Difference between revisions of "Surface Coating Technologies"

From Electrical Contacts
Jump to: navigation, search
 
(132 intermediate revisions by 6 users not shown)
Line 1: Line 1:
Besides manufacturing contact materials from the solid phase, i.e. by melt or
+
Besides manufacturing contact materials from the solid phase, i.e. by melt or powder metallurgy, the production starting in the liquid or gaseous phase is generally preferred when thin layers within the μm range are required, which cannot be obtained economically by conventional cladding methods (<xr id="tab:Overview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications"/><!--(Tab. 7.1)-->). Such coatings fulfill different requirements depending on their composition and thickness.
powder metallurgy, the production starting in the liquid or gaseous phase is
+
They can serve as corrosion or wear protection or can fulfill the need for thin contact layers for certain technical applications. In addition they serve for decorative purposes as a pleasing and wear resistant surface coating.
generally preferred when thin layers in the μm range are required which cannot
 
be obtained economically by conventional cladding methods. Such coatings
 
fulfill different requirements depending on their composition and thickness.
 
They can serve as corrosion or wear protection or can fulfill the need for thin
 
contact layers for certain technical applications. In addition they serve for
 
decorative purposes as a pleasing and wear resistant surface coating.
 
  
Table 7.1: Overview of Important Properties of Electroplated Coatings
+
<figtable id="tab:Overview_of_Important_Properties_of_Electroplated_Coatings_and_their_Applications">
and their Applications
+
<caption>'''<!--Table 7.1:-->Overview of Important Properties of Electroplated Coatings and their Applications'''</caption>
  
To reduce the mechanical wear of thin surface layers on sliding and connector
+
{| class="twocolortable" style="text-align: left; font-size: 12px"
contacts additional lubricants in liquid form are often used. On silver contacts
+
|-
passivation coatings are applied as protection against silver sulfide formation.
+
!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>
  
===7.1 Coatings from the Liquid Phase===
+
To reduce the mechanical wear of thin surface layers on sliding and connector contacts, additional lubricants in liquid form are often used. On silver contacts, passivation coatings are applied as protection against silver sulfide formation.
For thin coatings starting from the liquid phase two processes are used
 
differentiated by the metallic deposition being performed either with or without
 
the use of an external electrical current source. The first one is electroplating
 
while the second one is a chemical deposition process.
 
  
===7.1.1 Electroplating (or Galvanic Deposition)===
+
==Coatings from the Liquid Phase==
For electroplating of metals, especially precious metals, water based solutions
+
For thin coatings starting from the liquid phase, two processes are used differentiated by the metallic deposition being performed either with or without the use of an external electrical current source. The first one is electroplating, while the second one is a chemical deposition process.
(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 pieces
 
as the cathode forces the positively charged metal ions to move to the cathode
 
where they give up their charge and deposit themselves as metal on the surface
 
of the work piece.
 
Depending on the application, for electric and electronic or decorative end use,
 
different electrolytic bath solutions (electrolytes) are used. The electroplating
 
equipment 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 important
 
parameter for creating strongly adhering deposits is the surface of the goods to
 
be metallic clean without oily or oxide film residues. This is achieved through
 
various pre-treatment processes specifically developed for the types of material
 
and surface conditions of the goods to be plated.
 
In the following segments electrolytes – both precious and non-precious – as
 
well as the most widely used electroplating processes are described.
 
  
===7.1.1.1 Electroplating Solutions – Electrolytes===
+
=== Electroplating (or Galvanic Deposition)===
The actual metal deposition occurs in the electrolytic solution which contains
+
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 pieces as the cathode, forces the positively charged metal ions to move to the cathode where they give up their charge and deposit themselves as metal on the surface of the work piece.
the plating material as metal ions. Besides this basic ingredient, the electrolytes
+
Depending on the application, for electric and electronic or decorative end use, different electrolytic bath solutions (electrolytes) are used. The electroplating equipment used for precious metal plating and its complexity varies widely, depending on the process technologies employed.
contain additional components depending on the processes used, such as for
+
Electroplating processes are encompassing, besides the pure metal deposition, also preparative and post treatments of the goods to be coated. An important parameter for creating strongly adhering deposits is that the surface of the goods has to be metallic clean without oily or oxide film residues. This is achieved through various pre-treatment processes, specifically developed for the types of material and surface conditions of the goods to be plated.
example conduction salts, brighteners, and organic additives which are codeposited
+
In the following segments, electrolytes – both precious and non-precious – as well as the most widely used electroplating processes are described.
into the coatings, influencing the final properties of the electroplating
 
deposit.
 
  
===7.1.1.1.1 Precious Metal Electrolytes===
+
Main Articel: [[Electroplating (or Galvanic Deposition)| Electroplating (or Galvanic Deposition)]]
All precious metals can be electroplated with silver and gold by far the most
 
widely used ones ''(Tables 7.1 and 7.2)''.
 
