210
edits
Changes
temp edit
Neben der Herstellung der Kontaktwerkstoffe aus der festen Phase, z.B. auf
schmelz- oder pulvermetallurgischem Wege, bietet sich die Herstellung über die
flüssige und gasförmige Phase vor allem dann an, wenn dünne Schichten im
μm-Bereich benötigt werden, die nach den üblichen Plattiertechniken nicht
wirtschaftlich herstellbar sind <xr id="tab:Overview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications"/><!--(Tab. 7.1)-->. Derartige Schichten erfüllen, abhängig
von ihrer chemischen Zusammensetzung und Dicke, unterschiedliche
Anforderungen. Sie dienen z.B. als Korrosions- und Verschleißschutz oder
übernehmen die Funktion einer Kontaktschicht, an die bestimmte technische
Anforderungen gestellt werden. Daneben stellen sie für dekorative Zwecke eine
optisch ansprechende und verschleißfeste Oberflächenschicht dar.
<figtable id="tab:Overview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications">
<caption>'''<!--Table 7.1:-->Übersicht über einige wichtige Eigenschaften galvanisch abgeschiedener Schichten und die jeweiligen Anwendungen'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
|-
!Eigenschaften
!Anwendungszweck
!Anwendungsbeispiele
|-
|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">*) Koerzitivkraft = Kraft, mit der ein Stoff versucht, die einmal angenommene Magnetisierung zu behalten</div>
Um den mechanischen Verschleiß bei dünnen Schichten zu verringern,
kommen bei Gleit- und Steckkontakten Schmiermittel meist in flüssiger Form
zum Einsatz. Bei Silber-Kontakten bieten sog. Passivierungsschichten einen
Schutz gegenüber Silbersulfidbildung.
==Beschichtung über die flüssige Phase==
Für dünne, über die flüssige Phase erzeugte Schichten bieten sich zwei Herstellungsverfahren
an. Sie unterscheiden sich dadurch, dass die metallische
Abscheidung mit oder ohne äußere Stromquelle erfolgt. Im ersten Fall handelt
es sich um eine galvanische Beschichtung, im zweiten um eine chemische
Beschichtung.
===Galvanische Beschichtung===
Zur galvanischen Abscheidung von Metallen, insbesondere Edelmetallen,
werden wässrige Lösungen (Elektrolyte) verwendet, die die abzuscheidenden
Metalle in Form von Ionen (z.B. gelöste Metallsalze) enthalten. Unter dem
Einfluss eines elektrischen Feldes zwischen der Anode und dem kathodisch
geschalteten Beschichtungsgut gelangen positiv geladene Metallionen zur
Kathode, wo sie ihre Ladung abgeben und sich als Metall auf der Oberfläche
abscheiden.
Je nach Einsatz, in der Elektrotechnik und Elektronik oder für dekorative
Zwecke, kommen unterschiedliche galvanische Bäder (Elektrolyte) zur
Anwendung. Die für die Edelmetallbeschichtung eingesetzten Galvanisieranlagen
und der Umfang ihrer Ausrüstung werden durch den vorgesehenen
technologischen Prozess bestimmt.
Die galvanischen Arbeitsverfahren erstrecken sich nicht nur auf den Vorgang
der reinen elektrochemischen Metallabscheidung, sondern umfassen auch die
Vor- und Nachbehandlung der zu beschichtenden Ware. Wichtigste Voraussetzung
für die Herstellung eines festhaftenden Überzuges ist eine metallisch
blanke, d.h. fett- und oxidfreie Oberfläche des zu veredelnden Werkstückes.
Hierfür gibt es verschiedene Vorbehandlungsverfahren, die auf den Oberflächenzustand
und die Eigenschaften des Werkstoffes abgestimmt sind.
In den folgenden Abschnitten werden galvanische Bäder - Edelmetall- und
Unedelmetallbäder - sowie die wichtigsten Galvanisierverfahren beschrieben.
siehe Artikel: [[Galvanische_Beschichtung| Galvanische Beschichtung]]
===<!--7.1.2-->Stromlose Beschichtung===
Unter stromloser Metallabscheidung versteht man Beschichtungsverfahren, die
ohne Anwendung einer äußeren Stromquelle ablaufen. Sie ermöglichen eine
gleichmäßige Metallbeschichtung unabhängig von der geometrischen Form der
zu beschichtenden Teile. Aufgrund der sehr guten Streufähigkeit dieser Bäder
lassen sich z.B. auch Innenseiten von Bohrungen beschichten.
Prinzipiell können zwei Verfahren der außenstromlosen Metallabscheidung
unterschieden werden: Verfahren, bei denen das zu beschichtende Substratmaterial
als Reduktionsmittel dient (Austauschverfahren), und solche, bei denen
dem Elektrolyt ein Reduktionsmittel zugesetzt wird (Reduktionsverfahren).
siehe Artikel: [[Stromlose_Beschichtung| Stromlose Beschichtung]]
==<!--7.2-->Beschichtung über die Gasphase (Vakuumbeschichtung)==
Unter der Bezeichnung PVD (physical vapor deposition) werden Beschichtungsverfahren
zusammengefasst, bei denen die Abscheidung von Metallen, Legierungen
sowie chemischen Verbindungen im Vakuum durch Zufuhr thermischer
oder kinetischer Energie mittels Teilchenbeschuss erfolgt. Dabei unterscheidet
man hauptsächlich vier Beschichtungsvarianten <xr id="tab:Characteristics of the Most Important PVD Processes"/><!--(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 the substrate and deposited on it as a thin layer (a few nm to approx. 10 μm)
<figtable id="tab:Characteristics of the Most Important PVD Processes">
<caption>'''<!--Table 7.6:-->Characteristics of the Most Important PVD Processes'''</caption>
{| 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<sup>-3</sup> Pa
|< 2eV
|Separation of alloy components may occur
|-
|Arc vaporizing
|Vaporizing of the 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 the target plate<br />(cathode) 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>
The sputtering process has gained the economically most significant usage. Its process principle is illustrated in <xr id="fig:Principle of sputtering"/><!--(Fig. 7.5)-->.
