The difference between electroplating, electroforming, electrophoresis, sputtering and anodizing

The difference between electroplating, electroforming, electrophoresis, sputtering and anodizing

Electroplating is the process of plating a thin layer of another metal or alloy onto certain metal surfaces using the principle of electrolysis. The principle of electroplating is similar to that of electrolytic refining of copper. During electroplating, a plating solution is typically prepared using an electrolyte that contains ions of the plating metal. The metal object to be plated is immersed in the solution and connected to the negative terminal of a direct current (DC) power supply, acting as the cathode. The plating metal is used as the anode and connected to the positive terminal of the DC power supply. When a low-voltage DC current is applied, the anode metal dissolves into the solution, forming cations that migrate to the cathode. These ions gain electrons at the cathode and are reduced to their metallic form, which then deposits onto the surface of the metal object being plated.

Characteristics of electroplating:

The technology of depositing a metal coating with good adhesion but different performance from the base material on mechanical products is based on the principle of the electrolytic cell. Electroplating can enhance the corrosion resistance of metals (plating metals are mostly corrosion-resistant), increase hardness, prevent wear, and improve conductivity, smoothness, heat resistance, and surface appearance.

Through electroplating, decorative, protective, and various functional surface layers can be obtained on mechanical products. Additionally, workpieces with wear and processing errors can also be repaired.

Types of electroplating

1. Copper Plating: Used as a base coating to enhance the adhesion and corrosion resistance of the electroplating layer. (Note: Copper is prone to oxidation. Once oxidized, the resulting copper oxide is non-conductive. Therefore, copper-plated products must be protected from oxidation.)

2. Nickel Plating: Used as a base coating or for appearance to enhance corrosion resistance and wear resistance. (Modern chemical nickel plating offers wear resistance that exceeds that of chrome plating.) (Note: Many electronic products, such as DIN plugs and N plugs, no longer use nickel as a base coating. This is primarily because nickel is magnetic and can affect passive intermodulation in electrical performance.)

3. Gold Plating: Improves conductive contact impedance and enhances signal transmission. (Gold is the most stable and the most expensive plating material.)

4. Palladium-Nickel Plating: Improves conductive contact impedance and enhances signal transmission. It offers higher wear resistance than gold plating.

5. Tin-Lead Plating: Improves solderability. However, it is being quickly replaced by other substitutes (due to its lead content). Most applications now use bright tin or matte tin plating instead.

6. Silver Plating: Improves conductive contact impedance and enhances signal transmission. (Silver has the best performance among plating materials, but it is also prone to oxidation. Fortunately, oxidized silver remains conductive.)

Electroforming can be roughly divided into three categories: decorative electroplating (represented by nickel-chromium, gold, and silver), protective electroplating (represented by zinc plating), and functional electroplating (represented by hard chromium plating). Electroforming is one of the functional electroplating methods used to manufacture products.

It is said that electroforming began in 1838 and was mainly used for arts and crafts. At that time, Jacoli of Russia coated a gypsum master mold with wax, made the surface conductive through graphite, and then plated it with copper. After plating, the mold was demolded to produce a copper replica. In the early years of the Showa era in Japan, the Kyoto City Industrial Research Institute, the Osaka Mint Department, and other units actively carried out research on casting copper on gypsum molds and electroplating on insulators, producing many exquisite metal crafts. However, when using gypsum or wax as the master mold, electroforming required high manufacturing skills and complex operations. Additionally, the master mold was easily damaged, making it difficult to produce exquisite replicas. As a result, the application range of electroforming was very limited.

After a century of development, electroforming technology has been widely used in many fields, such as the light industry and electronics, especially in the manufacture of thin-walled, precise, or complex-shaped parts that are difficult to machine (such as metal foil, nozzles, waveguides, surface roughness measuring instruments, etc.) and molds (such as record molds, plastic molds, rubber molds, etc.). It has been highly valued as a cutting-edge processing technology.

Later, with the advent of plastic master materials and improvements in electroplating techniques, electroforming technology advanced significantly and was widely used to manufacture products that could not be produced by other methods or were difficult to process. In recent years, electroforming has attracted attention as a cutting-edge processing technology, particularly for manufacturing certain parts for aerospace or atomic energy applications. Additionally, the so-called "electric bonding technology," which joins metal to metal through electroplating, has been studied. This electrically bonded metal does not alter the mechanical or physical properties of the metal material due to heat.

