In the previous article, we conducted a comprehensive analysis of the sources, classifications, and hazards of pollutants generated in electronic processes. This article will introduce the evolution and development trends of cleaning technologies involved in electronic processes, and classify the currently used cleaning technologies. By comparing the advantages and disadvantages of different types of electronic cleaning technology, the development trend of electronic cleaning technology is clear, and the development of safe and environmentally friendly water-based cleaning agent is the development trend of electronic cleaning.

With the rapid development of the electronics industry, electronic products continue to develop in the direction of miniaturization, high density, integration, and high reliability. In the process of electronic manufacturing, more and more pollutants are inevitably introduced. The problem of electron failure caused by the presence of contaminant residues has also become more and more. In order to ensure the smooth progress of the electronic manufacturing process and ensure the quality and reliability of the product, the cleaning process must be introduced in the process of process implementation. The cleaning process and technology are probably developed in the following stages.

Solvent cleaning technology

Early cleaning agents used in electronic cleaning processes are mainly solvent-based cleaning agents for fluorine-containing Lyon (CFC-1 13), 1,1,1-trichloroethane, carbon tetrachloride and the like. The cleaning agent has the advantages of good chemical stability, no flash point, no burning, no explosion, fast drying and strong dissolving power, and has wide applicability. However, the ODS type cleaning agent has a strong destructive power to the ozone layer, and the ODS has a strong GWP (greenhouse effect potential value), which seriously endangers the human ecological environment. Therefore, the Montreal Protocol, enacted in 1987, stipulates that developed countries will no longer use ODS substances from 1996, while developing countries are allowed to postpone this regulation for 10 years. Since 2010, China has also stopped the production and use of major ODS (Ozone Depleting Substances), two major categories of chlorofluorocarbons (CFCs) and halons. Therefore, the development of alternative technologies for HCFC cleaning is an urgent problem to be solved in the current development of the electronics industry.

For cleaning of traditional electronic processes, more cleaning agents are still solvent-based cleaning agents. Most of these cleaning agents have good cleaning effects, but they have the disadvantages of high toxicity, greenhouse effect, ozone depletion, low flash point, flammability and explosiveness. For example, HCFC-based solvents have strong dissolving power and good cleaning effect, but they are ODS-based non-environmental substances, and will be phased out by 2020. Halogenated hydrocarbon solvents are highly toxic to humans and have carcinogenic effects. Many companies have banned their use. Hybrid solvent cleaners such as petroleum, alcohols, ethers and esters are relatively environmentally friendly and can be used as a substitute for ODS solvents in some cleaning applications. However, the cleaning agent prepared by such a solvent has a weak cleaning power and cannot achieve a cleaning effect similar to HCFC, and the cleaning agent has a low flash point, is flammable and explosive, and has a large safety hazard.

In order to better protect employees’ health and protect the earth’s ecological environment, the electronic cleaning industry is gradually abandoning toxic and harmful VOC solvents and switching to semi-aqueous, water-based, VOC-free or low-VOC cleaning agents.

2. Semi-aqueous cleaning technology

The semi-aqueous cleaning agent is a new cleaning agent developed in the practice of the cleaning process in order to maintain the advantages of solvent cleaning while overcoming its shortcomings. Usually it is formed by adding a small amount of water and a surfactant to an organic solvent. In its composition, the organic solvent is still the main body, so it basically maintains the original properties of the organic solvent. The semi-aqueous cleaning agent has high dissolving power and high cleaning cleanliness. The organic solvent contains good cleaning ability for organic substances, and the surfactant provides wetting, emulsifying and rinsing functions. The rinsing process has the characteristics of removing ionic components and water-soluble contaminants, and reduces the volatility and flammability of the original flammable solvent, and is compatible with most metal and plastic materials.