<figure id="fig:Principle of sputtering">
[[File:Principle of sputtering.jpg|right|thumb|Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms]]
</figure>
Initially a gas discharge is ignited in a low pressure (10<sup>-1</sup> -1 Pa) argon atmosphere. The argon ions generated are accelerated in an electric field and impact the target of material to be deposited with high energy. Caused by this energy atoms are released from the target material which condensate on the oppositely arranged anode (the substrate) and form a layer with high adhesion strength. Through an overlapping magnetic field at the target location the deposition rate can be increased, making the process more economical.
The advantages of the PVD processes and especially sputtering for electrical contact applications are:
*High purity of the deposit layers
*Low thermal impact on the substrate
*Almost unlimited coating materials
*Low coating thickness tolerance
*Excellent adhesion (also by using additional intermediate layers)
Coatings produced by PVD processes are used for contact applications, for example on miniature-profiles, in electrical engineering and for electronic components, for solderability in joining processes, for metalizing of nonconductive materials, as well as in semiconductors, opto-electronics, optics, and medical technology applications.
There are few limitations regarding the geometrical shape of substrate parts. Only the interior coating of drilled holes and small diameter tubing can be more problematic (ratio of depth to diameter should be < 2:1). Profile wires, strips, and foils can be coated from one side or both; formed parts can be coated selectively by using masking fixtures that at the same time serve as holding fixtures.
*'''Examples of vacuum coated semi-finished materials and parts'''
[[File:Examples of vacuum coated semi finished materials and parts.jpg|left|Examples of vacuum coated semi finished materials and parts]]
<br style="clear:both;"/>
*'''Materials'''
Selection of possible combinations of coating and substrate materials
<table class="twocolortable">
<tr><th rowspan="2"><p class="s8">Substrate Materials</p></th><th colspan="12"><p class="s8">Coating Materials</p></th></tr>
<tr><th><p><span>Ag</span></p></th><th><p><span>Au</span></p></th><th><p><span>Pt</span></p></th><th><p><span>Pd</span></p></th><th><p><span>Cu</span></p></th><th><p><span>Ni</span></p></th><th><p><span>Ti</span></p></th><th><p><span>Cr</span></p></th><th><p><span>Mo</span></p></th><th><p><span>W</span></p></th><th><p><span>Ai</span></p></th><th><p><span>Si</span></p></th></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>[[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>
[[File:K7-gef.png]] can be produced
[[File:K7-leer.png]] can be produced with intermediate layer
*'''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 few restrictions. 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, internal standards, and customer specifications resp.
==<!--7.3-->Comparison of Deposition Processes==
The individual deposition processes have in part different performance characteristics. For each end application the optimal process has to be chosen considering all technical and economical factors. The main selection criteria should be based on the electrical and mechanical requirements for the contact layer and on the design characteristics of the contact component. <xr id="tab:Comparison of different coating processes"/><!--Table 7.7--> gives some indications for a comparative evaluation of the different coating processes.
The electroless metal coating is not covered here because of the low thickness of deposits which makes them in most cases not suitable for contact
applications.
<figtable id="tab:Comparison of different coating processes">
<caption>'''<!--Table 7.7:-->Comparison of different coating processes'''</caption>
{| 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
|> 1μm
|0.1 - approx. 10 μm <br />(in special cases up to 100 μm)
|0.1 approx. 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 foreign 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 main differences between the coating processes are found in the coating materials and thickness. While mechanical cladding and sputtering allow the use of almost any alloy material, electroplating processes are limited to metals and selected alloys such as for example high-carat gold alloys with up to .3 wt% Co or Ni. Electroplated and sputtered surface layers have a technological and economical upper thickness limit of about 10μm. While mechanical cladding has a minimum thickness of approx. 1 μm, electroplating and sputtering can also be easily applied in very thin layers down to the range of 0.1 μm.
The properties of the coatings are closely related to the coating process. Starting materials for cladding and sputtering targets precious metals and their alloys which in the case of gold and palladium based materials are vacuum melted and therefore exhibit a very high purity. During electroplating, depending on the type of electrolytes and the deposition parameters, some electrolyte components such as carbon and organic compounds are incorporated into the precious metal coating. Layers deposited from the gaseous phase however are very pure.
==<!--7.4-->Hot (-Dipped) Tin Coated Strip Materials==
During hot-dip tinning pre-treated strip materials are coated with pure tin or tin alloys from a liquid solder metal. During overall (or all-around) tinning the stripsthrough a liquid metal melt. For strip tinning rotating rolls are partially immersed into a liquid tin melt and transport the liquid onto the strip which is guided above them. Through special wiping and gas blowing procedures the deposited tin layer can be held within tight tolerances. Hot tinning is performed directly onto the base substrate material without any pre-coating with either copper or nickel. Special cast-on processes or the melting of solder foils onto the carrier strip allow also the production of thicker solder layers ( > 15 μm).
The main advantage of hot tinning of copper and copper alloys as compared to tin electroplating is the formation of an inter-metallic copper-tin phase (Cu<sub>3</sub>Sn, Cu<sub>6</sub>Sn<sub>5</sub>) at the boundary between the carrier material and the tin layer. This thin (0.3 – 0.5 μm) intermediate layer, which is formed during the thermal tinning process, is rather hard and reduces in connectors the frictional force and mechanical wear. Tin coatings produced by hot tinning have a good adhesion to the substrate material and do not tend to tin whisker formation.