The following precious metal electrolytes are the most important ones:
 
  
*'''Gold electrolytes''' For functional and decorative purposes pure gold, hard gold, low-karat gold, or colored gold coatings are deposited. Depending on the requirements, acidic, neutral, or cyanide electrolytes based on potassium gold cyanide or cyanide free and neutral electrolytes based on gold sulfite complexes are used.
+
===<!--7.1.2-->Electroless Plating===
  
*'''Palladium and Platinum electrolytes''' Palladium is mostly deposited as a pure metal, for applications in electrical contacts however also as palladium nickel. For higher value jewelry allergy protective palladium intermediate layers are used as a diffusion barrier over copper alloy substrate materials. Platinum is mostly used as a surface layer on jewelry items.
+
Electroless plating is defined as a coating process which is performed without the use of an external current source. It allows a uniform metal coating, independent of the geometrical shape of the parts, to be coated. Because of the very good dispersion capability of the used electrolytes, also cavities and the inside of drilled holes in parts can be coated for example.
 +
In principal, two different mechanisms are employed for electroless plating: processes in which the carrier material serves as a reduction agent (Immersion processes) and those in which a reduction agent is added to the electrolyte (Electroless processes).
  
*'''Ruthenium electrolytes''' Ruthenium coatings are mostly used for decorative purposes creating a fashionable “grey” ruthenium color on the surface. An additional color variation is created by using “ruthenium-black” deposits which are mainly used in bi-color decorative articles.
+
Main Articel: [[Electroless Plating| Electroless Plating]]
  
*'''Rhodium electrolytes''' Rhodium deposits are extremely hard (HV 700 – 1000) 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.
+
==<!--7.2-->Coatings from the Gaseous Phase (Vacuum Deposition)==
 +
The term PVD (physical vapor deposition) defines processes of metal, metal alloys and chemical compounds deposition in a vacuum by adding thermal and kinetic energy by particle bombardment. The main processes are the following four coating variations (<xr id="tab:Characteristics of the Most Important PVD Processes"/><!--(Table 7.6-->):
  
*'''Silver electrolytes''' Silver electrolytes without additives generate dull soft deposits (HV ~ 80) which are mainly used as contact layers on connectors with limited insertion and withdrawal cycles. Properties required for decorative purposes such as shiny bright surfaces and higher wear resistance are achieved through various additives to the basic Ag electrolyte.
+
*Vapor deposition   
 +
*Sputtering (Cathode atomization)
 +
*Arc vaporizing     
 +
*Ion implantation
  
Table 7.2: Precious Metal Electrolytes for Technical Applications
+
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)
  
===7.1.1.1.2 Non-Precious Metal Electrolytes===
 
The most important non-precious metals that are deposited by electroplating
 
are: Copper, nickel, tin, and zinc and their alloys. The deposition is performed in
 
the form of pure metals with different electrolytes used ''(Table 7.4).''
 
  
*'''Copper electrolytes''' Copper electrolytes are used for either depositing an intermediate layer on strips or parts, for building up a printed circuit board structure, or for the final strengthening during the production of printed circuit boards.
+
<figtable id="tab:Characteristics of the Most Important PVD Processes">
 +
<caption>'''<!--Table 7.6:-->Characteristics of the Most Important PVD Processes'''</caption>
  
*'''Tin electrolytes''' Pure tin and tin alloy deposits are used as dull or also bright surface layers on surfaces required for soldering. In the printed circuit board manufacturing they are also utilized as an etch resist for the conductive pattern design after initial copper electroplating.
+
{| 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>
  
Table 7.3: Precious Metal Electrolytes for Decorative Applications
 
  
*'''Nickel electrolytes''' Nickel layers are mostly used as diffusion barriers during the gold plating of copper and copper alloys or as an intermediate layer for tinning
+
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)-->).
  
*'''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 the bronze layers are utilized for their good corrosion resistance and good brazing and soldering properties.
+
<figure id="fig:Principle of sputtering">
 +
[[File:Principle of sputtering.jpg|right|thumb|Figure 1: Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms]]
 +
</figure>
 +
Initially, a gas discharge is ignited in 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.
  
Table 7.2: Typical Electrolytes for the Deposition of Non-Precious Metals
+
The advantages of the PVD processes and especially sputtering for electrical contact applications are:
  
===7.1.1.2 Electroplating of Parts===
+
*High purity of the deposit layers 
The complete or all-around electroplating of small mass produced parts like
+
*Low thermal impact on the substrate
contact springs, rivets, or pins is usually done as mass plating in electroplating
+
*Almost unlimited coating materials 
barrels of different shape. During the electroplating process the parts are
+
*Low coating thickness tolerance   
continuously moved and mixed to reach a uniform coating.
+
*Excellent adhesion (also by using additional intermediate layers)
  
Larger parts are frequently electroplated on racks either totally or by different
+
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.
masking techniques also partially. Penetrating the coating into the interior of
 
drilled holes or tubes can be achieved with the use of special fixtures.
 
  
===Electroplated Parts===
+
There are few limitations regarding the geometrical shape of substrate parts. Only the interior coating of drilled holes and small diameter tubing can be more problematic (ratio of depth to diameter should be < 2:1). Profile wires, strips and foils can be coated from one side or both; formed parts can be coated selectively by using masking fixtures that at the same time serve as holding fixtures  (<xr id="fig:Examples of vacuum coated semi finished materials and parts"/>).
bild
 
  
 +
<figure id="fig:Examples of vacuum coated semi finished materials and parts">
 +
[[File:Examples of vacuum coated semi finished materials and parts.jpg|left|Figure 2: Examples of vacuum coated semi finished materials and parts]]
 +
</figure>
 +
 +
<br style="clear:both;"/>
 
*'''Materials'''
 
*'''Materials'''
 +
Selection of possible combinations of coating and substrate materials
  
*'''Coating thickness'''
+
<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>
  
Precious metals: 0.2 – 5 μm (typical layer thicknesses; for Ag also up to 25 μm)
+
[[File:K7-gef.png]] can be produced
Non-precious metals: Up to approx. 20 μm
+
[[File:K7-leer.png]] can be produced with intermediate layer
Tolerances: Strongly varying depending on the geometrical shape of
 
parts (up to 50% at a defined measuring spot).
 
