, are well solderable. Fig. 7.4: Process flow for electroless tin deposition using the DODUSTAN process The immersion tin deposition is suitable for the production of a well solderablesurface on printed circuit boards and electronic components. It is also used asan etch resist against ammonia based solutions or as corrosion and oxidationprotection of copper surfaces. ==7.2 Coatings from the Gaseous Phase (Vacuum Deposition)==The term PVD (physical vapor deposition) defines processes of metal, metalalloys, and chemical compounds deposition in a vacuum by adding thermal andkinetic energy through particle bombardment. The main processes are thefollowing four coating variations ''(Table 7.6)'': *Vapor deposition *Sputtering (Cathode atomization)*Arc vaporizing *Ion implantation In all four processes the coating material is transported in its atomic form to thesubstrate and deposited on it as a thin layer (a few nm to approx. 10 μm) Table 7.6: Characteristics of the Most Important PVD Processes tabelle fehlt! The sputtering process has gained the economically most significant usage. Itsprocess principle is illustrated in ''(Fig. 7.5)''. Fig. 7.5: Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms Initially a gas discharge is ignited in a low pressure (10 – 1 Pa) argonatmosphere. The argon ions generated are accelerated in an electric field andimpact the target of material to be deposited with high energy. Caused by thisenergy atoms are released from the target material which condensate on theoppositely arranged anode (the substrate) and form a layer with high adhesionstrength. 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 electricalcontact applications are: *High purity of the deposit layers *Low thermal impact on the *Almost unlimited coating materials substrate*Low coating thickness tolerance *Excellent adhesion (also by using additional intermediate layers) Coatings produced by PVD processes are used for contact applications, forexample on miniature-profiles, in electrical engineering and for electroniccomponents, for solderability in joining processes, for metalizing of nonconductivematerials, 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 moreproblematic (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 coatedselectively by using masking fixtures that at the same time serve as holdingfixtures. *'''Examples of vacuum coated semi-finished materials and parts'''bild *'''Materials'''Selection of possible combinations of coating and substrate materials <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, Mo, W)</p></td><td><p><span>can be produced[[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">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>, AlN)</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">Glasses (SiO<span class="s16">2</span>, 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, PPS)</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>can be produced with intermediate layer

{| class="twocolortable" style="text-align: left; font-size: 12px;width:40%"|-!colspan="2" style="text-align:center"|'''Dimensions'''|-|Coating thickness: |10 nm - 15 μm|-|Coating 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 has

Coating thickness +&#177;10 - 30 %, depending on the thickness

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 resp.

==<!--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 chosen, considering 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. <xr id="tab:Comparison of different coating processes"/><!--Table 7.7--> gives 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 contact

The main differences between the <figtable id="tab:Comparison of different coating processes are found in the "><caption>'''<!--Table 7.7:-->Comparison of different coatingprocesses'''</caption> {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Process / Coating Properties!Mechanical Processes (Cladding)!Electroplating!Vaccum Deposition (Sputtering)|-|Coating materialmaterials |formabe metal and thickness. While mechanical cladding and sputtering allow thealloysuse of almost any alloy material|metals, electroplating processes are alloys only limited to |metalsand selected alloys such as for example high|-|Coating thickness|> 1μm|0.1 -carat gold alloys with approx. 10 μm <br />(in special cases up to .3100 μm)wt% Co or Ni|0. Electroplated and sputtered surface layers have a technologicaland economical upper thickness limit of about 10μm. While mechanical claddinghas a minimum thickness of 1 approx. 1 10 μm|-|Coating configuration|selectively, electroplating stamping edges not coated|all around and sputteringselectively<br />stamping edges coated|mostly selectivity|-|Adhesion|good|goodcan also be easily applied in |very thin layers down to the range good|-|Ductility|good|limited|good|-|Purity|good|inclusions of 0.1 μmforeign materials|very good|-|Porosity|good|good for > approx.1μm|good|-|Temperature stability|goodvery good|good|very good|-|Mechanical wear|little|very little|little|-|Environmental impact|little|significant|none|}</figtable>