A special process of hot tinning is the “Reflow” process. After depositing a tin coating by electroplating the layer is short-time melted in a continuous process.
The 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.
*'''Typical examples of hot tinned strip materials'''
[[File:Typical examples of hot tinned strip materials.jpg|left|Typical examples of hot tinned strip materials]]
<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 closely related to the standard for Cu and Cu alloy strips according to DIN EN 1652 and DIN 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 of sliding and connector contacts can be substantially reduced. In the electrical contact technology solid, as well as high and low viscosity liquid lubricants are used.
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 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
Solid lubricants include for example 0.05 – 0.2 μm thin hard gold layers which are added as surface layers on top of the actual contact material.
Among the various contact lubricants offered on the market contact lubrication oils have shown performance advantages. They are mostly synthetic, chemically inert, and silicone-free oils such as for example the DODUCONTA contact lubricants which differ in their chemical composition and viscosity.
For sliding contact systems with contact forces < 50 cN and higher sliding speeds oils with a lower viscosity (< 50 mPa·s) are preferential. For applications with higher contact forces and operating at higher temperatures contact oils with a higher viscosity are advantageous. Contact oils are mainly suited for applications at low current loads. At higher loads and in situations where contact separation occurs during the sliding operation thermal decomposition may be initiated which causes the lubricating properties to be lost.
Most compatible with plastics are the contact oil varieties B5, B12K, and B25, which also over longer operating times do not lead to tension stress corrosion.
For the optimum lubrication only a very thin layer of contact oil is required. Therefore it is for example recommended to dilute the oil in iso-propylenealcohol during the application to contact parts. After evaporation of the alcohol a thin and uniform layer of lubricant is retained on the contact surfaces.
*'''Properties of the Synthetic DODUCONTA Contact Lubricants'''
<table class="twocolortable">
<tr><th>Lubricant</th><th colspan="5">DODUCONTA</th></tr>
<th></th><th>B5</th><th>B9</th><th>B10</th><th>B12K</th><th>B25</th>
<tr><td><p class="s8">Contact force</p></td><td><p class="s8">>1N</p></td><td><p class="s8">0.1 - 2N</p></td><td><p class="s8">< 0.2N</p></td><td><p class="s8">0.2 - 5N</p></td><td><p class="s8"><1N</p></td></tr><tr><td><p class="s8">Density (20°C)</p><p class="s8">[g/cm³]</p></td><td><p class="s8">1.9</p></td><td><p class="s8">1.0</p></td><td><p class="s8">0.92</p></td><td><p class="s8">1.0</p></td><td><p class="s8">1.0</p></td></tr><tr><td><p class="s8">Specificel. Resis-</p><p class="s8">tance [<span class="s9">S · </span>cm]</p></td><td/><td><p class="s8">2 x 10<sup>10</sup></p></td><td><p class="s8">10<sup>10</sup></p></td><td><p class="s8">6 x 10<sup>9</sup></p></td><td><p class="s8">5 x 10<sup>8</sup></p></td></tr><tr><td><p class="s8">Viscosity (20°C)</p><p class="s8">[mPa·s]</p></td><td><p class="s8">325</p></td><td><p class="s8">47</p></td><td><p class="s8">21</p></td><td><p class="s8">235</p></td><td><p class="s8">405</p></td></tr><tr><td><p class="s8">Congeal temp.[°C]</p></td><td/><td><p class="s8">-55</p></td><td><p class="s8">-60</p></td><td><p class="s8">-40</p></td><td><p class="s8">-35</p></td></tr><tr><td><p class="s8">Flash point[°C]</p></td><td/><td><p class="s8">247</p></td><td><p class="s8">220</p></td><td><p class="s8">238</p></td><td><p class="s8">230</p></td></tr></table>
*'''Applications of the Synthetic DODUCONTA Contact Lubricants'''
<table class="twocolortable" style="text-align: left; font-size: 12px;width:80%">
<tr><th><p class="s8">Lubricant</p></th><th><p class="s8">Applications</p></th></tr>
<tr><td><p class="s8">DODUCONTA B5</p></td><td><p class="s8">Current collectors, connectors, slider switches</p></td></tr><tr><td><p class="s8">DODUCONTA B9</p></td><td><p class="s8">Wire potentiometers, slip rings, slider switches, measuring range selectors, miniature connectors</p></td></tr><tr><td><p class="s8">DODUCONTA B10</p></td><td><p class="s8">Precision wire potentiometers, miniature slip rings</p></td></tr><tr><td><p class="s8">DODUCONTA B12K</p></td><td><p class="s8">Wire potentiometers, slider switches, miniature slip rings, connectors</p></td></tr><tr><td><p class="s8">DODUCONTA B25</p></td><td><p class="s8">Current collectors, measuring range selectors, connectors</p></td></tr></table>
==<!--7.6-->Passivation of Silver Surfaces==
The formation of silver sulfide during the shelf life of components with silver surface in sulfur containing environments can be significantly eliminated by coating them with an additional protective film layer (Passivation layer). For electrical contact use such thin layers should be chemically inert and sufficiently conductive, or be 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|Typical process flow for the SILVERBRITE W ATPS process]]
</figure>
The passivation process SILVERBRITE W ATPS is a water-based tarnish preventer for silver. It is free of chromium(VI) compounds and solvents. The passivating layer is applied by immersion which creates a transparent organic protective film which barely changes the appearance and only slightly
increases the good electrical properties such as for example the contact resistance. The good solderability and bond properties of silver are not
negatively affected. Because of its chemical composition this protective layer has some lubricating properties which reduce the insertion and withdrawal forces of connectors noticeably.