It is recommended to specify a minimum value for the
 
coating thickness at a defined measuring spot
 
  
als Bild?
+
*'''Dimensions'''
  
*'''Quality criteria'''  
+
{| class="twocolortable" style="text-align: left; font-size: 12px;width:40%"
Besides others the following layer parameters are typically monitored in-process and documented:
+
|-
 +
!colspan="2" style="text-align:center"|'''Dimensions'''
 +
|-
 +
|Coating thickness:
 +
|10 nm - 15 μm
 +
|-
 +
|Coating thicknesses for contact applications:
 +
|0.1 - 10 μm
 +
|}
  
*Coating thickness  *Solderability
+
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
*Adhesion strength  *Bonding property
+
limitations.
*Porosity Contact  *resistance
 
  
These quality tests are performed according to industry standards, internal
+
*'''Tolerances'''
standards, and customer specifications resp.
 
  
===7.1.1.3 Electroplating of Semi-finished Materials===
+
Coating thickness &#177;10 - 30 %, depending on the thickness
The process for overall electroplating of strips, profiles, and wires is mostly
 
performed on continuously operating reel-to-reel equipment. The processing
 
steps for the individual operations such as pre-cleaning, electroplating, rinsing
 
are following the same principles as those employed in parts electroplating.
 
  
The overall coating is usually applied for silver plating and tin coating of strips
+
*'''Quality criteria'''
and wires. Compared to hard gold or palladium these deposits are rather
+
Depending on the application, the following parameters are tested and recorded (see also: Electroplating of parts):
ductile, ensuring that during following stamping and forming operations no
 
cracks are generated in the electroplated layers.
 
  
===7.1.1.4 Selective Electroplating===
+
*Coating thickness 
Since precious metals are rather expensive it is necessary to perform the
+
*Solderability
electroplating most economically and coat only those areas that need the layers
+
*Adhesion strength 
for functional purposes. This leads from overall plating to selective
+
*Bonding property
electroplating of strip material in continuous reel-to-reel processes. Depending
+
*Porosity         
on the final parts design and the end application the processes can be applied
+
*Contact resistance
to solid strip material as well as pre-stamped and formed continuous strips or
 
utilizing wire-formed or machined pins which have been arranged as bandoliers
 
attached to conductive metal strips.
 
  
The core part of selective precious metal electroplating is the actual
+
These quality tests are performed according to industry standards, internal standards and customer specifications resp.
electroplating cell. In it the anode is arranged closely to the cathodic polarized
 
material strip. Cathode screens or masks may be applied between the two to
 
focus the electrical field onto closely defined spots on the cathode strip.
 
  
Special high performance electrolytes are used in selective electroplating to
+
==<!--7.3-->Comparison of Deposition Processes==
reach short plating times and allow a high flow rate of the electrolyte for a fast
+
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.
electrolyte exchange in the actual coating area.
 
  
For a closely targeted electroplating of limited precious metal coating of contact
+
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
springs so-called brush-electroplating cells are employed ''(Fig. 7.1)''. The “brush”
+
applications.
or “tampon” consists of a roof shaped titanium metal part covered with a special
 
felt-like material. The metal body has holes in defined spots through which the
 
electrolyte reaches the felt. In the same spots is also the anode consisting of a
 
fine platinum net. The pre-stamped and in the contact area pre-formed contact
 
spring part is guided under a defined pressure over the electrolyte soaked felt
 
material and gets wetted with the electrolyte. This allows the metal
 
electroplating in highly selective spots.
 
  
Fig. 7.1:
 
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,
+
<figtable id="tab:Comparison of different coating processes">
a dot shaped precious metal coating is required. This is achieved with two belt
+
<caption>'''<!--Table 7.7:-->Comparison of different coating processes'''</caption>
masks running synchronous to the carrier material. One of these two masks has
 
windows which are open to the spot areas targeted for precious metal plating
 
coverage.
 
  
===Summary of the processes for selective electroplating===
+
{| 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>
  
*'''Immersion electroplating'''
+
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.
Overall or selective electroplating of both sides of solid strips or pre-stamped
 
parts in strip form
 
  
*'''Stripe electroplating'''
+
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.
Stripe electroplating on solid strips through wheel cells or using masking
 
techniques
 
  
*'''Selective electroplating'''
+
==<!--7.4-->Hot (-Dipped) Tin Coated Strip Materials==
One-sided selective coating of solid, pre-stamped, or metallically belt-linked
+
During hot-dip tinning, pre-treated strip materials are coated with pure tin or tin alloys from a liquid solder metal. During overall (or all-around) tinning the strips through 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, also allows the production of thicker solder layers ( > 15 μm).
strips by brush plating
 
  
*'''Spot electroplating'''
+
The main advantage of hot tinning of copper and copper alloys, 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 the frictional force and mechanical wear in connectors. Tin coatings produced by hot tinning have a good adhesion to the substrate material and do not tend to tin whisker formation.
Electroplating in spots of solid strips with guide holes or pre-stamped parts in
 
strip form
 
  
===Typical examples of electroplated semi-finished materials===
+
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.
(overall or selectively)
+
The properties of these reflow tin coatings are comparable to those created by conventional hot tinning.
bild
 
