Etching is to process the surface of the object by chemical strong acid corrosion, mechanical polishing, or electrochemical electrolysis. In addition to increasing the aesthetics, it can also increase the added value of the product. From traditional metal processing to high-tech semiconductor manufacturing are all applications of etching technology.
What is an etching process?
Metal etching is a technique in which metal materials are removed by chemical reaction or physical impact. Metal etching technology can be divided into wet etching and dry etching. Metal etching is composed of a series of chemical processes. Different etchants have different corrosion properties and strengths for different metal materials.
Metal etching is also called photochemical etching, which refers to the removal of the protective film of the metal etching area after exposure, plate making and development, and contact with chemical solutions during metal etching to achieve the effect of dissolving corrosion, forming bumps, or hollowing out. It was first used in the manufacture of copper plate, zinc plate, and other printing concave and convex plates, and widely used to reduce the weight of instrument panels, or the processing of thin workpieces such as nameplates. After continuous improvement of technology and process equipment, etching technology is now used in the aviation, machinery, chemical industry, and semiconductor manufacturing processes, the processing of precision metal etching products for electronic thin parts is carried out.
Types of etching technology
Etching process flow:
- Wet etching:
Wet etching is to immerse the wafer in a suitable chemical solution, or spray the chemical solution quenching onto the wafer, and remove the atoms on the surface of the film through the chemical reaction between the solution and the etched object to achieve the purpose of etching.
When wet etching is performed, the reactants in the solution first diffuse through the stagnant boundary layer before reaching the surface of the wafer, and a chemical reaction occurs and various products are produced. The products of the chemical reaction of etching are products in the liquid or gas phase, and these products then diffuse through the boundary layer and dissolve into the main solution. Wet etching will not only etch in the vertical direction but also have a horizontal etching effect. Lateral etching will cause the phenomenon of undercut so that the pattern cannot be accurately transferred to the wafer.
- Dry Etching:
Dry etching is usually a kind of Plasma Etching. Due to the different etching effects, the Physical Bom of the ions in the plasma, the Chemical Reaction of the Active Radical, and the surface atoms of the device (wafer), or the combination of the two, include the following:
Dry etching is an Anisotropic Etching with good Directional Properties but poorer Selectivity than wet etching. In plasma etching, plasma is a partially dissociated gas, and gas molecules are dissociated into electrons, ions, and other species with high chemical activity. The biggest advantage of dry etching is "anisotropic etching". However, the selectivity of (radical) dry etching is lower than that of wet etching. This is because the etching mechanism of dry etching is a physical interaction; therefore, the impact of ions can not only remove the etched film but also the photoresist mask will be removed.
- Physical etching: Sputter Etching, Ion Beam Etching
- Chemical etching: Plasma Etching
- Physical and chemical composite etching: Reactive Ion Etching (RIE)
Depending on the type of metal, the etching process will vary, but the general process is as follows: metal etching plate → cleaning and degreasing → water washing → drying → film or screen printing ink → drying → exposure graphics → development → water washing drying→etching→unfilming→drying→inspection→package of the finished product.
Matters needing attention in an etching process
- Cleaning process before metal etching
The processes before the etching of stainless steel or other metals are cleaning treatments, and the main function is to remove dirt, dust, oil stains, etc. on the surface of the material. The cleaning process is the key to ensure that the subsequent film or screen-printing ink has good adhesion to the metal surface. Therefore, it is necessary to completely remove the oil and oxide film on the metal etched surface. Degreasing should be based on the oil contamination of the workpiece. It is best to electro-degrease before the screen-printing ink to ensure the degreasing effect. In addition to the oxide film, the best etching solution should be selected according to the type of metal and film thickness to ensure that the surface is cleaned. It must be dried before screen printing. If there is moisture, it will also affect the adhesion of the ink and affect the effect of subsequent pattern etching.
- Paste dry film or silkscreen ink photosensitive adhesive layer
According to the actual product material, thickness, and the precise width of the graphics, confirm the use of dry film or wet film screen printing. For different thickness products, when applying the photosensitive layer, the etching processing time and other factors required for the product graphics should be taken into consideration. A thicker or thinner photosensitive adhesive layer can be made, so that the covering performance is good, and the pattern produced by metal etching has a high definition.