<xr id="fig:Typical process flow for the SILVERBRITE W ATPS process"/> Typical process flow for the SILVERBRITE W ATPS process
==Referenzen==
Vinaricky, E. (Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
Springer-Verlag, Heidelberg 2002
Ganz, J.; Heber, J.; Macht, W.; Marka, E.: Galvanisch erzeugte
Edelmetallschichten für elektrische Kontakte. Metall 61 (2007) H.6, 394-398
Song, J.: Edelmetalle in Steckverbindungen - Funktionen und Einsparpotential.
VDE - Fachbericht 67 (2011) 13-22
Heber, J.: Galvanisch abgeschiedene Rhodiumschichten für den dekorativen
Bereich. Galvanotechnik, 98 (2007) H.12, 2931-2935
Johler, W.; Pöffel, K.; Weik, G.; Westphal, W.: High Temperature Resistance
th Galvanically Deposited Gold Layers for Switching Contacts. Proc. 15 Holm
Conf. on Electrical Contacts, Chicago (2005) 48-54
Grossmann, H. Schaudt, G.: Untersuchung über die Verwendbarkeit von
Überzügen der Platinmetallgruppe auf elektrotechnischen Verbindungselementen.
Galvanotechnik 67 (1976) 292-297
Grossmann, H.; Vinaricky, E.: Edelmetalleinsparung in der Elektrotechnik durch
selektives Galvanisieren. In: Handbuch der Galvanotechnik. München, Hanser-
Verlag, 37 (1981) 132-141
Grossmann, H.; Schaudt, G.: Hochgeschwindigkeitsabscheidung von Edelmetallen
auf Kontaktwerkstoffen. Galvanotechnik 84 (1993) H.5, 1541-1547
Bocking, C.; Cameron, B.: The Use of High Speed Selective Jet
Electrodeposition of Gold for the Plating of Connectors. Trans. IMF. 72 (1994)
33-40
Endres, B.: Selektive Beschichtungen von Kontaktmaterial im
Durchzugsverfahren. Metalloberfläche 39 (1985) H.11, 400-404
Kaspar, F.; Marka, E.; Normann, N.: Eigenschaften von chemisch Nickel
Goldschichten für Baugruppen der Elektrotechnik.
VDE Fachbericht 47 (1995) 19-27
Schmitt; W.; Kißling, S.; Behrens, V.: Elektrochemisch hergestellte
Schichtsysteme auf Aluminium für Kontaktanwendungen.
VDE - Fachbericht 67 (2011) 136-141
Freller, H.: Moderne PVD-Technologien zum Aufbringen dünner
Kontaktschichten. VDE-Fachbericht 40 (1989) 33-39
Ganz, J.: PVD-Verfahren als Ergänzung der Galvanik. Metalloberfläche 45 (1991)
Schmitt, W.; Franz, S.; Heber, J.; Lutz, O.; Behrens, V.: Formation of Silver
Sulfide Layers and their Influence on the Electrical Characteristics of Contacts in
th the Field of Information Technology. Proc. 24 Int. Conf.on Electr. Contacts,
Saint Malo, France (2008) 489-494
Buresch, I; Ganz, J.; Kaspar, F.: PVD-Beschichtungen und ihre Anwendungen
für Steckverbinder. VDE-Fachbericht 59 (2003) 73-80
Gehlert, B.: Edelmetalllegierungen für elektrische Kontakte.
Metall 61 (2007) H.6, 374-379
Ganz, J.: Einsatz von Sputterverfahren bei komplexen
Beschichtungsaufgaben. JOT 11 (1997)
Buresch, I.; Bögel, A.; Dürrschnabel, W.: Tin Coating for Electrical Components.
Metall 48 (1994) H.1, 11-14
Buresch, I.; Horn, J.: Bleifreie Zinnoberflächen.
VDE-Fachbericht 61 (2005) 89-94
Adler, U.; Buresch, I.; Riepe, U.; Tietz, V.: Charakteristische Eigenschaften der
schmelzflüssigen Verzinnung von Kupferwerkstoffen.
VDE-Fachbericht 63 (2007) 175-180
Huck, M.: Einsatz von Schmiermitteln auf Gleit- und Steckkontakten.
Metalloberfläche (1982) 429-435
Abbott, W.,H.: Field and Laboratory Studies of Corrosion Inhibiting Lubricants
for Gold-Plated Connectors. Proc. HOLM Conf.on Electrical Contacts, Chicago
(1996) 414-428
Noel, S.; Alarmaguy, D.; Correia, S.; Gendre, P.: Study of Thin Underlayers to
Hinder Contact resistance Increase Due to Intermetallic Compound Formation.
th Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, BC,
Canada (2009) 153 – 159
Weik, G.; Johler, W.; Schrank, C.: Zuverlässigkeit und Eigenschaften von Gold –
Schichten bei hohen Einsatztemperaturen.