  
 +
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'''
 
*'''Materials'''
 
+
Coating materials: Pure tin, tin alloys<br>
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s8">Type of Coatings</p></td><td><p class="s8">Coating Thickness</p></td><td><p class="s8">Remarks</p></td></tr><tr><td><p class="s8">Precious Metals</p></td><td/><td/></tr><tr><td><p class="s8">Pure gold</p><p class="s8">Hard gold (AuCo 0.3)</p></td><td><p class="s8">0.1 - 3 µm</p></td><td><p class="s8">In special cases up to 10 µm</p></td></tr><tr><td><p class="s8">Palladium-nickel (PdNi20)</p></td><td><p class="s8">0.1 - 5 µm</p></td><td><p class="s8">Frequently with additional 0.2 µm AuCo 0.3</p></td></tr><tr><td><p class="s8">Silver</p></td><td><p class="s8">0.5 - 10 µm</p></td><td><p class="s8">In special cases up to 40 µm</p></td></tr><tr><td><p class="s8">Non-precious Metals</p></td><td/><td/></tr><tr><td><p class="s8">Nickel</p></td><td><p class="s8">0.5 - 4 µm</p></td><td><p class="s8">Diffusion barrier especially for gold layers</p></td></tr><tr><td><p class="s8">Copper</p></td><td><p class="s8">1 - 5 µm</p></td><td><p class="s8">Intermediate layer used in tinning of CuZn</p></td></tr><tr><td><p class="s8">Tin, tin alloys</p></td><td><p class="s8">0.8 - 25 µm</p></td><td><p class="s8">materials</p></td></tr></table>
+
Substrate materials: Cu, CuZn, CuNiZn, CuSn, CuBe and others<br />
 
 
*'''Carrier Materials'''
 
Copper, copper alloys, nickel, nickel alloys, stainless steel
 
  
 
*'''Dimensions and Tolerances'''
 
*'''Dimensions and Tolerances'''
 +
{| class="twocolortable" style="text-align: left; font-size: 12px;width:40%"
 +
|-
 +
|Width of tinning:   
 +
|&#8805; 3 &#177; 1 mm
 +
|-
 +
|Thickness of tinning:   
 +
|1 - 15 μm
 +
|-
 +
|Tolerances (thickness):
 +
|&#177; 1 - &#177; 3 μm depending on tin thickness
 +
|}
  
Bild
+
*'''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.
  
Dimensions
+
==<!--7.5-->Contact Lubricants==
Carrier thickness d= 0.1 - 1 mm
+
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.
Carrier width B= 6 - 130 mm
 
Distance b > 2 mm
 
Coating width a= 2 - 30mm
 
Coating thickness s = 0.2 - 5 μm
 
(typical range)
 
Distance from edge b > 0.5 mm
 
depending on the carrier thickness
 
and the plating process
 
  
*'''Tolerances'''
+
Contact lubricants have to fulfill a multitude of technical requirements:
Coating thickness approx. 10 %
 
Coating thickness and position + 0,5 mm
 
  
*'''Quality Criteria'''
+
*They must wet the contact surface well; after the sliding operation the lubrication film must close itself again, i.e. mechanical interruptions to heal
Mechanical properties and dimensional tolerances of the carrier materials follow
+
*They should not transform into resins, not evaporate, and not act as dust collectors
the typical standards, i.e. DIN EN 1652 and 1654 for copper and copper alloys.
+
*The lubricants should not dissolve plastics, they should not be corrosive to non-precious metals or initiate cracking through stress corrosion of plastic components
Depending on the application the following parameters are tested and
+
*The specific electrical resistance of the lubricants cannot be so low that wetted plastic surfaces lose their isolating properties
recorded (see also: Electroplating of parts):
+
*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
  
*Coating thickness  *Solderability
+
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.
*Adhesion strength  *Bonding property
 
*Porosity          *Contact resistance
 
  
These quality tests are performed according to industry standards, internal
+
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 which differ in their chemical composition and viscosity.
standards, and customer specifications resp.
 
  
===7.1.2 Electroless Plating===
+
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.
  
===7.1.2.1 Introduction===
 
Electroless plating is defined as a coating process which is performed without
 
the use of an external current source. It allows a uniform metal coating
 
independent of the geometrical shape of the parts to be coated. Because of the
 
very good dispersion capability of the used electrolytes also cavities and the
 
inside of drilled holes in parts can be coated for example.
 
In principal two different mechanisms are employed for electroless plating:
 
processes in which the carrier material serves as a reduction agent (Immersion
 
processes) and those in which a reduction agent is added to the electrolyte
 
(Electroless processes).
 
  
===7.1.2.2 Immersion Processes===
+
==<!--7.6-->Passivation of Silver Surfaces==
The immersion processes are usually applied in the plating of the metals gold,
+
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 applied contact force.
silver, and tin. If the material to be coated is less precious, i.e. exhibits a
+
<figure id="fig:Typical process flow for the SILVERBRITE W ATPS process">
negative standard potential against the metal ions in the surrounding solution, it
+
[[File:Typical process flow for the SILVERBRITE W ATPS process.jpg|right|thumb|Figure 4: Typical process flow for the SILVERBRITE W ATPS process]]
goes into solution releasing electrons while the more precious metal ions are
+
</figure>
reduced by absorbing electrons and being deposited on the electrode. This
+
The passivation process SILVERBRITE W ATPS is a water-based tarnish preventer for silver (<xr id="fig:Typical process flow for the SILVERBRITE W ATPS process"/>). It is free of chromium(VI) compounds and solvents. The passivating layer is applied by immersion, which creates a transparent organic protective film which barely changes the appearance and only slightly
process can continue until the complete surface of the substrate is covered
+
increases the good electrical properties such as for example the contact resistance. The good solderability and bond properties of silver are not
with a thin layer of the more precious metal. This limits the maximum achievable
+
negatively affected. Because of its chemical composition, this protective layer has some lubricating properties which reduce the insertion and withdrawal forces of connectors noticeably.
layer thickness to approx. 0.1 μm ''(Table 7.5)''.
 