Electroforming is the process of manufacturing or replicating metal products by electrodepositing metal onto a mold through electrolysis. The electroforming accuracy can reach 0.001 mm to 0.01 mm.

Features of Electroforming:

• High Fidelity Replication: Accurately and precisely replicates the mold surface, including fine details and lines.
• High Dimensional Accuracy and Surface Quality: Replicas with high dimensional accuracy can be obtained, with surface roughness less than 0.1 µm. Products produced from the same original mold exhibit good consistency.
• Complex Part Replication: With the help of special materials, the inner surfaces of complex parts can be replicated as outer surfaces, and vice versa. The replicated products are consistent with the original mold.

Electroforming is mainly used for:

1. Replicating fine surface contour patterns (such as record moulds, arts and crafts moulds, banknotes, securities, and stamp printing plates);

2. Replicating injection moulds and electrode tools for EDM;

3. Manufacturing complex, high-precision hollow parts and thin parts (such as waveguides, etc.)

4. Manufacturing surface roughness templates, reflectors, dials, special-shaped nozzles and other special parts.

At present, electroforming technology has attracted worldwide attention. Whenever difficulties arise in mechanical processing, electroforming technology can be applied to transform the inner surface of parts that are more difficult to process into the outer surface of the core mould and to transform metal materials that are difficult to form into core mould materials that are easy to form (such as wax, resin, plastic, etc.). This makes electroforming a cutting-edge processing technology that is generally applicable to the machinery industry. Electroforming is widely used in mechanical processing bodies, precision optical instruments, rocket engines, chemicals, radars, and laser waveguides, and can electroformed metal lines below 0.5um on large workpieces.

The metals that can be electroformed now include copper, nickel, nickel-cobalt alloy, iron, nickel-manganese alloy, etc. The products processed by electroforming mainly include waveguides, wind tubes, ventures, supersonic gas cutting nozzles, metal foils, screens, printing and dyeing rollers, record stamps, plastic or rubber parts die cavity, bellows, wind tunnel nozzle inner wall, rocket engine regenerative cooling thrust chamber outer wall, etc.

The electroformed copper layer has good electrical conductivity and thermal conductivity and is mainly used in occasions requiring good electrical and thermal conductivity, such as waveguides, supersonic gas cutting tubes, and the main body outer layer of plastic or rubber moulding moulds.

Electroformed nickel has high strength and hardness, good corrosion resistance and is often used as a structural part. Such as ventures, wind tunnel test models, plastic or zinc die-casting mould cavities, surface roughness standard blocks, etc. To improve hardness, nickel-cobalt alloys can be cast, and nickel-manganese alloys can be cast to improve welding performance.

Electrophoresis is a coating method that uses an external electric field to make the particles of pigments and resins suspended in the electrophoresis liquid migrate in a directional manner and deposit on the surface of the substrate of one of the electrodes. The principle of electrophoretic coating was invented in the late 1930s, but the technology was developed and industrially applied after 1963.

Electrophoretic coating is a special coating film formation method developed in the past 30 years and is the most practical construction process for water-based coatings. It has the characteristics of water solubility, non-toxicity, and easy automation control, and has been widely used in the automotive, building materials, hardware, home appliances and other industries.

The electrophoretic coating is a coating method that puts the workpiece and the corresponding electrode into a water-soluble paint, connects to a power source, and relies on the physical and chemical effects generated by the electric field to make the resin and pigment in the paint evenly precipitate and deposit on the surface of the coated object as the electrode to form a water-insoluble paint film. Electrophoretic coating is an extremely complex electrochemical reaction process, which includes at least four processes: electrophoresis, electrodeposition, electroosmosis, and electrolysis. The electrophoretic coating can be divided into anodic electrophoresis (the workpiece is the anode and the paint is anionic) and cathodic electrophoresis (the workpiece is the cathode and the paint is cationic) according to deposition performance; it can be divided into direct current electrophoresis and alternating current electrophoresis according to power supply; and there are constant voltage and constant current methods according to process methods. At present, the anodic electrophoresis with a DC power supply constant voltage method is widely used in industry.

The difference between electroplating and electrophoresis:

The intermediate objects are different; one is metal ions, and the other is colloids. The results after treatment are also different.