VDE – Fachbericht 65, (2009) 13 – 21
Buresch, I.; Hack, M.: Eigenschaften von Zinnschichten für elektromechanische
Bauelemente – Einflussfaktoren und ihre Auswirkungen. VDE – Fachbericht 65,
(2009) 23 – 30
Buresch, I.: Effekte intermetallischer Phasen auf die Eigenschaften von
Zinnoberflächen auf Kupferlegierungen. VDE – Fachbericht 67 (2011) 38-46
Schmitt, W.; Heber, J.; Lutz, O.; Behrens, V.: Einfluss des Herstellverfahrens auf
das Korrosions- und Kontaktverhalten von Ag – Beschichtungen in
schwefelhaltiger Umgebung. VDE – Fachbericht 65 (2009) 51 – 58
[[en:Surface_Coating_Technologies]]
schmelz- oder pulvermetallurgischem Wege, bietet sich die Herstellung über die
flüssige und gasförmige Phase vor allem dann an, wenn dünne Schichten im
μm-Bereich benötigt werden, die nach den üblichen Plattiertechniken nicht
wirtschaftlich herstellbar sind <xr id="tab:Overview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications"/><!--(Tab. 7.1)-->. Derartige Schichten erfüllen, abhängig
von ihrer chemischen Zusammensetzung und Dicke, unterschiedliche
Anforderungen. Sie dienen z.B. als Korrosions- und Verschleißschutz oder
übernehmen die Funktion einer Kontaktschicht, an die bestimmte technische
Anforderungen gestellt werden. Daneben stellen sie für dekorative Zwecke eine
optisch ansprechende und verschleißfeste Oberflächenschicht dar.
<figtable id="tab:Overview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications">
<caption>'''<!--Table 7.1:-->Übersicht über einige wichtige Eigenschaften galvanisch abgeschiedener Schichten und die jeweiligen Anwendungen'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
|-
!Eigenschaften
!Anwendungszweck
!Anwendungsbeispiele
|-
|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">*) Koerzitivkraft = Kraft, mit der ein Stoff versucht, die einmal angenommene Magnetisierung zu behalten</div>
Um den mechanischen Verschleiß bei dünnen Schichten zu verringern,
kommen bei Gleit- und Steckkontakten Schmiermittel meist in flüssiger Form
zum Einsatz. Bei Silber-Kontakten bieten sog. Passivierungsschichten einen
Schutz gegenüber Silbersulfidbildung.
==Beschichtung über die flüssige Phase==
Für dünne, über die flüssige Phase erzeugte Schichten bieten sich zwei Herstellungsverfahren
an. Sie unterscheiden sich dadurch, dass die metallische
Abscheidung mit oder ohne äußere Stromquelle erfolgt. Im ersten Fall handelt
es sich um eine galvanische Beschichtung, im zweiten um eine chemische
Beschichtung.
===Galvanische Beschichtung===
Zur galvanischen Abscheidung von Metallen, insbesondere Edelmetallen,
werden wässrige Lösungen (Elektrolyte) verwendet, die die abzuscheidenden
Metalle in Form von Ionen (z.B. gelöste Metallsalze) enthalten. Unter dem
Einfluss eines elektrischen Feldes zwischen der Anode und dem kathodisch
geschalteten Beschichtungsgut gelangen positiv geladene Metallionen zur
Kathode, wo sie ihre Ladung abgeben und sich als Metall auf der Oberfläche
abscheiden.
Je nach Einsatz, in der Elektrotechnik und Elektronik oder für dekorative
Zwecke, kommen unterschiedliche galvanische Bäder (Elektrolyte) zur
Anwendung. Die für die Edelmetallbeschichtung eingesetzten Galvanisieranlagen
und der Umfang ihrer Ausrüstung werden durch den vorgesehenen
technologischen Prozess bestimmt.
Die galvanischen Arbeitsverfahren erstrecken sich nicht nur auf den Vorgang
der reinen elektrochemischen Metallabscheidung, sondern umfassen auch die
Vor- und Nachbehandlung der zu beschichtenden Ware. Wichtigste Voraussetzung
für die Herstellung eines festhaftenden Überzuges ist eine metallisch
blanke, d.h. fett- und oxidfreie Oberfläche des zu veredelnden Werkstückes.
Hierfür gibt es verschiedene Vorbehandlungsverfahren, die auf den Oberflächenzustand
und die Eigenschaften des Werkstoffes abgestimmt sind.
In den folgenden Abschnitten werden galvanische Bäder - Edelmetall- und
Unedelmetallbäder - sowie die wichtigsten Galvanisierverfahren beschrieben.
siehe Artikel: [[Galvanische_Beschichtung| Galvanische Beschichtung]]
===<!--7.1.2-->Stromlose Beschichtung===
Unter stromloser Metallabscheidung versteht man Beschichtungsverfahren, die
ohne Anwendung einer äußeren Stromquelle ablaufen. Sie ermöglichen eine
gleichmäßige Metallbeschichtung unabhängig von der geometrischen Form der
zu beschichtenden Teile. Aufgrund der sehr guten Streufähigkeit dieser Bäder
lassen sich z.B. auch Innenseiten von Bohrungen beschichten.
Prinzipiell können zwei Verfahren der außenstromlosen Metallabscheidung
unterschieden werden: Verfahren, bei denen das zu beschichtende Substratmaterial
als Reduktionsmittel dient (Austauschverfahren), und solche, bei denen
dem Elektrolyt ein Reduktionsmittel zugesetzt wird (Reduktionsverfahren).
siehe Artikel: [[Stromlose_Beschichtung| Stromlose Beschichtung]]
==<!--7.2-->Beschichtung über die Gasphase (Vakuumbeschichtung)==
Unter der Bezeichnung PVD (physical vapor deposition) werden Beschichtungsverfahren
zusammengefasst, bei denen die Abscheidung von Metallen, Legierungen
sowie chemischen Verbindungen im Vakuum durch Zufuhr thermischer
oder kinetischer Energie mittels Teilchenbeschuss erfolgt. Dabei unterscheidet
man hauptsächlich vier Beschichtungsvarianten <xr id="tab:Characteristics of the Most Important PVD Processes"/><!--(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 the substrate and deposited on it as a thin layer (a few nm to approx. 10 μm)
<figtable id="tab:Characteristics of the Most Important PVD Processes">
<caption>'''<!--Table 7.6:-->Characteristics of the Most Important PVD Processes'''</caption>
{| 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<sup>-3</sup> Pa
|< 2eV
|Separation of alloy components may occur
|-
|Arc vaporizing
|Vaporizing of the 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 the target plate<br />(cathode) 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>
The sputtering process has gained the economically most significant usage. Its process principle is illustrated in <xr id="fig:Principle of sputtering"/><!--(Fig. 7.5)-->.