  
Table 7.5: Immersion Gold Electrolytes
+
==References==
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s8">Type of Electrolyte</p></td><td><p class="s8">pH-Range</p></td><td><p class="s8">Coating Properties</p></td><td><p class="s8">Application Ranges</p></td></tr><tr><td><p class="s8">Type of Electrolyte</p></td><td><p class="s8">pH-Range</p></td><td><p class="s8">Hardness</p><p class="s8">HV 0.025</p></td><td><p class="s8">Punity</p></td><td><p class="s8">Application Ranges</p></td></tr><tr><td><p class="s8">Immersion Gold electrolytes</p></td><td/><td/><td/><td/></tr><tr><td><p class="s8">AUROL 4</p><p class="s8">AUROL 16</p><p class="s8">AUROL 20</p></td><td><p class="s8">3.8 - 4.2</p><p class="s8">5.8 - 6.2</p><p class="s8">5.8 - 6.2</p><p class="s8">5.8 - 6.2</p></td><td><p class="s8">60 - 80</p><p class="s8">60 - 80</p><p class="s8">60 - 80</p><p class="s8">60 - 80</p></td><td><p class="s8">99.99% Au</p><p class="s8">99.99% Au</p><p class="s8">99.99% Au</p><p class="s8">99.99% Au</p></td><td><p class="s8">Thin gold layers on Ni, Ni alloys,</p><p class="s8">Fe and Fe alloys for PCB technology and technical applications</p></td></tr></table>
 
  
===7.1.2.3 Electroless Processes===
+
Vinaricky, E. (Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
The electroless metal plating with adding reduction agents to the electrolyte is
+
Springer-Verlag, Heidelberg 2002
based on the oxidation of the reducing agent with release of electrons which
 
then in turn reduce the metal ions. To achieve a controlled deposition from such
 
solutions the metal deposition has to happen through the catalytic influence of
 
the substrate surface.
 
  
Otherwise a “wild” uncontrollable deposition would occur. In most cases
+
Ganz, J.; Heber, J.; Macht, W.; Marka, E.: Galvanisch erzeugte
palladium containing solutions are used for the activation which seed the
+
Edelmetallschichten für elektrische Kontakte. Metall 61 (2007) H.6, 394-398
surfaces with palladium and act as catalysts in the copper and nickel
 
electrolytes.
 
  
The electrolytes contain besides the complex ion compounds of the metals to
+
Song, J.: Edelmetalle in Steckverbindungen - Funktionen und Einsparpotential.
be deposited also stabilizers, buffer and accelerator chemicals, and a suitable
+
VDE - Fachbericht 67 (2011) 13-22
reduction agent.
 
  
These electrolytes are usually operating at elevated temperatures (50° – 90°C).
+
Heber, J.: Galvanisch abgeschiedene Rhodiumschichten für den dekorativen
The deposits contain besides the metals also process related foreign inclusions
+
Bereich. Galvanotechnik, 98 (2007) H.12, 2931-2935
such as for example decomposition products of the reduction agents.
 
The electroless processes are used mainly for copper, nickel, and gold
 
deposits.
 
  
===7.1.2.4 Electroless Deposition of Nickel/Gold===
+
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
  
Electroless deposited nickel coatings with an additional immersion layer of gold
+
Grossmann, H. Schaudt, G.: Untersuchung über die Verwendbarkeit von
are seeing increased importance in the coating of printed circuit boards (PCBs).
+
Überzügen der Platinmetallgruppe auf elektrotechnischen Verbindungselementen.
The process sequence is shown in ''(Fig. 7.2)'' using the example of the
+
Galvanotechnik 67 (1976) 292-297
DODUCHEM process.
 
  
Tabelle
+
Grossmann, H.; Vinaricky, E.: Edelmetalleinsparung in der Elektrotechnik durch
 +
selektives Galvanisieren. In: Handbuch der Galvanotechnik. München, Hanser-
 +
Verlag, 37 (1981) 132-141
  
After the pre-cleaning (degreasing and etching) a palladium sulfate activator is
+
Grossmann, H.; Schaudt, G.: Hochgeschwindigkeitsabscheidung von Edelmetallen
used which activates the exposed copper surfaces on the printed circuit board
+
auf Kontaktwerkstoffen. Galvanotechnik 84 (1993) H.5, 1541-1547
and thus facilitates the nickel deposition. The electroless working chemical
 
nickel electrolyte contains – besides other ingredients – Sodium-hypophosphite,
 
which is reduced to phosphorus in a parallel occurring process and
 
incorporated into the nickel deposit. At the temperature of 87 – 89°C a very
 
homogeneous nickel-phosphorus alloy layer with approx. 9 wt% P is deposited
 
with layer thicknesses > 5 μm possible. During a consecutive processing step
 
a very thin and uniform layer (< 0.1 μm) of gold is added in an immersion
 
electrolyte. This protects the electroless nickel layer against corrosion achieving
 
a solderable and well bondable surface for thick or fine aluminum bond wires.
 