Electroplating is to plate a layer of metal, which has the functions of protection, rust prevention, and beauty; electrophoresis is generally used for spray painting, that is, a layer of paint is applied on the surface, which is often used in the automotive industry.

Electroplating has a metallic texture. Electrophoresis is just a high imitation of electroplating, and there is still a certain gap in performance and colour. It is difficult for electrophoresis to produce the metallic texture of electroplating.

The principle of sputtering is to use glow discharge to ionize argon (Ar) and impact the target surface. The atoms of the target material are ejected and deposited on the substrate surface to form a thin film. The properties and uniformity of the sputtered film are better than those of the evaporated film, but the coating speed is much slower than that of the evaporated film. Almost all new sputtering equipment uses a strong magnet to make the electrons move in a spiral shape to accelerate the ionization of the argon gas around the target material, increasing the probability of collision between the target and the argon ions, thereby increasing the sputtering rate. Generally, most metal coatings use DC sputtering, while non-conductive ceramic materials use RF AC sputtering. The basic principle is to use glow discharge (glow-discharge) in a vacuum to impact the argon (Ar) ions on the target surface. The cations in the plasma will accelerate to the negative electrode surface of the sputtered material. This impact will cause the target material to fly out and deposit on the substrate to form a thin film.

Several characteristics of thin film coating by sputtering process:

(1) Metals, alloys, or insulators can be made into thin film materials.

(2) Under appropriate setting conditions, multi-component complex target materials can be made into thin films of the same composition.

(3) By adding oxygen or other active gases to the discharge atmosphere, a mixture or compound of target material and gas molecules can be made.

(4) The input current of the target material and the sputtering time can be controlled, and it is easy to obtain high-precision film thickness.

(5) Compared with other processes, it is more conducive to the production of large-area uniform thin films.

(6) The sputtering particles are almost unaffected by gravity, and the positions of the target material and the substrate can be freely arranged.

(7) The adhesion strength between the substrate and the film is more than 10 times that of the general vapour deposition film, and because the sputtering particles carry high energy, they will continue to diffuse on the film-forming surface to obtain a hard and dense thin film. At the same time, this high energy allows the substrate to obtain a crystalline film at a relatively low temperature.

(8) The nucleation density is high at the initial stage of film formation, and extremely thin continuous films below 10nm can be produced.

(9) The target material has a long lifespan and can be produced automatically and continuously for a long time.

(10) The target material can be made into various shapes, and the special design of the machine can be used for better control and the most efficient production.

The difference between evaporation and sputtering:

Sputtering is the abbreviation of vacuum sputtering coating, which is a physical coating method.
Vacuum coating mainly refers to a type of coating that needs to be carried out under a high vacuum degree, including many types, including vacuum ion evaporation, magnetron sputtering, MBE molecular beam epitaxy, PLD laser sputtering deposition, and many other types. The main idea is to divide it into evaporation and sputtering.

The substrate to be coated is called the substrate, and the material to be coated is called the target. The substrate and the target are in the same vacuum chamber.

Evaporation coating generally heats the target material to evaporate the surface components in the form of atomic groups or ions, settle on the surface of the substrate, and form a thin film through the film-forming process (scattered points-island structure-vagal structure-layered growth).

The sputtering coating can be simply understood as bombarding the target material with electrons or high-energy lasers, sputtering the surface components in the form of atomic groups or ions, and finally depositing them on the surface of the substrate, undergoing a film-forming process, and finally forming a thin film.

An electrolytic process in which the metal sheet providing the plating metal acts as the anode, the electrolyte is usually an ionic solution of the metal being plated, and the object being plated acts as the cathode. When a voltage is input between the anode and the cathode, the metal ions in the electrolyte are attracted to the cathode and are reduced and then plated on it. At the same time, the metal in the anode dissolves again, providing the electrolyte with more metal ions. In some cases, an insoluble anode is used, and a new electrolyte needs to be added during electroplating to replenish the plated metal ions.

Generally, aluminum alloys are easily oxidized. Although the oxide layer has a certain passivation effect, it will still peel off and lose its protective effect after long-term exposure. Therefore, the purpose of anodizing is to use its easy oxidation characteristics to control the formation of the oxide layer by electrochemical methods to prevent further oxidation of the aluminum material and increase the mechanical properties of the surface.