After the film or roll-on screen-printing ink is completed, the photosensitive adhesive layer needs to be thoroughly dried to prepare for the exposure process. At the same time, it is necessary to ensure that the surface is clean, free of adhesion, impurities, etc.
This process is an important process of metal etching, and the exposure energy will be considered according to the thickness and precision of the material of the product. This is also a manifestation of the technical capabilities of an etching processing company. The exposure process determines whether the etching can ensure better dimensional control accuracy and other requirements.
After the photosensitive adhesive layer on the surface of the metal etching plate is exposed to light, the pattern adhesive layer is cured after exposure to light. After that, the parts that are not needed in the pattern, that is, the parts that need to be corroded, are exposed. The development process also determines whether the final size of the product can meet the requirements. This process will completely remove the unnecessary photosensitive adhesive layer on the product.
- Etching or etching process
After the product pre-manufacturing process is completed, the chemical solution will be etched. This process determines whether the final product is qualified. This process involves the concentration, temperature, pressure, speed, and other parameters of the etching solution. The quality of the product needs to be jointly determined by these parameters.
The surface of the etched product is still covered with a layer of photosensitive glue, and the photosensitive glue layer on the surface of the product after the etching process needs to be removed. Since the photosensitive adhesive layer is an acidic substance, most of them use the acid-base neutralization method for bulking. After overflow water washing and ultrasonic cleaning, the photosensitive adhesive layer on the surface is removed to prevent the residue of the photosensitive adhesive.
After the removal of the film is completed, the follow-up is testing, packaging, and the final finished product to confirm whether it meets its specifications.
- Reduce side corrosion and protruding edges, improve metal etching processing coefficient:
Generally, the longer the printed board is in the metal etching solution, the more serious the side etching. Undercutting seriously affects the accuracy of printed wires, and severe undercutting will make it impossible to make fine wires. When the undercut and the edge are reduced, the etching coefficient increases. A high etching coefficient indicates the ability to maintain thin wires and make the etched wires close to the size of the original image. Whether the electroplating etching resists is tin-lead alloy, tin, tin-nickel alloy, or nickel, etc., excessive protruding edges will cause short circuits in the wires. Because the protruding edge is easily broken, an electrical bridge is formed between the two points of the wire.
- Improve the consistency of the etching processing rate between the board and the board:
In continuous board etching, the more consistent the metal etching processing rate, the more uniformly etched boards can be obtained. To always maintain the best etching state during the pre-etching process, it is necessary to choose an etching solution that is easy to regenerate and compensate, and the etching rate is easy to control. Select technology and equipment that can provide constant operating conditions and can automatically control various solution parameters. It can be achieved by controlling the amount of dissolved copper, PH value, solution concentration, temperature, uniformity of solution flow, etc.
- Improve the uniformity of the metal etching processing rate of the entire board surface:
The etching uniformity of the upper and lower sides of the board and each part on the board surface is determined by the uniformity of the metal etchant flow rate on the surface of the board. During the etching process, the etching rates of the upper and lower plates are often inconsistent. The etching rate of the lower plate surface is higher than that of the upper plate surface. Because of the accumulation of solution on the upper plate surface, the etching reaction is weakened. The uneven etching of the upper and lower plates can be solved by adjusting the spray pressure of the upper and lower nozzles. Adopting a spray system and swinging the nozzle can further improve the uniformity of the entire surface of the board by making the spray pressure at the center and the edge of the board different, and intermittently etching the metal at the front and back of the board.
Advantages of the etching process:
Because the metal etching process is etched through chemical solutions.
- Maintain a high degree of consistency with the raw materials: do not change the properties of the material, the stress of the material, and the hardness, tensile strength, yield strength, and ductility of the material. The base processing process is etched in the atomized state in the equipment, and there is no obvious pressure on the surface.
- No burrs: During the product processing, there is no pressing force during the whole process, so there will be no curling, bumps, and pressure points.
- It can cooperate with the post-process stamping to complete the individual forming action of the product, and can carry out the full-page electroplating, adhesive, electrophoresis, blackening, etc. in the way of hanging points, which is more cost-effective.
- Miniaturization and diversification can also be dealt with, and the cycle is short and the cost is low.