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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|<sup>*)</sup>]] |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.
==Coatings from the Liquid Phase==
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.
=== Electroplating (or Galvanic Deposition)===
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.
===== 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:-->Electroless Plating===
*'''Rhodium electrolytes''' Rhodium deposits are extremely hard Vapor deposition *Sputtering (HV 700 – 1000Cathode atomization) and wear resistant. They also excel in light reflection. Both properties 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 of the light whitish deposits with high corrosion resistance.*Arc vaporizing *Ion implantation
<table borderfigtable id="1" cellspacing="0" style="border-collapsetab:collapse"><tr><td><p class="s8">AUROMET TN</p></td><td><p class="s8">3.2 - 4.2</p></td><td><p class="s8">ca. 70</p></td><td><p class=Characteristics of the Most Important PVD Processes"s8">99.99% Au</p></td><tdcaption>'''<p class="s8">Base!-deposits</p></td></tr><tr><td><p class="s8">AUROMET XPH</p></td><td><p class="s8">0.3 - 0Table 7.6</p></td><td><p class="s8">160 - 180</p></td><td><p class="s8">99.8% Au</p></td><td><p class="s8">Base-deposits for stainless steel etc.</p></td></tr><tr><td><p class="s8">DODUREX COC</p></td><td><p class="s8">4.6 - 4.9</p></td><td><p class="s8">160 - 180</p></td><td><p class="s8">99.6% Au</p></td><td><p class="s8">Printed circuit boards, connectors, contact parts, etc.; hard gold coatings for rack and barrel plating</p></td></tr><tr><td><p class="s8">DODUREX HS 100</p></td><td><p class="s8">4.3 - 4.6</p></td><td><p class="s8">160 - 180</p></td><td><p class="s8">99.6% Au</p></td><td><p class="s8">High speed process for connectors and</p><p class="s8">PCB plating</p></td></tr><tr><td><p class="s8">PURAMET 202</p><p class="s8">PURAMET 402</p></td><td><p class="s8">5.5 :- 6.5</p><p class="s8">7.0 - 7.5</p></td><td><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></td><td><p class="s8">High purity gold coatings for electrical</p><p class="s8">and electronic parts incl. semi conductors and PCBs; for demanding requirement on bonding properties</p></td></tr>Characteristics of the Most Important PVD Processes'''</tablecaption>
{| class="twocolortable" style==== Non"text-align: left; font-size: 12px"|-Precious Metal Electrolytes=====The most important non!Process!Principle!Process Gas Pressure!Particle Energy!Remarks|-precious metals that are deposited by electroplatingare: Copper, nickel, tin, and zinc and their alloys. The |Vapor deposition is performed |Vaporizing ina crucible <br />(electron beam or resistance heating)|10<sup>-3</sup> Pa|< 2eV|Separation of alloy components may occur|-|Arc vaporizing|Vaporizing of the form target <br />plate in an electrical arc|10<sup>-1</sup> Pa-1Pa|80eV-300eV|Very good adhesion due to ion bombardement|-|Sputtering|Atomizing of pure metals with different electrolytes used ''the target plate<br />(Table 7.4cathode).''in a gas discharge|10<sup>-1</sup> Pa-1Pa|10eV-100eV|Sputtering of non-conductive materials possible through RF operation|-|Ion implantation|Combination of vapor <br />deposition and sputtering|10<sup>-1</sup> Pa-1Pa|80eV-300eV|Very good adhesion from ion bombardment but also heating of the substrate material|}</figtable>
*'''Bronze electrolytes''' Bronze coatings – in white or yellow color tones – are used either as an allergy free nickel replacement or as a surface layer for decorative purposes. For technical applications High purity of the bronze deposit layers are utilized for their good corrosion resistance and good brazing and soldering properties. *Low thermal impact on the substrate *Almost unlimited coating materials *Low coating thickness tolerance *Excellent adhesion (also by using additional intermediate layers)
<br style="clear:both;"/>
*'''Materials'''
Selection of possible combinations of coating and substrate materials