Although semi-aqueous cleaners have many advantages, they still encounter many problems when used. The use of a semi-aqueous cleaning agent is more complicated than a solvent cleaning agent, and an rinsing and drying process is required. The moisture contained in the cleaning agent and the rinsing liquid may also cause rust corrosion of the metal material, and the waste liquid after cleaning may not be recycled, and the treatment is difficult, the treatment amount is large, and the use cost is high. At the same time, the cleaning agent still contains a large amount of organic solvent, and it is still necessary to consider the protection of toxic solvents and the problem of fireproofing and explosion prevention. These shortcomings severely limit the application of semi-water-based technology, making the semi-aqueous cleaning agent not widely used.

3. Water-based cleaning technology

The Montreal Protocol, which was enacted in 1987, has led to the rapid development of water-based cleaners and even the cutting edge of CFC materials. After decades of development, water-based cleaning agents have become more mature technologies and are widely used as cleaning agents in recent years. The main components are surfactants, emulsifiers, penetrants, etc., and the cleaning of pollutants is achieved by the functions of wetting, emulsifying, penetrating, dispersing, and compatibilizing. The cleaning agent has good compatibility, low price, safe operation, non-combustible and non-explosive, high degree of freedom in cleaning and formulation, and can be adjusted for different nature pollutants, and then combined with physical cleaning such as heating, brushing, spraying, ultrasonic cleaning, etc. Means, good cleaning effect on both polar and non-polar pollutants.

Water-based cleaners are generally classified into neutral water-based cleaners and alkaline water-based cleaners. Due to the lack of cleaning power of neutral water-based cleaning agents, alkaline water-based cleaning agents are still the main market. Material compatibility should be considered when using alkaline products. Moreover, heating and ultrasonic cleaning and spray cleaning are generally required during cleaning. Drying equipment is used when drying, and power consumption is large, and wastewater treatment needs to be considered uniformly. Water-based cleaning agents have the advantages of safety and environmental protection, wide cleaning range, good compatibility with most of the materials to be cleaned, and low comprehensive cost. At the same time, many companies prefer water-based cleaning agents based on relevant laws and policies. This requires water-based cleaners to improve cleaning performance, improve drying performance, recyclability and environmental friendliness to meet the growing needs of the electronics industry.

4. No-clean technology

Due to the emergence of the no-clean flux \ solder paste in the early 1990s, the word “free wash” became the hottest topic at the time. According to current standards, no-clean means that the residue of the board is safe from a chemical point of view and does not have any effect on the board. By testing corrosion, SIR, electromigration and other testing methods, the safety and reliability of the disposable components can be determined. Switching to the no-clean process saves on cleaning equipment, cleaning agents, etc., but the use of a low solids no-clean flux or solder paste will leave more or less residue. “No-clean” violates the trend of electronic products to finer pitch, higher reliability, higher density packaging and low cost. For enterprises with higher degree of automation, larger production scale, and less demanding reliability index of post-weld products, no-cleaning process can be adopted, and for products with high reliability requirements, any pollutants or residues will be applied to electronic products. The safety reliability has an impact, so no-cleaning does not mean that cleaning is not required, and the cleaning process plays an increasingly important role in the electronic process.

5. Conclusion

As the electronics industry demands higher and higher reliability and safety, its requirements for cleaning processes have increased. Cleaning, as a process in the manufacture of electronic products, has shown an increasingly important role. At present, China’s electronics industry has not yet formed a uniform quality cleaning specification for PCB circuit board cleaning as a final product. IPC-CN-65B CN “Printing Board and Component Cleaning Guide” translated by IPC and IPC TG Asia 5-31CN technical group. Provides an authoritative basis for cleaning evaluation of electronic process cleaning.

Today, with the increasing concern of environmental protection and safety in manufacturing companies around the world, traditional high-pollution, highly toxic and flammable and explosive chemical solvent cleaners will surely withdraw from the historical arena. Water-based cleaning agents based on natural environmentally friendly materials are the best choice for electronic process cleaning due to their low toxicity, environmental protection, low toxicity to humans, non-flammable and explosive, degradable and long service life.