Cleaning technology of circuit boards in PCB copy boards

At present, there are four main new generation cleaning technologies for circuit boards:

1.Semi-aqueous cleaning technology

Semi-aqueous cleaning mainly uses organic solvents and deionized water, plus a certain amount of surfactants and additives to form a cleaning agent. 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 points and relatively low toxicity. They are 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 rinsing easier. The characteristics of the semi-aqueous cleaning process are:

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

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

3) Drying is required after rinsing.

The disadvantage of this technology is that waste liquid and wastewater treatment is a relatively complex issue that has yet to be completely resolved.

2.Water cleaning technology

Water cleaning technology is the future development direction of cleaning technology. It is necessary to set up a pure water source and a 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. It can remove water solvents and non-polar pollutants. Its cleaning process characteristics 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, and both polar and non-polar pollutants can be easily cleaned, with a wide cleaning range;

3) Multiple cleaning mechanisms. Water is a very polar solvent. In addition to dissolving, it also has saponification, ^^^ization, displacement, dispersion and other joint effects. Using ultrasound is much more effective than in organic solvents;

4) As a natural solvent, it is relatively cheap and widely available.
The disadvantages of water cleaning are:

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

2) Some components cannot be cleaned with water, and metal parts are prone to rust;

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

4) Drying is difficult, and energy consumption is high;

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

3.No-cleaning technology

In the welding process, no-cleaning flux or no-cleaning solder paste is used, and the next process is directly entered after welding without cleaning. No-cleaning technology is currently the most used replacement technology, especially mobile communication products basically use no-cleaning methods to replace ODS. At present, many kinds of no-cleaning fluxes have been developed at home and abroad, such as Beijing Jingying Company’s no-cleaning flux. No-cleaning fluxes can be roughly divided into three categories:

1) Rosin type flux: Reflow soldering uses inert rosin solder (RMA), which can be no-cleaned.
2) Water-soluble flux: clean with water after welding.

3) Low solid content flux: no cleaning.

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

4.Solvent cleaning technology

Solvent cleaning mainly uses the dissolving power of the solvent to remove pollutants. Solvent cleaning requires simple equipment because of its fast evaporation and strong dissolving ability. According to the selected cleaning agent, it can be divided into flammable cleaning agents and non-flammable cleaning agents.

The former mainly includes organic hydrocarbons and alcohols (such as organic hydrocarbons, alcohols, glycol esters, etc.), and the latter mainly includes chlorinated hydrocarbons and fluorinated hydrocarbons (such as HCFCs and HFCs). HCFC cleaning agent and its cleaning process characteristics

This is a hydrogen-containing chlorofluorocarbon with low latent heat of evaporation, good volatility, easy decomposition in the atmosphere, and relatively small effect on the ozone layer.

It is a transitional product and is scheduled to be phased out before 2040. Therefore, we do not recommend the use of this type of cleaning agent.

There are two main problems: one is transitional.

Because it still has a destructive effect on the ozone layer, it is only allowed to be used until 2040; the other is that the price is relatively high and the cleaning ability is weak, which increases the cleaning cost.

Cleansing process characteristics of chlorinated hydrocarbons
Chlorinated hydrocarbons such as dichloromethane and trichloroethane are also non-ODS cleaning agents.

Its cleaning process features are:

1) It has a particularly strong ability to clean grease and oil dirt;
2) Like ODS cleaning agents, it can also be washed with steam and dried in the gas phase;
3) The cleaning agent does not burn or explode, and is safe to use;
4) The cleaning agent can be distilled and recovered, and can be used repeatedly, which is relatively economical;
5) The cleaning process is also the same as that of ODS cleaning agents.

However, its disadvantages are that chlorinated hydrocarbons are relatively toxic, and workplace safety issues need special attention; second, chlorinated hydrocarbons have poor compatibility with general plastics and rubbers; third, chlorinated hydrocarbons have poor stability, and must be added with a stabilizer when used.

Characteristics of hydrocarbon cleaning process

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

1) It has strong cleaning ability for grease and oil, strong and durable cleaning ability, low surface tension, and good cleaning effect for fine cracks and pores;

2) It does not corrode metals;

3) It can be distilled and recycled, and reused repeatedly, which is relatively economical;

4) It has low toxicity and less environmental pollution;

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

The main disadvantage of hydrocarbon cleaning process is safety, and strict safety measures must be taken.

Characteristics of alcohol cleaning process

Among alcohols, ethanol and isopropanol are commonly used organic polar solvents in the industry. Methanol is more toxic and is generally only used as an additive. The characteristics of alcohol cleaning process are:
1) It has good solubility for ionic pollutants, and is very effective in cleaning rosin flux, but has weak solubility for grease;
2) It has good compatibility with metal materials and plastics, and does not cause corrosion and volume expansion;
3) It dries quickly, and is easy to dry or air dry, without the 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 agents is high volatility, low flash point, and easy combustion. Explosion-proof measures must be taken for cleaning equipment and auxiliary equipment.