<figure id="fig:Principle of sputtering">
[[File:Principle of sputtering.jpg|right|thumb|Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms]]
</figure>
Initially a gas discharge is ignited in a low pressure (10<sup>-1</sup> -1 Pa) argon atmosphere. The argon ions generated are accelerated in an electric field and impact the target of material to be deposited with high energy. Caused by this energy atoms are released from the target material which condensate on the oppositely arranged anode (the substrate) and form a layer with high adhesion strength. Through an overlapping magnetic field at the target location the deposition rate can be increased, making the process more economical.
The advantages of the PVD processes and especially sputtering for electrical contact applications are:
*High purity of the deposit layers
*Low thermal impact on the substrate
*Almost unlimited coating materials
*Low coating thickness tolerance
*Excellent adhesion (also by using additional intermediate layers)
Coatings produced by PVD processes are used for contact applications, for example on miniature-profiles, in electrical engineering and for electronic components, for solderability in joining processes, for metalizing of nonconductive materials, as well as in semiconductors, opto-electronics, optics, and medical technology applications.
There are few limitations regarding the geometrical shape of substrate parts. Only the interior coating of drilled holes and small diameter tubing can be more problematic (ratio of depth to diameter should be < 2:1). Profile wires, strips, and foils can be coated from one side or both; formed parts can be coated selectively by using masking fixtures that at the same time serve as holding fixtures.
*'''Examples of vacuum coated semi-finished materials and parts'''
[[File:Examples of vacuum coated semi finished materials and parts.jpg|left|Examples of vacuum coated semi finished materials and parts]]
<br style="clear:both;"/>
*'''Materials'''
Selection of possible combinations of coating and substrate materials
<table class="twocolortable">
<tr><th rowspan="2"><p class="s8">Substrate Materials</p></th><th colspan="12"><p class="s8">Coating Materials</p></th></tr>
<tr><th><p><span>Ag</span></p></th><th><p><span>Au</span></p></th><th><p><span>Pt</span></p></th><th><p><span>Pd</span></p></th><th><p><span>Cu</span></p></th><th><p><span>Ni</span></p></th><th><p><span>Ti</span></p></th><th><p><span>Cr</span></p></th><th><p><span>Mo</span></p></th><th><p><span>W</span></p></th><th><p><span>Ai</span></p></th><th><p><span>Si</span></p></th></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>[[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>
[[File:K7-gef.png]] can be produced
[[File:K7-leer.png]] can be produced with intermediate layer
*'''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 few restrictions. 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, internal standards, and customer specifications resp.
==<!--7.3-->Comparison of Deposition Processes==
The individual deposition processes have in part different performance characteristics. For each end application the optimal process has to be chosen considering all technical and economical factors. The main selection criteria should be based on the electrical and mechanical requirements for the contact layer and on the design characteristics of the contact component. <xr id="tab:Comparison of different coating processes"/><!--Table 7.7--> gives some indications for a comparative evaluation of the different coating processes.
The electroless metal coating is not covered here because of the low thickness of deposits which makes them in most cases not suitable for contact
applications.
<figtable id="tab:Comparison of different coating processes">
<caption>'''<!--Table 7.7:-->Comparison of different coating processes'''</caption>
{| 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
|> 1μm
|0.1 - approx. 10 μm <br />(in special cases up to 100 μm)
|0.1 approx. 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 foreign 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 main differences between the coating processes are found in the coating materials and thickness. While mechanical cladding and sputtering allow the use of almost any alloy material, electroplating processes are limited to metals and selected alloys such as for example high-carat gold alloys with up to .3 wt% Co or Ni. Electroplated and sputtered surface layers have a technological and economical upper thickness limit of about 10μm. While mechanical cladding has a minimum thickness of approx. 1 μm, electroplating and sputtering can also be easily applied in very thin layers down to the range of 0.1 μm.
The properties of the coatings are closely related to the coating process. Starting materials for cladding and sputtering targets precious metals and their alloys which in the case of gold and palladium based materials are vacuum melted and therefore exhibit a very high purity. During electroplating, depending on the type of electrolytes and the deposition parameters, some electrolyte components such as carbon and organic compounds are incorporated into the precious metal coating. Layers deposited from the gaseous phase however are very pure.
==<!--7.4-->Hot (-Dipped) Tin Coated Strip Materials==
During hot-dip tinning pre-treated strip materials are coated with pure tin or tin alloys from a liquid solder metal. During overall (or all-around) tinning the stripsthrough a liquid metal melt. For strip tinning rotating rolls are partially immersed into a liquid tin melt and transport the liquid onto the strip which is guided above them. Through special wiping and gas blowing procedures the deposited tin layer can be held within tight tolerances. Hot tinning is performed directly onto the base substrate material without any pre-coating with either copper or nickel. Special cast-on processes or the melting of solder foils onto the carrier strip allow also the production of thicker solder layers ( > 15 μm).
The main advantage of hot tinning of copper and copper alloys as compared to tin electroplating is the formation of an inter-metallic copper-tin phase (Cu<sub>3</sub>Sn, Cu<sub>6</sub>Sn<sub>5</sub>) at the boundary between the carrier material and the tin layer. This thin (0.3 – 0.5 μm) intermediate layer, which is formed during the thermal tinning process, is rather hard and reduces in connectors the frictional force and mechanical wear. Tin coatings produced by hot tinning have a good adhesion to the substrate material and do not tend to tin whisker formation.
