PCB Tech - About printed circuit board cleaning technology analysis

The new generation of circuit board cleaning technology mainly has the following four types:

1. Semi-aqueous cleaning technology

Semi-aqueous cleaning mainly uses organic solvents and deionized water, plus a certain amount of active agents and additives. This type of cleaning is between solvent cleaning and water cleaning. These cleaning agents are all organic solvents, which are flammable solvents with relatively high flash point, relatively low toxicity, and relatively safe to use, but they must be rinsed with water and then dried. Some cleaning agents add 5%-20% water and a small amount of surfactants, which not only reduces the flammability, but also makes the rinsing easier. The characteristics of the semi-aqueous cleaning process are:

1) The cleaning ability is relatively strong, it can remove polar and non-polar pollutants at the same time, and the cleaning ability is strong;

2) Two different types of media are used for cleaning and rinsing, and pure water is generally used for rinsing;

3) Dry after rinsing.

The shortcoming of this technology is that waste liquid and wastewater treatment is a relatively complicated problem that has yet to be completely solved.

2. Water cleaning technology

Water cleaning technology is the development direction of cleaning technology in the future, and it is necessary to set up pure water source and discharge water treatment workshop.

It uses water as the cleaning medium, and adds surfactants, additives, corrosion inhibitors, chelating agents, etc. to the water to form a series of water-based cleaning agents. Can remove water solvents and non-polar contaminants. The characteristics of the cleaning process are:

1) Good safety, no combustion, no explosion, basically non-toxic;

2) The formula composition of the cleaning agent has a large degree of freedom, which can easily clean both polar and non-polar pollutants and has a wide cleaning range;

3) Multiple cleaning mechanisms. Water is a very polar solvent. In addition to dissolving, it also has saponification, saponification, displacement, and dispersion. The use of ultrasound is much more effective than in organic solvents;

4) As a natural solvent, its price is relatively low and its sources are wide.

The disadvantages of water cleaning are:

1) In areas where water resources are scarce, because this cleaning method consumes a lot of water resources, it is limited by the local natural conditions;

2) Departmental components cannot be cleaned with water, and metal parts are easily rusted;

3) The surface tension is large, it is difficult to clean the small gaps, and it is difficult to completely remove the residual surfactant;

4) It is difficult to dry and consumes a lot of energy;

5) The cost of the equipment is high, a wastewater treatment device is required, and the equipment occupies a large area.

3. No-cleaning technology

No-clean flux or no-clean solder paste is used in the PCB soldering process. After soldering, it will go directly to the next process and no longer be cleaned. No-clean technology is currently the most used alternative technology, especially mobile communication products. No-wash method to replace ODS. At present, many kinds of no-clean fluxes have been developed at home and abroad. No-clean fluxes can be roughly divided into three categories:

1) Rosin type flux: Inert rosin solder (RMA) is used for reflow soldering, which can be free of cleaning.

2) Water-soluble flux: clean with water after welding.

3) Low solid content flux: no cleaning.

No-clean technology has the advantages of simplifying the process flow, saving manufacturing costs and reducing pollution. In the past ten years, the widespread use of no-clean soldering technology, no-clean flux and no-clean solder paste is a major feature of the electronics industry at the end of the 20th century. The ultimate way to replace CFCs is to achieve no-clean.

4. Solvent cleaning technology

Solvent cleaning mainly uses the solvent's solvency to remove contaminants. Solvent cleaning is used, because of its fast volatilization and strong dissolving ability, so the equipment requirements are simple. According to the selected cleaning agent, it can be divided into flammable cleaning agent and non-flammable cleaning agent. The former mainly includes organic hydrocarbons and alcohols (such as organic hydrocarbons, alcohols, glycol esters, etc.), and the latter mainly includes chlorine Hydrocarbons and fluorinated hydrocarbons (such as HCFC and HFC), etc.

HCFC cleaning agent and its cleaning process characteristics. This is a hydrogen-containing chlorofluorocarbon with low latent heat of evaporation and good volatility. It is easily decomposed in the atmosphere and has a relatively small effect on destroying the ozone layer. It is a transitional product. It is scheduled to be eliminated before 2040, so we do not recommend the use of this type of cleaning agent. There are two main problems in its existence: one is transitional. Because it has a destructive effect on the ozone layer, it is only promised to be used until 2040; second, the price is relatively high and the cleaning ability is weak, which increases the cleaning cost.

Characteristics of cleaning process of chlorinated hydrocarbons

Chlorinated hydrocarbons such as dichloromethane and trichloroethane are also non-ODS cleaning agents. The characteristics of the cleaning process are:

1) The ability to clean grease and dirt is particularly strong

2) Like ODS cleaning agent, it can also be washed with steam and dried in gas phase

3) The cleaning agent does not burn or explode, and is safe to use;

4) The cleaning agent can be distilled and recycled and used repeatedly, which is more economical

5) The cleaning process is also the same as the ODS cleaning agent.

However, its shortcomings are that the toxicity of chlorinated hydrocarbons is relatively high, and safety issues in the workplace should be paid special attention; the second is that the compatibility of chlorinated hydrocarbons with general plastics and rubber is poor; the third is that chlorinated hydrocarbons are not disorderly. The above is relatively poor, so be sure to add no messy agent when using it.

Hydrocarbon cleaning process characteristics

Hydrocarbons are hydrocarbons. In the past, gasoline and kerosene obtained by distilling crude oil were used as cleaning agents. With the increase of carbon number, the flash point of hydrocarbons increases, which increases safety, but the dryness is not good; the dryness is good, and it is not safe to use, so the two are very contradictory. Of course, as the cleaning agent, a cleaning agent with good fire safety and high flash point should be used as much as possible. The characteristics of the cleaning process are:

1) It has a strong cleaning ability for grease and dirt, a long-lasting cleaning ability, and a low surface tension, which has a good cleaning effect on the crevices and pores;

2) Does not corrode metals;

3) It can be distilled and recycled and used repeatedly, which is more economical

4) Low toxicity and less environmental pollution;

5) The same medium can be used for cleaning and rinsing, which is convenient to use.

The most important of the shortcomings of the hydrocarbon cleaning process is the problem of safety, which requires strict safety methods and measures.

PCB alcohol cleaning process characteristics:

Among the alcohols, ethanol and isopropanol are organic polar solvents commonly used in the industry. Methanol is more toxic and is generally only used as an additive. The characteristics of the alcohol cleaning process are:

1) It has a good dissolving power for ionic pollutants, a very good cleaning effect for rosin flux, and a weak dissolving power for grease;

2) Good compatibility with metal materials and plastics, without corrosion and swelling;

3) Fast drying, easy to dry or air drying, no need to use hot air.

4) It has good dehydration properties and is often used as a dehydrating agent.

The main problem of alcohol cleaning agent is high volatility, low flash point, easy to burn, it is necessary to take explosion-proof measures for cleaning equipment and auxiliary equipment.