The properties of main differences between the coatings coating processes are closely related to found in the coating processmaterials and thickness.Starting materials for While mechanical cladding and sputtering targets precious allow the use of almost any alloy material, electroplating processes are limited to metals and theirselected alloys which in the case of , such as for example high-carat gold alloys with up to .3 wt% Co or Ni. Electroplated and palladium based materials are vacuummelted sputtered surface layers have a technological and therefore exhibit economical upper thickness limit of about 10μm. While mechanical cladding has a very high purityminimum thickness of approx. During 1 μm, electroplating, dependingon and sputtering can also be easily applied in very thin layers down to the type range of electrolytes and the deposition parameters, some electrolytecomponents such as carbon and organic compounds are incorporated intothe precious metal coating0. Layers deposited from the gaseous phase howeverare very pure1 μm.

==7The properties of the coatings are closely related to the coating process.4 Hot (-Dipped) Tin Coated Strip Materials==During hot-dip tinning pre-treated strip Starting materials for cladding and sputtering targets precious metals and their alloys, which in the case of gold and palladium based materials , are coated with pure tin or tinalloys from vacuum melted and therefore exhibit a liquid solder metalvery high purity. During overall (or all-around) tinning electroplating, depending on thestripsthrough a liquid metal melt. For strip tinning rotating rolls are partiallyimmersed into a liquid tin melt type of electrolytes and transport the liquid onto the strip which isguided above them. Through special wiping deposition parameters, some electrolyte components such as carbon and gas blowing procedures organic compounds are incorporated into thedeposited tin layer can be held within tight tolerances. Hot tinning is performeddirectly onto the base substrate material without any pre-precious metal coating with eithercopper or nickel. Special cast-on processes or Layers deposited from the melting of solder foils ontothe carrier strip allow also the production of thicker solder layers(> 15 μm)gaseous phase however are very pure.

The main advantage of ==<!--7.4-->Hot (-Dipped) Tin Coated Strip Materials==During hot -dip tinning of copper and copper alloys as compared to, pre-treated strip materials are coated with pure tin electroplating is the formation of an inter-metallic copper-or tin phase alloys from a liquid solder metal. During overall (Cu₃Sn,Cu₆ Sn₅or all-around) at tinning the boundary between strips through a liquid metal melt. For strip tinning, rotating rolls are partially immersed into a liquid tin melt and transport the carrier material and liquid onto the tin layer. This thin(0.3 – 0.5 μm) intermediate layerstrip, which is formed during the thermal tinningprocessguided above them. Through special wiping and gas blowing procedures, is rather hard and reduces in connectors the frictional force andmechanical weardeposited tin layer can be held within tight tolerances. Tin coatings produced by hot Hot tinning have a good adhesion tois performed directly onto the base substrate material and do not tend to tin whisker formationwithout any pre-coating with either copper or nickel. Special cast-on processes or the melting of solder foils onto the carrier strip, also allows the production of thicker solder layers ( > 15 μm).

A special process The main advantage of hot tinning of copper and copper alloys, compared to tin electroplating, is the “Reflow” process. After depositing a formation of an inter-metallic copper-tincoating by electroplating 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 short-time melted rather hard and reduces the frictional force and mechanical wear in a continuous processconnectors.The properties of these reflow tin Tin coatings are comparable to those created produced byconventional hot tinninghave a good adhesion to the substrate material and do not tend to tin whisker formation.

Besides overall A special process of hot tinning is the “Reflow” process. After depositing a tin coating of strip material by electroplating, the hot tinning can also be applied layer is short-time melted inthe form of single or multiple stripes on both sides of a continuous substrateprocess.stripThe 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'''bild"/>).

Coating materials: Pure tin, tin alloys<br>Substrate materials: Cu, CuZn, CuNiZn, CuSn, CuBe and others<br />

{| class="twocolortable" style="text-align: left; font-size: 12px;width:40%"|-|Width of tinning: > |&#8805; 3 + &#177; 1 mm|-|Thickness of tinning: |1 - 15 μm|-|Tolerances (thickness): + |&#177; 1 - +&#177; 3 μm depending on tin thickness|}

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.