A special process of hot tinning is the “Reflow” process. After depositing a tin coating by electroplating the layer is short-time melted in a continuous process.
The 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.
*'''Typical examples of hot tinned strip materials'''
[[File:Typical examples of hot tinned strip materials.jpg|left|Typical examples of hot tinned strip materials]]
<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 closely related to the standard for Cu and Cu alloy strips according to DIN EN 1652 and DIN 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 of sliding and connector contacts can be substantially reduced. In the electrical contact technology solid, as well as high and low viscosity liquid lubricants are used.
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 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
Solid lubricants include for example 0.05 – 0.2 μm thin hard gold layers which are added as surface layers on top of the actual contact material.
Among the various contact lubricants offered on the market contact lubrication oils have shown performance advantages. They are mostly synthetic, chemically inert, and silicone-free oils such as for example the DODUCONTA contact lubricants which differ in their chemical composition and viscosity.
For sliding contact systems with contact forces < 50 cN and higher sliding speeds oils with a lower viscosity (< 50 mPa·s) are preferential. For applications with higher contact forces and operating at higher temperatures contact oils with a higher viscosity are advantageous. Contact oils are mainly suited for applications at low current loads. At higher loads and in situations where contact separation occurs during the sliding operation thermal decomposition may be initiated which causes the lubricating properties to be lost.
Most compatible with plastics are the contact oil varieties B5, B12K, and B25, which also over longer operating times do not lead to tension stress corrosion.
For the optimum lubrication only a very thin layer of contact oil is required. Therefore it is for example recommended to dilute the oil in iso-propylenealcohol during the application to contact parts. After evaporation of the alcohol a thin and uniform layer of lubricant is retained on the contact surfaces.
*'''Properties of the Synthetic DODUCONTA Contact Lubricants'''
<table class="twocolortable">
<tr><th>Lubricant</th><th colspan="5">DODUCONTA</th></tr>
<th></th><th>B5</th><th>B9</th><th>B10</th><th>B12K</th><th>B25</th>
<tr><td><p class="s8">Contact force</p></td><td><p class="s8">>1N</p></td><td><p class="s8">0.1 - 2N</p></td><td><p class="s8">< 0.2N</p></td><td><p class="s8">0.2 - 5N</p></td><td><p class="s8"><1N</p></td></tr><tr><td><p class="s8">Density (20°C)</p><p class="s8">[g/cm³]</p></td><td><p class="s8">1.9</p></td><td><p class="s8">1.0</p></td><td><p class="s8">0.92</p></td><td><p class="s8">1.0</p></td><td><p class="s8">1.0</p></td></tr><tr><td><p class="s8">Specificel. Resis-</p><p class="s8">tance [<span class="s9">S · </span>cm]</p></td><td/><td><p class="s8">2 x 10<sup>10</sup></p></td><td><p class="s8">10<sup>10</sup></p></td><td><p class="s8">6 x 10<sup>9</sup></p></td><td><p class="s8">5 x 10<sup>8</sup></p></td></tr><tr><td><p class="s8">Viscosity (20°C)</p><p class="s8">[mPa·s]</p></td><td><p class="s8">325</p></td><td><p class="s8">47</p></td><td><p class="s8">21</p></td><td><p class="s8">235</p></td><td><p class="s8">405</p></td></tr><tr><td><p class="s8">Congeal temp.[°C]</p></td><td/><td><p class="s8">-55</p></td><td><p class="s8">-60</p></td><td><p class="s8">-40</p></td><td><p class="s8">-35</p></td></tr><tr><td><p class="s8">Flash point[°C]</p></td><td/><td><p class="s8">247</p></td><td><p class="s8">220</p></td><td><p class="s8">238</p></td><td><p class="s8">230</p></td></tr></table>
*'''Applications of the Synthetic DODUCONTA Contact Lubricants'''
<table class="twocolortable" style="text-align: left; font-size: 12px;width:80%">
<tr><th><p class="s8">Lubricant</p></th><th><p class="s8">Applications</p></th></tr>
<tr><td><p class="s8">DODUCONTA B5</p></td><td><p class="s8">Current collectors, connectors, slider switches</p></td></tr><tr><td><p class="s8">DODUCONTA B9</p></td><td><p class="s8">Wire potentiometers, slip rings, slider switches, measuring range selectors, miniature connectors</p></td></tr><tr><td><p class="s8">DODUCONTA B10</p></td><td><p class="s8">Precision wire potentiometers, miniature slip rings</p></td></tr><tr><td><p class="s8">DODUCONTA B12K</p></td><td><p class="s8">Wire potentiometers, slider switches, miniature slip rings, connectors</p></td></tr><tr><td><p class="s8">DODUCONTA B25</p></td><td><p class="s8">Current collectors, measuring range selectors, connectors</p></td></tr></table>
==<!--7.6-->Passivation of Silver Surfaces==
The formation of silver sulfide during the shelf life of components with silver surface in sulfur containing environments can be significantly eliminated by coating them with an additional protective film layer (Passivation layer). For electrical contact use such thin layers should be chemically inert and sufficiently conductive, or be 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|Typical process flow for the SILVERBRITE W ATPS process]]
</figure>
The passivation process SILVERBRITE W ATPS is a water-based tarnish preventer for silver. It is free of chromium(VI) compounds and solvents. The passivating layer is applied by immersion which creates a transparent organic protective film which barely changes the appearance and only slightly
increases the good electrical properties such as for example the contact resistance. The good solderability and bond properties of silver are not
negatively affected. Because of its chemical composition this protective layer has some lubricating properties which reduce the insertion and withdrawal forces of connectors noticeably.