<table borderclass="1twocolortable" cellspacing><tr><th rowspan="02" style><p class="border-collapse:collapses8">Substrate Materials</p><tr/th><tdth colspan="12"><p class="s9s8">CoatingsCoating Materials</p></tdth></tr><tr><tdth><p class="s9">Precious metals<span>Ag</span></p></tdth><tdth><p class="s9">Pure gold, hard gold (HV 150 – 250), palladium, palladium-nickel, rhodium,<span>Au</pspan></p class="s9">pure silver, hard silver (HV 130 – 160)<//th><th><p><span>Pt</tdspan></trp><tr/th><tdth><p class="s9">Non-precious metals<span>Pd</pspan></tdp><td/th><th><p class="s9">Copper, nickel, tin, tin alloys<span>Cu</span></p></tdth></trth><trp><tdspan>Ni<p class="s9"/span>Carrier materials</p></tdth><tdth><p class="s9">Copper, copper alloys, nickel, nickel alloys, iron, steel,<span>Ti</pspan></p class="s9">aluminum, aluminum alloys, composite materials</pth><p class="s9"th>such as aluminum – silicon carbide</p><span>Cr</span></p></tdth><th><p><span>Mo</trspan></tablep></th><th><p><span>W</span></p></th><th><p><span>Ai</span></p></th><th><p><span>Si</span></p></th></tr> *'''Coating thickness''' Precious metals: 0.2 – 5 μm (typical layer thicknesses; for Ag also up to 25 μm)Non-precious metals: Up to approx. 20 μmTolerances: Strongly varying depending on the geometrical shape ofparts (up to 50% at a defined measuring spot).It is recommended to specify a minimum value for thecoating thickness at a defined measuring spot als Bild? *'''Quality criteria''' Besides others the following layer parameters are typically monitored in-process and documented: *Coating thickness *Solderability*Adhesion strength *Bonding property*Porosity Contact *resistance These quality tests are performed according to industry standards, internalstandards, and customer specifications resp. ==<tr><td><p class== Electroplating of Semi"s8">Precious metal / alloys</p></td><td><p><span>[[File:K7-finished Materials====The process for overall electroplating of strips, profiles, and wires is mostlyperformed on continuously operating reel-togef.png]]</span></p></td><td><p><span>[[File:K7-reel equipmentgef. The processingsteps for the individual operations such as prepng]]</span></p></td><td><p><span>[[File:K7-cleaning, electroplating, rinsingare following the same principles as those employed in parts electroplatinggef. The overall coating is usually applied for silver plating and tin coating of stripsand wires. Compared to hard gold or palladium these deposits are ratherductile, ensuring that during following stamping and forming operations nocracks are generated in the electroplated layerspng]]</span></p></td><td><p><span>[[File:K7-gef. ==== Selective Electroplating====Since precious metals are rather expensive it is necessary to perform theelectroplating most economically and coat only those areas that need the layersfor functional purposes. This leads from overall plating to selectiveelectroplating of strip material in continuous reel-topng]]</span></p></td><td><p><span>[[File:K7-reel processesgef. 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 wirepng]]</span></p></td><td><p><span>[[File:K7-formed or machined pins which have been arranged as bandoliersattached to conductive metal stripsgef. The core part 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 strip. Special high performance electrolytes are used in selective electroplating toreach short plating times and allow a high flow rate of the electrolyte for a fastelectrolyte exchange in the actual coating area. For a closely targeted electroplating of limited precious metal coating of contactsprings so-called brushpng]]</span></p></td><td><p><span>[[File:K7-electroplating cells are employed ''(Figgef. 7.1)''. The “brush”or “tampon” consists of a roof shaped titanium metal part covered with a specialfeltpng]]</span></p></td><td><p><span>[[File:K7-like materialgef. 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 and in the contact area prepng]]</span></p></td><td><p><span>[[File:K7-formed contactspring part is guided under a defined pressure over the electrolyte soaked feltmaterial and gets wetted with the electrolytegef. This allows the metalelectroplating in highly selective spots. Fig. 7.1png]]</span></p></td><td><p><span>[[File: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 requiredK7-gef. 