Electroplating is a method of coating one metal with some other by electrolysis. This procedure is carried out using traditional diving techniques. After preliminary preparation, the printed circuit boards are loaded into a galvanic bath, which is a container made of a dielectric, which is filled with an electrolyte and equipped with anodes (they can be soluble and insoluble), as well as a device for maintaining the temperature and mixing the solution.
Board Processing
Passing direct current leads to the fact that the areas of the board uncovered with a protective mask and connected to the electrode are covered with a layer of nickel or gold of a certain thickness. Correct positioning of the anodes ensures that the coating thickness is approximately uniform.
Gilding of printed circuit boards is usually done using a two-step process. First they are immersed in a bath, where nickel is applied in a galvanic manner. In this case, a high current density is used, due to which a nickel layer is deposited from the acid solution, the thickness of which is 0.05-0.1 microns. This ensures a strong adhesion of nickel and copper, which reduces the porosity of the coating and also prevents the penetration of copper into the gold layer. After washing, the products are usually transferred to a gilding bath, where a layer of gold is built up to 0.5 microns from the electrolyte.
Electroplating and decoration
Already in ancient times there was a decorative finish of art metals. Modern production suggests that galvanic processing will be used to give some special properties to the metal surface. Protective coatings of noble metals can be obtained by the deposition of metals from salt solutions under the influence of electric current. Thanks to such coatings, it is possible to preserve the color and luster of jewelry for quite a long time. They not only prevent darkening of products, but also have an excellent polishing effect. For example, plating with gold or silver allows you to permanently preserve the color and luster of jewelry.
There are several different options for this process, each of which involves the use of a particular metal:
- chrome plating;
- copper plating;
- galvanizing;
- nickel plating;
- tin-bismuth coating;
- chemical oxidation;
- chemical passivation;
- anodizing;
- electropolishing.
Chrome plating
This is diffuse saturation of the steel surface with chromium or deposition on a part of a layer of a substance from an electrolyte under the influence of an electric current. In this case, electroplating is focused on corrosion protection; it is used to decorate or to increase the degree of surface hardness. Chrome plating in industry can also be used for decoration. In this case, the main goal of the procedure is to give the metal surface a beautiful, effective shine. The part must be polished before applying chromium.
Coating properties
Hard chrome plating is characterized by heat resistance, a high degree of wear resistance, poor wettability, low coefficient of friction, and also low ductility. In addition, the surface receives properties such as stability in terms of friction, the ability to withstand the distribution load, as well as the disadvantage associated with the ease of destruction under the action of concentrated shock loads. The galvanic coating in the form of milk chromium has a low degree of wear resistance and hardness, low porosity. The surface is protected against corrosion while maintaining an attractive decorative look.
The use of chromium plating in industry
The main purpose with which it is used in industry is to impart details such as increased wear resistance, increased corrosion resistance, and reduced friction. Thanks to this process, steel becomes stronger, does not undergo gas corrosion, and also does not collapse in sea and ordinary water, nitric acid. The galvanic coating of this type leads to the fact that surface defects become only more significant, which is why it is necessary to carry out subsequent processing, since in this case there is no leveling effect.
Copper plating
The use of copper coatings is relevant in cases where it is necessary to increase the electrical conductivity, and they are also used as an intermediate layer on steel products before chromium, nickel or other coatings are applied. So it is possible to provide better grip, as well as increase the protective ability. Electroplated copper coating is usually not used as an independent or decorative. Due to the fact that this metal is able to prevent the formation of sparks, the product can be used in the oil and gas industry.
Application of copper plating
This process is used for coating copper on steel products or on steel wire. Often, this type of coating is used to protect individual sections of steel products from cement, and those areas that are supposed to be further processed are processed.
Electroplating coatings of metals in this case are often used in the oil and gas industry to prevent the formation of sparks, in the electric power industry for the subsequent application of multilayer coatings intended for protection and decoration, in the manufacture of printed circuit boards, to improve soldering, and much more. The surface takes on a color from light pink to dark red. Shades are usually not standardized.
Galvanizing
One of the most common methods for protecting metal products is galvanizing. It is usually used to process a variety of alloyed or carbon steel grades. The application of galvanic coatings of this type is in demand enough to protect wire products and fasteners. Once in a humid environment, the zinc surface acts as an anode, due to which oxidative reactions are slowed down, and the base metal thus receives reliable protection against negative environmental factors.
Electroplating of this type can be used only after metal products are processed in a special way. To do this, they should be cleaned of rust, scale, technical equipment lubricating and cooling purposes. When the galvanizing process is completed, the product must undergo clarification, that is, it is etched with a weak solution of nitric acid, after which passivation is carried out. So, not only is it possible to increase the resistance of galvanized products to negative factors, but also to make them more decorative, that is, to give shine and a certain shade. The technology of electroplating in this case involves the thickness of the zinc layer from 6 microns to 1.5 mm.
Nickel plating
Protection of metal products can be carried out using various technologies. One of the most popular and common at the moment is nickel plating. This popularity is due to the chemical properties of nickel. It has a high degree of corrosion resistance in the aquatic environment, and nickel oxide prevents the subsequent oxidation of the metal. In addition, nickel is slightly susceptible to salts, acids and alkalis, with the exception of nitric acid. For example, an electroplated coating with a thickness of 0.125 mm protects against most industrial gases, characterized by increased aggressiveness. Such a moment is also very important: almost all metals lend themselves to nickel, so this method can be used for additional processing of products.
The use of nickel is appropriate for a number of tasks:
- ensuring the protection of metal products;
- use as a decorative coating;
- the formation of a preliminary layer, which will be subjected to further processing;
- restoration of parts and assemblies.
The coating is characterized by increased wear resistance and hardness and is recommended for parts that work in friction conditions, especially in the absence of any lubricant, used to protect against corrosion, as well as to ensure high-quality soldering of low-temperature solders, all of which are prescribed in GOST. Galvanic coatings are highly fragile, therefore, it is not recommended to flare and bend parts that have undergone nickel plating. It is recommended for complex parts. After the heat treatment procedure at a temperature of 400 degrees Celsius, the coating acquires maximum hardness.
Tin-Bismuth
Tin coating is resistant to sulfur compounds, therefore it is recommended for parts that are in contact with rubber and plastics. Among its properties can be called excellent adhesion to the base metal, elasticity, the ability to bend, stretch, stamping, flaring, press fit, as well as good retention during make-up. Freshly deposited tin coating solders well.
conclusions
Electroplating allows you to improve the conductive characteristics of parts, giving them excellent properties of electrical insulation, as well as protecting them from the effects of various substances. In addition, this method allows to obtain excellent surfaces having a mirror appearance, as well as simulating an enamel coating. It is difficult to overestimate how important electroplating is in modern production, since the development of technology has made it possible to make the process more advanced.