well as the most widely used electroplating processes are described.
Main Articel: [[Electroplating (or Galvanic Deposition)| Electroplating (or Galvanic Deposition)]]
==== Selective Electroplating====
Since precious metals are rather expensive it is necessary to perform the
electroplating most economically and coat only those areas that need the layers
for functional purposes. This leads from overall plating to selective
electroplating of strip material in continuous reel-to-reel processes. Depending
on the final parts design and the end application the processes can be applied
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
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
reach short plating times and allow a high flow rate of the electrolyte for a fast
electrolyte exchange in the actual coating area.
For a closely targeted electroplating of limited precious metal coating of contact
springs so-called brush-electroplating cells are employed ''(Fig. 7.1)''. The “brush”
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,
a dot shaped precious metal coating is required. This is achieved with two belt
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'''
*'''Immersion electroplating'''
Overall or selective electroplating of both sides of solid strips or pre-stamped
parts in strip form
*'''Stripe electroplating'''
Stripe electroplating on solid strips through wheel cells or using masking
techniques
*'''Selective electroplating'''
One-sided selective coating of solid, pre-stamped, or metallically belt-linked
strips by brush plating
*'''Spot electroplating'''
Electroplating in spots of solid strips with guide holes or pre-stamped parts in
strip form
'''Typical examples of electroplated semi-finished materials'''
(overall or selectively)
bild
*'''Materials'''
<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>
*'''Carrier Materials'''
Copper, copper alloys, nickel, nickel alloys, stainless steel
*'''Dimensions and Tolerances'''
Bild
Dimensions
Carrier thickness d= 0.1 - 1 mm
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'''
Coating thickness approx. 10 %
Coating thickness and position + 0,5 mm
*'''Quality Criteria'''
Mechanical properties and dimensional tolerances of the carrier materials follow
the typical standards, i.e. DIN EN 1652 and 1654 for copper and copper alloys.
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.
Main Articel: [[Electroplating (or Galvanic Deposition)| Electroplating (or Galvanic Deposition)]]