==<!--7.5 -->Contact Lubricants==By 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.

Solid lubricants include for example 0.05 – 0.2 μm thin hard gold layers , whichare added as surface layers on top of the actual contact material. Among the various contact lubricants offered on the market contact lubricationoils have shown performance advantages. They are mostly synthetic, chemically inert, and silicone-free oils such as for example the DODUCONTAcontact lubricants which differ in their chemical composition and viscosity. For sliding contact systems with contact forces < 50 cN and higher slidingspeeds oils with a lower viscosity (<50 mPa·s) are preferential. For applicationswith higher contact forces and operating at higher temperatures contact oilswith a higher viscosity are advantageous. Contact oils are mainly suited forapplications at low current loads. At higher loads and in situations wherecontact separation occurs during the sliding operation thermal decompositionmay be initiated which causes the lubricating properties to be lost.

Most compatible with plastics are Among the various contact oil varieties B5lubricants offered on the market, B12Kcontact lubrication oils have shown performance advantages. They are mostly synthetic, chemically inert and B25,silicone-free oils which also over longer operating times do not lead to tension stress corrosiondiffer in their chemical composition and viscosity.

For the optimum lubrication only sliding contact systems with contact forces < 50 cN and higher sliding speeds, oils with a very thin layer of lower viscosity (< 50 mPa·s) are preferential. For applications with higher contact oil is requiredforces and operating at higher temperatures, contact oils with a higher viscosity are advantageous.Therefore it is Contact oils are mainly suited for example recommended to dilute the oil applications at low current loads. At higher loads and in iso-propylenealcoholsituations where contact separation occurs during the application sliding operation, thermal decomposition may be initiated, which causes the lubricating properties to contact parts. After evaporation of the alcohola thin and uniform layer of lubricant is retained on the contact surfacesbe lost.

*'''Properties of the Synthetic DODUCONTA Contact Lubricants''' <table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s8">Lubricant</p></td><td><p class="s8">DODUCONTA</p></td></tr><tr><td><p class="s8">Lubricant</p></td><td><p class="s8">B5</p></td><td><p class="s8">B9</p></td><td><p class="s8">B10</p></td><td><p class="s8">B12K</p></td><td><p class="s8">B25</p></td></tr><tr><td><p class="s8">Contact force</p></td><td><p class="s8">&gt;1N</p></td><td><p class="s8">0.1 !- 2N</p></td><td><p class="s8">&lt; 0.2N</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">17.9</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 10<span class="s18">10</span></p></td><td><p class="s8">10<span class="s18">10</span></p></td><td><p class="s8">6 x 10<span class="s18">9</span></p></td><td><p class="s8">5 x 10<span class="s18">8</span></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><tr><td/><td><p class="s8">220</p></td><td/><td/></tr></table>  *'''Applications of the Synthetic DODUCONTA Contact Lubricants''' <table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s8">Lubricant</p></td><td><p class="s8">Applications</p></td></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 silversurface in sulfur containing environments , can be significantly eliminated bycoating them with an additional protective film layer (Passivation layer). Forelectrical contact use , such thin layers should be chemically inert andsufficiently conductive, or be 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]]</figure>The passivation process SILVERBRITE W ATPS is a water-based tarnishpreventer for silver(<xr id="fig:Typical process flow for the SILVERBRITE W ATPS process"/>). It is free of chromium(VI) compounds and solvents. Thepassivating layer is applied by immersion , which creates a transparent organicprotective film which barely changes the appearance and only slightlyincreases the good electrical properties such as for example the contactresistance. The good solderability and bond properties of silver are notnegatively affected. Because of its chemical composition , this protective layerhas some lubricating properties which reduce the insertion and withdrawalforces of connectors noticeably. Fig. 7.7: Typical process flow for the SILVERBRITE W ATPS process