The application of chemically deposited coatings can be divided into two groups. For the metallization of decorative plastics, a thin layer of metal (0.3 to 1.0 μm) is deposited chemically on the upper surface of a dielectric , and its thickness is then increased by electroplating techniques. In this case, the properties of the electroless deposited coating and the nature of the metal are not important; it is only important to ensure that such coatings are dense and sufficiently conductive for subsequent electroplating and to provide the metal layer required. required adhesion. Metal selective deposition for chemical underlayers is for process convenience and cost. For this, coatings are used for nickel and copper. Nickel is more convenient because electroless nickel solutions are more stable and their composition is simpler than similar electroless copper solutions.
Adhesion of a coating to a non-conductive surface is primarily determined by the state of the coating surface, whereas the nature of the metal (at least for nickel and copper) is generally responsible for adhesion. Copper coatings may be preferred due to their higher conductivity. A copper bottom layer is almost always used in the production of printed circuit boards.
On the other hand, chemically deposited finished coatings are thicker and their usefulness depends on their mechanical, electrical and magnetic properties. Very popular are nickel (Ni-P and Ni-B) coatings deposited on metal products. The 20 to 30 μm thick copper coating deposited on the plastic has good electrical conductivity and ductility, so it can be used in the production of printed circuit boards made by additive processes. The entire circuit pattern is obtained by electroless plating technology. Coatings of cobalt and its alloys can be used to exploit their specific magnetic properties; silver and gold coatings are used because of their good electrical conductivity, optical properties and inertness.
Electroless plating can be performed by using the plating solution once (until any components in the solution are consumed and the reaction rate drops sharply) or by replenishing the species consumed during the plating process. The long-term development of solutions reduces the amount of plating waste and ensures higher labor productivity, but at the same time, it places stricter requirements on the plating baths: they need to be stable and their parameters should not change significantly over time. In addition, special equipment is required to monitor and control the composition of such solutions. For this reason, the long-term development of the solution is only suitable for large-scale production processes.
Disposable solutions are more versatile, but they are less economical and less efficient. One-time use However, when the solution has simple components and the basic components (metal ions first) are completely consumed during the electroplating process, while the remaining components (such as ligands) are inexpensive and will not pollute the environment. In this case, a single-use process is actually acceptable even in mass production. An extreme case of using a plating solution alone is an aerosol spray, where two drops
The solution starts spraying on or near the surface to be plated through a special Spray Gun. One solution usually contains metal ions, while the other contains a reducing agent. The metal ion reduction in this case should be fast enough to allow most of the metal to precipitate on the surface before the solution film runs off it. This method is suitable for the deposition of easily reducible metals such as silver and gold, although this aerosol solution is also used for the deposition of copper and nickel. The aerosol spray method is great for depositing thin coatings on large, flat surfaces: the process is similar to painting.
Since the components of electroless plating baths, firstly metal ions, can be toxic and polluting, techniques have been developed to recover metals from spent plating baths, as well as rinse water. Other valuable solution components such as ligands (EDTA, tartrate) can also be recovered.
Electroless plating usually does not require complex equipment. The plating bath solution needs to exhibit sufficient chemical inertness and its lining should not catalyze the deposition of metal.
Such tanks are usually made of chemically stable plastic; metal tanks can also be used—they can be made of stainless steel or titanium. In order to prevent possible deposits of metal on the walls, one suffices to apply a positive potential to them using a special current source (anodic protection). Plated parts can be mounted on racks; small parts can be placed in buckets immersed in plating solution. Filtration and filtration of the heated solution are performed in the same manner as in the electroplating process. Special Auto has developed equipment for monitoring and controlling the composition of plating solutions.