  
It is possible to enhance this layer combination further by adding a immersion
+
Bocking, C.; Cameron, B.: The Use of High Speed Selective Jet
palladium layer between the electroless nickel and the gold coating
+
Electrodeposition of Gold for the Plating of Connectors. Trans. IMF. 72 (1994)
(DODUBOND process). This Pd layer acts as a diffusion barrier and allows the
+
33-40
usage of this surface combination also for gold wire bonding.
 
  
As an alternative, for gold wire bonding applications a thicker gold layer of 0.2 –
+
Endres, B.: Selektive Beschichtungen von Kontaktmaterial im
0.5 μm can be applied using an electroless process. Typical electrolytes work at
+
Durchzugsverfahren. Metalloberfläche 39 (1985) H.11, 400-404
a temperature of approx. 80°C with deposition rates of 0.3 – 0.4 μm per 30
 
minutes. There are however limitations with these electroless electrolytes
 
concerning their stability and the robustness of the process compared to other
 
electroplating processes which reduces their wider usage ''(Fig. 7.3)''.
 
  
Fig. 7.3:
+
Kaspar, F.; Marka, E.; Normann, N.: Eigenschaften von chemisch Nickel
Coating composition
+
Goldschichten für Baugruppen der Elektrotechnik.
of a printed circuit board with
+
VDE Fachbericht 47 (1995) 19-27
reductively enhanced gold
 
  
===7.1.2.5 Immersion Deposition of Tin===
+
Schmitt; W.; Kißling, S.; Behrens, V.: Elektrochemisch hergestellte
A tin coating by ion exchange is usually not possible since copper is the more
+
Schichtsysteme auf Aluminium für Kontaktanwendungen.
precious metal. By adding thio-urea the electro-chemical potential of copper is
+
VDE - Fachbericht 67 (2011) 136-141
reduced to a level (approx. 450 mV, significantly lower than tin) that allows the
 
exchange reaction. Using a suitable electrolyte composition and enhancer
 
solutions like with the DODUSTAN process ''(Fig. 7.4)'' tin coatings can be
 
produced that, even under usually unfavorable conditions of copper
 
concentrations of 7 g/l in the electrolyte, are well solderable.
 
  
Fig. 7.4: Process flow for electroless tin deposition using the DODUSTAN process
+
Freller, H.: Moderne PVD-Technologien zum Aufbringen dünner
 +
Kontaktschichten. VDE-Fachbericht 40 (1989) 33-39
  
The immersion tin deposition is suitable for the production of a well solderable
+
Ganz, J.: PVD-Verfahren als Ergänzung der Galvanik. Metalloberfläche 45 (1991)
surface on printed circuit boards and electronic components. It is also used as
 
an etch resist against ammonia based solutions or as corrosion and oxidation
 
protection of copper surfaces.
 
  
===7.2 Coatings from the Gaseous Phase (Vacuum Deposition)===
+
Schmitt, W.; Franz, S.; Heber, J.; Lutz, O.; Behrens, V.: Formation of Silver
The term PVD (physical vapor deposition) defines processes of metal, metal
+
Sulfide Layers and their Influence on the Electrical Characteristics of Contacts in
alloys, and chemical compounds deposition in a vacuum by adding thermal and
+
th the Field of Information Technology. Proc. 24 Int. Conf.on Electr. Contacts,
kinetic energy through particle bombardment. The main processes are the
+
Saint Malo, France (2008) 489-494
following four coating variations ''(Table 7.6)'':
 
  
*Vapor deposition    *Sputtering (Cathode atomization)
+
Buresch, I; Ganz, J.; Kaspar, F.: PVD-Beschichtungen und ihre Anwendungen
*Arc vaporizing      *Ion implantation
+
für Steckverbinder. VDE-Fachbericht 59 (2003) 73-80
  
In all four processes the coating material is transported in its atomic form to the
+
Gehlert, B.: Edelmetalllegierungen für elektrische Kontakte.
substrate and deposited on it as a thin layer (a few nm to approx. 10 μm)
+
Metall 61 (2007) H.6, 374-379
  
Table 7.6: Characteristics of the Most Important PVD Processes
+
Ganz, J.: Einsatz von Sputterverfahren bei komplexen
 +
Beschichtungsaufgaben. JOT 11 (1997)
  
tabelle fehlt!
+
Buresch, I.; Bögel, A.; Dürrschnabel, W.: Tin Coating for Electrical Components.
 +
Metall 48 (1994) H.1, 11-14
  
The sputtering process has gained the economically most significant usage. Its
+
Buresch, I.; Horn, J.: Bleifreie Zinnoberflächen.
process principle is illustrated in ''(Fig. 7.5)''.
+
VDE-Fachbericht 61 (2005) 89-94
  
Fig. 7.5: Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms
+
Adler, U.; Buresch, I.; Riepe, U.; Tietz, V.: Charakteristische Eigenschaften der
 +
schmelzflüssigen Verzinnung von Kupferwerkstoffen.
 +
VDE-Fachbericht 63 (2007) 175-180
  
Initially a gas discharge is ignited in a low pressure (10 – 1 Pa) argon
+
Huck, M.: Einsatz von Schmiermitteln auf Gleit- und Steckkontakten.
atmosphere. The argon ions generated are accelerated in an electric field and
+
Metalloberfläche (1982) 429-435
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
+
Abbott, W.,H.: Field and Laboratory Studies of Corrosion Inhibiting Lubricants
contact applications are:
+
for Gold-Plated Connectors. Proc. HOLM Conf.on Electrical Contacts, Chicago
 +
(1996) 414-428
  