<xr id="fig:Typical process flow for the SILVERBRITE W ATPS process"/> Typical process flow for the SILVERBRITE W ATPS process
==Referenzen==
Vinaricky, E. (Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
Springer-Verlag, Heidelberg 2002
Ganz, J.; Heber, J.; Macht, W.; Marka, E.: Galvanisch erzeugte
Edelmetallschichten für elektrische Kontakte. Metall 61 (2007) H.6, 394-398
Song, J.: Edelmetalle in Steckverbindungen - Funktionen und Einsparpotential.
VDE - Fachbericht 67 (2011) 13-22
Heber, J.: Galvanisch abgeschiedene Rhodiumschichten für den dekorativen
Bereich. Galvanotechnik, 98 (2007) H.12, 2931-2935
Johler, W.; Pöffel, K.; Weik, G.; Westphal, W.: High Temperature Resistance
th Galvanically Deposited Gold Layers for Switching Contacts. Proc. 15 Holm
Conf. on Electrical Contacts, Chicago (2005) 48-54
Grossmann, H. Schaudt, G.: Untersuchung über die Verwendbarkeit von
Überzügen der Platinmetallgruppe auf elektrotechnischen Verbindungselementen.
Galvanotechnik 67 (1976) 292-297
Grossmann, H.; Vinaricky, E.: Edelmetalleinsparung in der Elektrotechnik durch
selektives Galvanisieren. In: Handbuch der Galvanotechnik. München, Hanser-
Verlag, 37 (1981) 132-141
Grossmann, H.; Schaudt, G.: Hochgeschwindigkeitsabscheidung von Edelmetallen
auf Kontaktwerkstoffen. Galvanotechnik 84 (1993) H.5, 1541-1547
Bocking, C.; Cameron, B.: The Use of High Speed Selective Jet
Electrodeposition of Gold for the Plating of Connectors. Trans. IMF. 72 (1994)
33-40
Endres, B.: Selektive Beschichtungen von Kontaktmaterial im
Durchzugsverfahren. Metalloberfläche 39 (1985) H.11, 400-404
Kaspar, F.; Marka, E.; Normann, N.: Eigenschaften von chemisch Nickel
Goldschichten für Baugruppen der Elektrotechnik.
VDE Fachbericht 47 (1995) 19-27
Schmitt; W.; Kißling, S.; Behrens, V.: Elektrochemisch hergestellte
Schichtsysteme auf Aluminium für Kontaktanwendungen.
VDE - Fachbericht 67 (2011) 136-141
Freller, H.: Moderne PVD-Technologien zum Aufbringen dünner
Kontaktschichten. VDE-Fachbericht 40 (1989) 33-39
Ganz, J.: PVD-Verfahren als Ergänzung der Galvanik. Metalloberfläche 45 (1991)
Schmitt, W.; Franz, S.; Heber, J.; Lutz, O.; Behrens, V.: Formation of Silver
Sulfide Layers and their Influence on the Electrical Characteristics of Contacts in
th the Field of Information Technology. Proc. 24 Int. Conf.on Electr. Contacts,
Saint Malo, France (2008) 489-494
Buresch, I; Ganz, J.; Kaspar, F.: PVD-Beschichtungen und ihre Anwendungen
für Steckverbinder. VDE-Fachbericht 59 (2003) 73-80
Gehlert, B.: Edelmetalllegierungen für elektrische Kontakte.
Metall 61 (2007) H.6, 374-379
Ganz, J.: Einsatz von Sputterverfahren bei komplexen
Beschichtungsaufgaben. JOT 11 (1997)
Buresch, I.; Bögel, A.; Dürrschnabel, W.: Tin Coating for Electrical Components.
Metall 48 (1994) H.1, 11-14
Buresch, I.; Horn, J.: Bleifreie Zinnoberflächen.
VDE-Fachbericht 61 (2005) 89-94
Adler, U.; Buresch, I.; Riepe, U.; Tietz, V.: Charakteristische Eigenschaften der
schmelzflüssigen Verzinnung von Kupferwerkstoffen.
VDE-Fachbericht 63 (2007) 175-180
Huck, M.: Einsatz von Schmiermitteln auf Gleit- und Steckkontakten.
Metalloberfläche (1982) 429-435
Abbott, W.,H.: Field and Laboratory Studies of Corrosion Inhibiting Lubricants
for Gold-Plated Connectors. Proc. HOLM Conf.on Electrical Contacts, Chicago
(1996) 414-428
Noel, S.; Alarmaguy, D.; Correia, S.; Gendre, P.: Study of Thin Underlayers to
Hinder Contact resistance Increase Due to Intermetallic Compound Formation.
th Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, BC,
Canada (2009) 153 – 159
Weik, G.; Johler, W.; Schrank, C.: Zuverlässigkeit und Eigenschaften von Gold –
Schichten bei hohen Einsatztemperaturen.
VDE – Fachbericht 65, (2009) 13 – 21
Buresch, I.; Hack, M.: Eigenschaften von Zinnschichten für elektromechanische
Bauelemente – Einflussfaktoren und ihre Auswirkungen. VDE – Fachbericht 65,
(2009) 23 – 30
Buresch, I.: Effekte intermetallischer Phasen auf die Eigenschaften von
Zinnoberflächen auf Kupferlegierungen. VDE – Fachbericht 67 (2011) 38-46
Schmitt, W.; Heber, J.; Lutz, O.; Behrens, V.: Einfluss des Herstellverfahrens auf
das Korrosions- und Kontaktverhalten von Ag – Beschichtungen in
schwefelhaltiger Umgebung. VDE – Fachbericht 65 (2009) 51 – 58
[[en:Surface_Coating_Technologies]]
