Changes

For the electroplating of metals, especially precious metals, and 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 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.

The actual metal deposition occurs in the electrolytic solution which contains the plating material as metal ions. Besides this basic ingredient, the electrolytes contain additional components depending on the processes used, such as for example conduction salts, brighteners, and organic additives which are codeposited into the coatings, influencing the final properties of the electroplating deposit.

All precious metals can be electroplated with silver and gold , also they are by far the most widely used ones <xr id="tab:Precious Metal Electrolytes for Technical Applications"/><!--(Tab. 7.2)--> and <xr id="tab:Precious Metal Electrolytes for Decorative Applications"/><!--(Tab. 7.3)-->.

*Gold electrolytes <br>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.<br />

*Palladium and Platinum electrolytes <br/> 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.<br />

*Ruthenium electrolytes <br>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.<br />

*Silver electrolytes <br>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.<br />

The most important non-precious metals that are deposited by electroplating are: Copper, nickel, tin, and zinc and as well as their alloys. The deposition is performed in the form of pure metals with different electrolytes used <xr id="tab:Typical Electrolytes for the Deposition of Non-Precious Metals"/><!--(Table 7.4)-->.

*Copper electrolytes <br>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.<br />

*Tin electrolytes <br>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.<br />

The complete or all-around electroplating of small mass produced parts , like contact springs, rivets, or pins is usually done as mass plating in electroplating barrels of different shape. During the electroplating process the parts are continuously moved and mixed to reach a uniform coating.

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, electroplatingor rinsing, 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 and wires. Compared to hard gold or palladium , these deposits are rather ductile, ensuring that during following stamping and forming operations , no cracks are generated in the electroplated layers.

Since precious metals are rather expensive , it is necessary to perform the electroplating most economically and to 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 Inside the cell, 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.

For a closely targeted electroplating of limited precious metal coating of contact springs , so-called brush-electroplating cells are employed <xr id="fig:Brush Tampon plating cell"/><!--(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. Also located 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.

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.

One-sided selective coating of solid, pre-stamped, or metallically belt-linked strips by brush plating

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):

These quality tests are performed according to industry industrial standards, internal standards, and customer specifications resp.