*High purity of the deposit layers  *Low thermal impact on the
+
Noel, S.; Alarmaguy, D.; Correia, S.; Gendre, P.: Study of Thin Underlayers to
*Almost unlimited coating materials  substrate
+
Hinder Contact resistance Increase Due to Intermetallic Compound Formation.
*Low coating thickness tolerance    *Excellent adhesion (also by using additional intermediate layers)
+
th Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, BC,
 +
Canada (2009) 153 – 159
  
Coatings produced by PVD processes are used for contact applications, for
+
Weik, G.; Johler, W.; Schrank, C.: Zuverlässigkeit und Eigenschaften von Gold –
example on miniature-profiles, in electrical engineering and for electronic
+
Schichten bei hohen Einsatztemperaturen.
components, for solderability in joining processes, for metalizing of nonconductive
+
VDE – Fachbericht 65, (2009) 13 – 21
materials, as well as in semiconductors, opto-electronics, optics,
 
and medical technology applications.
 
  
There are few limitations regarding the geometrical shape of substrate parts.
+
Buresch, I.; Hack, M.: Eigenschaften von Zinnschichten für elektromechanische
Only the interior coating of drilled holes and small diameter tubing can be more
+
Bauelemente – Einflussfaktoren und ihre Auswirkungen. VDE – Fachbericht 65,
problematic (ratio of depth to diameter should be < 2:1). Profile wires, strips,
+
(2009) 23 – 30
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'''
+
Buresch, I.: Effekte intermetallischer Phasen auf die Eigenschaften von
bild
+
Zinnoberflächen auf Kupferlegierungen. VDE – Fachbericht 67 (2011) 38-46
  
*'''Materials'''
+
Schmitt, W.; Heber, J.; Lutz, O.; Behrens, V.: Einfluss des Herstellverfahrens auf
Selection of possible combinations of coating and substrate materials
+
das Korrosions- und Kontaktverhalten von Ag – Beschichtungen in
<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s8">Substrate Materials</p></td><td><p class="s8">Coating Materials</p></td></tr><tr><td><p class="s8">Substrate Materials</p></td><td><p><span><IMG width="13" height="12" src="KAPITEL 7 englisch/Image_035.png"/></span></p></td><td><p><span><IMG width="13" height="10" src="KAPITEL 7 englisch/Image_036.png"/></span></p></td><td><p><span><IMG width="10" height="10" src="KAPITEL 7 englisch/Image_037.png"/></span></p></td><td><p><span><IMG width="13" height="10" src="KAPITEL 7 englisch/Image_038.png"/></span></p></td><td><p><span><IMG width="14" height="10" src="KAPITEL 7 englisch/Image_039.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_040.png"/></span></p></td><td><p><span><IMG width="8" height="10" src="KAPITEL 7 englisch/Image_041.png"/></span></p></td><td><p><span><IMG width="12" height="10" src="KAPITEL 7 englisch/Image_042.png"/></span></p></td><td><p><span><IMG width="15" height="10" src="KAPITEL 7 englisch/Image_043.png"/></span></p></td><td><p><span><IMG width="11" height="10" src="KAPITEL 7 englisch/Image_044.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_045.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_046.png"/></span></p></td></tr><tr><td><p class="s8">Precious metal / alloys</p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_047.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_048.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_049.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_050.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_051.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_052.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_053.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_054.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_055.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_056.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_057.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_058.png"/></span></p></td></tr><tr><td><p class="s8">NF metals / alloys</p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_059.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_060.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_061.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_062.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_063.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_064.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_065.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_066.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_067.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_068.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_069.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_070.png"/></span></p></td></tr><tr><td><p class="s8">Fe alloys / stainless steel</p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_071.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_072.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_073.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_074.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_075.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_076.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_077.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_078.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_079.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_080.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_081.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_082.png"/></span></p></td></tr><tr><td><p class="s8">Special metals (Ti, Mo, W)</p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_083.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_084.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_085.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_086.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_087.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_088.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_089.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_090.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_091.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_092.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_093.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_094.png"/></span></p></td></tr><tr><td><p class="s8">Carbide steels (WC-Co)</p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_095.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_096.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_097.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_098.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_099.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_100.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_101.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_102.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_103.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_104.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_105.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_106.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><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_107.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_108.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_109.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_110.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_111.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_112.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_113.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_114.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_115.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_116.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_117.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_118.png"/></span></p></td></tr><tr><td><p class="s8">Glasses (SiO<span class="s16">2</span>, CaF)</p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_119.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_120.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_121.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_122.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_123.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_124.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_125.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_126.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_127.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_128.png"/></span></p></td><td><p><span><IMG width="9" height="10" src="KAPITEL 7 englisch/Image_129.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_130.png"/></span></p></td></tr><tr><td><p class="s8">Plastics (PA, PPS)</p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_131.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_132.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_133.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_134.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_135.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_136.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_137.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_138.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_139.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_140.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_141.png"/></span></p></td><td><p><span><IMG width="8" height="8" src="KAPITEL 7 englisch/Image_142.png"/></span></p></td></tr></table>
+
schwefelhaltiger Umgebung. VDE – Fachbericht 65 (2009) 51 – 58
  
*'''Dimensions'''
+
[[de:Beschichtungsverfahren]]

Latest revision as of 14:37, 26 January 2023

Besides manufacturing contact materials from the solid phase, i.e. by melt or powder metallurgy, the production starting in the liquid or gaseous phase is generally preferred when thin layers within the μm range are required, which cannot be obtained economically by conventional cladding methods (Table 1). Such coatings fulfill different requirements depending on their composition and thickness. They can serve as corrosion or wear protection or can fulfill the need for thin contact layers for certain technical applications. In addition they serve for decorative purposes as a pleasing and wear resistant surface coating.