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 platingcoveragepng]]</span></p></td><td><p><span>[[File:K7-gef. '''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'''Onepng]]</span></p></td><td><p><span>[[File:K7-sided selective coating 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 semi-finished materials'''(overall or selectively)bild *'''Materials''' <table border="1" cellspacing="0" style="border-collapse:collapse"gef.png]]</span></p></td></tr><tr><td><p class="s8">Type of CoatingsNF metals / alloys</p></td><td><p class="s8">Coating Thickness<span>[[File:K7-gef.png]]</span></p></td><td><p class="s8">Remarks</pspan>[[File:K7-gef.png]]</tdspan></trp><tr/td><td><p class="s8">Precious Metals</pspan>[[File:K7-gef.png]]</tdspan><td/p></td/></trtd><trp><tdspan>[[File:K7-gef.png]]</span></p class="s8">Pure gold</td><td><p><p class="s8"span>Hard gold (AuCo 0[[File:K7-gef.3)png]]</span></p></td><td><p class="s8">0<span>[[File:K7-gef.1 - 3 µmpng]]</span></p></td><td><p class="s8">In special cases up to 10 µm</pspan>[[File:K7-gef.png]]</tdspan></trp><tr/td><td><p class="s8">Palladium<span>[[File:K7-nickel (PdNi20)gef.png]]</span></p></td><td><p class="s8">0<span>[[File:K7-gef.1 - 5 µmpng]]</span></p></td><td><p class="s8">Frequently with additional 0<span>[[File:K7-gef.2 µm AuCo 0.3png]]</span></p></td></trtd><trp><tdspan>[[File:K7-gef.png]]<p class="s8"/span>Silver</p></td><td><p class="s8">0<span>[[File:K7-gef.5 - 10 µmpng]]</p></td><td><p class="s8"span>In special cases up to 40 µm</p></td></tr><tr><td><p class="s8">Non-precious MetalsFe alloys / stainless steel</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]]</span></p></td></trtd><trp><tdspan>[[File:K7-gef.png]]<p class="s8"/span>Copper</p></td><td><p class="s8">1 - 5 µm</pspan>[[File:K7-gef.png]]</span></p></td><td><p class="s8">Intermediate layer used in tinning of CuZn</pspan>[[File:K7-gef.png]]</tdspan></trp><tr/td><td><p class="s8">Tin, tin alloys<span>[[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</pspan>[[File:K7-gef.png]]</span></p></td><td><p><span>[[File:K7-gef.png]]</span></trp></tabletd> *'''Carrier Materials'''Copper, copper alloys, nickel, nickel alloys, stainless steel *'''Dimensions and Tolerances''' Bild DimensionsCarrier thickness d= 0<td><p><span>[[File:K7-gef.1 - 1 mmCarrier width B= 6 - 130 mmDistance b png]]</span> 2 mmCoating width a= 2 </p></td><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. 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 </p></td></tr><tr><td><p class="s8">Special metals (see also: Electroplating of parts): *Coating thickness *Solderability*Adhesion strength *Bonding property *Porosity *Contact resistance These quality tests are performed according to industry standardsTi, internalstandardsMo, and customer specifications resp. ===7W)</p></td><td><p><span>[[File:K7-leer.1.2 Electroless Plating=== ====7png]]</span></p></td><td><p><span>[[File:K7-gef.1.2.1 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, i.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 7png]]</span></p></td><td><p><span>[[File:K7-gef.5: Immersion Gold Electrolytespng]]<table border="1" cellspacing="0" style="border-collapse:collapse"/span><tr/p></td><p class="s8"td>Type of Electrolyte</p></tdspan>[[File:K7-gef.png]]<td/span><p class="s8">pH-Range</p></td><td><p class="s8">Coating Properties<span>[[File:K7-gef.png]]</span></p></td><td><p class="s8">Application Ranges</pspan><[[File:K7-gef.png]]</tdspan></trp><tr/td><td><p class="s8">Type of Electrolyte<span>[[File:K7-leer.png]]</span></p></td><td><p class="s8">pH<span>[[File:K7-Rangegef.png]]</pspan></p></td><td/tr><p class="s8"tr>Hardness</ptd><p class="s8">HV 0.025Carbide steels (WC-Co)</p></td><td><p class="s8">Punity</pspan>[[File:K7-leer.png]]</tdspan><td><p class="s8">Application Ranges</p></td></trtd><trp><tdspan>[[File:K7-gef.png]]<p class="s8"/span>Immersion Gold electrolytes</p></td><td/><td/p><tdspan>[[File:K7-gef.png]]</span><td/p></trtd><trtd><tdp><p class="s8"span>AUROL 4[[File:K7-gef.png]]</pspan></p class="s8">AUROL 16</ptd><td><p class="s8">AUROL 20<span>[[File:K7-gef.png]]</span></p></td><td><p class="s8">3.8 <span>[[File:K7- 4gef.2png]]</span></p><p class="s8"/td><td>5.8 - 6.2</p><p class="s8"span>5.8 [[File:K7- 6gef.2png]]</pspan></p class="s8">5.8 </td><td><p><span>[[File:K7- 6gef.2png]]</span></p></td><td><p class="s8">60 <span>[[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<span>[[File:K7-leer.99% Aupng]]</pspan></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]]</pspan></p></td></tr><tr><td><p class="s8">Thin gold layers on Ni, Ni alloys,Ceramics (Al<span class="s16">2</pspan>O<p span class="s8s16">Fe and Fe alloys for PCB technology and technical applications3</pspan>, AlN)</p></td><td><p><span>[[File:K7-leer.png]]</span></trp></tabletd><td> ====7<p><span>[[File:K7-leer.1png]]</span></p></td><td><p><span>[[File:K7-gef.