The substance that engraves by eroding the characteristics of the material is called an etchant. Etchants are generally highly corrosive.
Etchants have a wide range of applications in the fields of printed circuit boards, micro-optics, and plasma etching due to their good erosive properties.
- Printed circuit board: Potassium peroxodisulfate composite/sulfuric acid system is a new type of etching system currently developed. The active component of the system is potassium monopersulfate KHSO5, which is an acid salt of monopersulfuric acid, and exists as 2KHSO5·KHSO4·K2SO4 as an integral part of the trihydrate salt. The potassium monopersulfate complex is referred to as PMPS, and it is also listed as Potassium Monopersulfate Triple Salt and OXONE. It has a very powerful and effective non-chlorine oxidation ability and has been widely used in the printed circuit board (PCB) industry. This system has the advantages of uniform and stable etching rate, fast dissolution rate, high solubility, easy analysis, and easy cleaning, so it can well meet the etching needs of high-end circuit boards.
Figure 1. Etchants are used in printed circuit boards.
- Etching nuclear pore membrane: The nuclear pore membrane is a cylindrical pore structure and can be used as a filter material with excellent performance. In recent years, nuclear pore membranes have been widely used in the fields of precision filtration, particle detection, petroleum water content determination, anti-counterfeiting technology, food preservation and so on. Polypropylene nucleoporous membrane is a new type of nucleoporous membrane, which has the advantages of chemical stability to strong alkali and strong acid, good hydrophobicity, excellent mechanical properties, low material cost and wide application. The preparation process of the nuclear pore membrane is to irradiate the plastic film with high-energy heavy ions to form particle track damage in the plastic film. The film is further subjected to oxidation treatment, chemical etching, cleaning and other processes to obtain nuclear pore membranes with different pore sizes and different pore densities. Because polypropylene is an aliphatic hydrocarbon polymer, it has good chemical stability against common strong acids and bases, so most of the etchant is ineffective for the preparation of polypropylene core pore membranes. The sulfuric acid solution of potassium dichromate is used as an etchant, which can oxidize the polypropylene polymer to produce propionic acid, and at the same time generate many small molecular oxidation products after the carbon-carbon bond is broken, such as acetic acid and carbon dioxide, so as to obtain the required nuclear pore membrane.
- Plasma etching: Plasma etching, also known as dry etching, refers to the removal of material on the surface by a plasma process. Plasma etching is mainly used for the degradation of oxide layer, the etching of semiconductor and the spraying of distillation source. The plasma etching of the process gas is to convert the etchant from the solid phase to the gas phase, and to suck out the gas phase products through the vacuum pump, so as to etch part of the area or part of the structure. The gas etchant used for plasma etching mainly includes SF6 gas etchant, CF4 gas etchant and NF3 gas etchant. Because the N-F binding energy is smaller than the S-F and C-F binding energy, the energy consumption for etching with NF3 is lower and the etching speed is faster. Therefore, compared with SF6 gas etchant and CF4 gas etchant, NF3 gas etchant is more widely used in plasma etching.
- Other fields: In addition to the above fields, etchant is also used in some other fields. For example, engraving marble has always been processed by hand chiseling, but etching marble with an etchant has the advantages of high speed, good effect, low cost, easy operation, harmless to human body, and no pollution to the environment. More importantly, the marble etched by the etchant has good fidelity, high yield and uniformity, so the etchant is also widely used in the field of marble carving.
Figure 2. Etchants are used to etch marble.
- Moon Sook Youngr. (2019), "Chirality control for predominant metallic or semiconducting single-walled carbon nanotubes prepared using a mild etchant." Chemical communications 55, 13888-13891.
- Ardianrama Alexander David. (2019), "Reshaping of triangular silver nanoplates by a non-halide etchant and its application in melamine sensing." Journal of colloid and interface science 552, 485-493.
- Wen Yang Hsu. (2018), "Suppressing the Initial Growth of Sidewall GaN by Modifying Micron-Sized Patterned Sapphire Substrate with H3PO4-Based Etchant." Micromachines 9, 622-631.