Table 1: Overview of Important Properties of Electroplated Coatings and their Applications
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 *) 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
*) Coercive force= force to retaim the adopted magnetisation

To reduce the mechanical wear of thin surface layers on sliding and connector contacts, 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 used differentiated by the metallic deposition being performed either with or without the 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 pieces as the cathode, forces the positively charged metal ions to move to the cathode where they give up their charge and deposit themselves as metal on the surface of the work piece. Depending on the application, for electric and electronic or decorative end use, different electrolytic bath solutions (electrolytes) are used. The electroplating equipment 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 important parameter for creating strongly adhering deposits is that the surface of the goods has to be metallic clean without oily or oxide film residues. This is achieved through various pre-treatment processes, specifically developed for the types of material and surface conditions of the goods to be plated. In the following segments, electrolytes – both precious and non-precious – as well as the most widely used electroplating processes are described.

Main Articel: Electroplating (or Galvanic Deposition)

Electroless Plating

Electroless plating is defined as a coating process which is performed without the use of an external current source. It allows a uniform metal coating, independent of the geometrical shape of the parts, to be coated. Because of the very good dispersion capability of the used electrolytes, also cavities and the inside of drilled holes in parts can be coated for example. In principal, two different mechanisms are employed for electroless plating: processes in which the carrier material serves as a reduction agent (Immersion processes) and those in which a reduction agent is added to the electrolyte (Electroless processes).

Main Articel: Electroless Plating

Coatings from the Gaseous Phase (Vacuum Deposition)

The term PVD (physical vapor deposition) defines processes of metal, metal alloys and chemical compounds deposition in a vacuum by adding thermal and kinetic energy by particle bombardment. The main processes are the following four coating variations (Table 2):

  • 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)


Table 2: Characteristics of the Most Important PVD Processes
Process Principle Process Gas Pressure Particle Energy Remarks
Vapor deposition Vaporizing in a crucible
(electron beam or resistance heating)
10-3 Pa < 2eV Separation of alloy components may occur
Arc vaporizing Vaporizing of the target
plate in an electrical arc
10-1 Pa-1Pa 80eV-300eV Very good adhesion due to ion bombardement
Sputtering Atomizing of the target plate
(cathode) in a gas discharge
10-1 Pa-1Pa 10eV-100eV Sputtering of non-conductive materials possible through RF operation
Ion implantation Combination of vapor
deposition and sputtering
10-1 Pa-1Pa 80eV-300eV Very good adhesion from ion bombardment but also heating of the substrate material


The sputtering process has gained the economically most significant usage. Its process principle is illustrated in (Figure 1).

Figure 1: Principle of sputtering Ar = Argon atoms; e = Electrons; M = Metal atoms

Initially, a gas discharge is ignited in a low pressure (10-1 -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 (Figure 2).

Figure 2: Examples of vacuum coated semi finished materials and parts


  • Materials

Selection of possible combinations of coating and substrate materials

Substrate Materials

Coating Materials

Ag

Au

Pt

Pd

Cu

Ni

Ti

Cr

Mo

W

Ai

Si

Precious metal / alloys

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

NF metals / alloys

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

Fe alloys / stainless steel

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

Special metals (Ti, Mo, W)

K7-leer.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-leer.png

K7-gef.png

Carbide steels (WC-Co)

K7-leer.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-leer.png

K7-gef.png

Ceramics (Al2O3, AlN)

K7-leer.png

K7-leer.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-leer.png

K7-gef.png

Glasses (SiO2, CaF)

K7-leer.png

K7-leer.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-leer.png

K7-gef.png

Plastics (PA, PPS)

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png

K7-gef.png can be produced K7-leer.png can be produced with intermediate layer

  • Dimensions
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.

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. Table 3 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.


Table 3: Comparison of different coating processes
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
(in special cases up to 100 μm)
0.1 approx. 10 μm
Coating configuration selectively, stamping edges not coated all around and selectively
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

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.

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 strips through 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, also allows the production of thicker solder layers ( > 15 μm).

The main advantage of hot tinning of copper and copper alloys, compared to tin electroplating, is the formation of an inter-metallic copper-tin phase (Cu3Sn, Cu6Sn5) at the boundary between the carrier material and the tin layer. This thin (0.3 – 0.5 μm) intermediate layer, which is formed during the thermal tinning process, is rather hard and reduces the frictional force and mechanical wear in connectors. 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 (Figure 3).

Figure 3: Typical examples of hot tinned strip materials


  • Materials

Coating materials: Pure tin, tin alloys
Substrate materials: Cu, CuZn, CuNiZn, CuSn, CuBe and others

  • Dimensions and Tolerances
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.

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 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.


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 applied contact force.

Figure 4: Typical process flow for the SILVERBRITE W ATPS process

The passivation process SILVERBRITE W ATPS is a water-based tarnish preventer for silver (Figure 4). 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.

References

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