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 surfacepng]]</span></p></td><td><p><span>[[File:K7-gef. 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 agent. These electrolytes are usually operating at elevated temperatures (50° – 90°C)png]]</span></p></td><td><p><span>[[File:K7-gef.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. ====7png]]</span></p></td><td><p><span>[[File:K7-gef.1.2.4 Electroless Deposition of Nickelpng]]</span></Gold==== Electroless deposited nickel coatings with an additional immersion layer of goldare seeing increased importance in the coating of printed circuit boards (PCBs)p></td><td><p><span>[[File:K7-gef.The process sequence is shown in ''(Fig. 7.2)'' using the example of theDODUCHEM process. Tabelle 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 deposition. The electroless working chemicalnickel electrolyte contains – besides other ingredients – Sodiumpng]]</span></p></td><td><p><span>[[File:K7-hypophosphite,which is reduced to phosphorus in a parallel occurring process andincorporated into the nickel depositgef. At the temperature of 87 – 89°C a veryhomogeneous nickelpng]]</span></p></td><td><p><span>[[File:K7-phosphorus alloy layer with approxleer. 9 wt% P is depositedwith layer thicknesses png]]</span> 5 μm possible. During a consecutive processing stepa very thin and uniform layer (< 0.1 μm) of gold is added in an immersionelectrolyte/p></td><td><p><span>[[File:K7-gef. 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). 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 0.2 –0.5 μm can be applied using an electroless process. Typical electrolytes work ata temperature of approx. 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 ''png]]</span></p></td></tr><tr><td><p class="s8">Glasses (Fig. 7.3SiO<span class="s16">2</span>, CaF)''. Fig. 7.3:Coating compositionof a printed circuit board withreductively enhanced gold ====7</p></td><td><p><span>[[File:K7-leer.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 electropng]]</span></p></td><td><p><span>[[File:K7-chemical potential of copper isreduced to a level (approxleer. 450 mV, significantly lower than tin) that allows theexchange reactionpng]]</span></p></td><td><p><span>[[File:K7-gef. 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 gpng]]</l in the electrolyte, are well solderable. Fig. 7.4span></p></td><td><p><span>[[File: 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 componentsK7-gef. It is also used asan etch resist against ammonia based solutions or as corrosion and oxidationprotection of copper surfaces. ==7png]]</span></p></td><td><p><span>[[File:K7-gef.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 bombardmentpng]]</span></p></td><td><p><span>[[File:K7-gef. 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 approxpng]]</span></p></td><td><p><span>[[File:K7-gef. 10 μm) Table 7.6png]]</span></p></td><td><p><span>[[File: Characteristics of the Most Important PVD Processes tabelle fehlt! The sputtering process has gained the economically most significant usageK7-gef. Itsprocess principle is illustrated in ''(Fig. 7.5)''. Fig. 7.5png]]</span></p></td><td><p><span>[[File: Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms Initially a gas discharge is ignited in a low pressure (10 – 1 Pa) argonatmosphereK7-gef. 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 adhesionstrengthpng]]</span></p></td><td><p><span>[[File:K7-gef. 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 arepng]]</span></p></td><td><p><span>[[File: *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 miniatureK7-profiles, in electrical engineering and for electroniccomponents, for solderability in joining processes, for metalizing of nonconductivematerials, as well as in semiconductors, optoleer.png]]</span></p></td><td><p><span>[[File:K7-electronics, optics,and medical technology applicationsgef.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>
*'''Dimensions'''
{| 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
limitations.
*'''Tolerances'''
Coating thickness +±10 - 30 %, 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 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
applications.
The main advantage properties of hot tinning of copper the coatings are closely related to the coating process. Starting materials for cladding and sputtering targets precious metals and copper their alloys as compared totin electroplating is , which in the formation case of an inter-metallic copper-tin phase (Cu<sub>3</sub>Sngold and palladium based materials,Cu<sub>6</sub> Sn<sub>5</sub>) at the boundary between the carrier material are vacuum melted and the tin layertherefore exhibit a very high purity. This thin(0.3 – 0.5 μm) intermediate layerDuring electroplating, which is formed during depending on the type of electrolytes and the thermal tinningprocessdeposition parameters, is rather hard some electrolyte components such as carbon and reduces in connectors organic compounds are incorporated into the frictional force andmechanical wearprecious metal coating. Tin coatings produced by hot tinning have a good adhesion toLayers deposited from the substrate material and do not tend to tin whisker formationgaseous phase however are very pure.
Besides overall tin coating of strip material, the hot tinning can also be applied in the form of single or multiple stripes on both sides of a continuous substrate strip (<xr id="fig:Typical examples of hot tinned strip materials"/>).
<figure id="fig:Typical examples of hot tinned strip materials">
[[File:Typical examples of hot tinned strip materials.jpg|left|Figure 3: Typical examples of hot tinned strip materials]]
<br style="clear:both;"/>
</figure>
<br style="clear:both;"/>
*'''Materials'''
Coating materials: Pure tin, tin alloys<br>Substrate materials: Cu, CuZn, CuNiZn, CuSn, CuBe and others<br />
*'''Dimensions and Tolerances'''
{| class="twocolortable" style="text-align: left; font-size: 12px;width:40%"|-|Width of tinning: > |≥ 3 + ± 1 mm|-|Thickness of tinning: |1 - 15 μm|-|Tolerances (thickness): + |± 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 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.
Contact lubricants have to fulfill a multitude of technical requirements:
*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
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.
==<!--7.6-->Passivation of Silver Surfaces==The formation of silver sulfide during the shelf life of components with silver surface in sulfur containing environments, can be significantly eliminated by coating them with an additional protective film layer (Passivation layer). For electrical contact use, such thin layers should be chemically inert and sufficiently conductive, otherwise they are easily broken by the optimum lubrication only a very thin layer of applied contact oil is requiredforce.Therefore it is <figure id="fig:Typical process flow for example recommended to dilute the oil in iso-propylenealcoholSILVERBRITE W ATPS process">during [[File:Typical process flow for the application to contact partsSILVERBRITE W ATPS process. After evaporation of jpg|right|thumb|Figure 4: Typical process flow for the alcoholSILVERBRITE W ATPS process]]</figure>The passivation process SILVERBRITE W ATPS is a thin 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 uniform solvents. The passivating layer of lubricant is retained on applied by immersion, which creates a transparent organic protective film which barely changes the appearance and only slightlyincreases the good electrical properties such as for example the contact surfacesresistance. The good solderability and bond properties of silver are notnegatively affected. Because of its chemical composition, this protective layer has some lubricating properties which reduce the insertion and withdrawal forces of connectors noticeably.
Vinaricky, E. (Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
das Korrosions- und Kontaktverhalten von Ag – Beschichtungen in
schwefelhaltiger Umgebung. VDE – Fachbericht 65 (2009) 51 – 58
[[de:Beschichtungsverfahren]]