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PCBA Clean

PCBA Clean

In the process of PCB assembly processing, we need auxiliary agents to help soldering. As a matter of fact, after oxidation or high temperature, will generate som pollutants or spots on the PCBA surface. These residues not only affect the appearance, but also affect the quality of PCBA.

Therefore, many PCBAs need to be cleaned before they can be regarded as a new product.To the purpose of cleaning, the surface we use wetting, dissolved, brush, saponify and etc.  To remove the residue from the surface of the assembly board by applying different ways of mechanical force.

1、 Surface wetting
The decontamination medium forms a uniform thin layer on the surface of the washed object to wet the surface of the washed object and swell the pollutants on the surface of the washed object. The condition of surface wetting is that the surface tension of the washing medium is required to be less than that of the washed object. Adding some surfactants to the cleaning medium can significantly improve the wetting ability.

2、 Dissolve
The main decontamination mechanism of organic solvent cleaning is dissolution. The principle of similarity and compatibility shall follow when selecting solvents. Polar solvents shall be selected for polar pollutants and nonpolar solvents shall be selected for nonpolar pollutants. However, polar solvents and nonpolar solvents are often mixed in practical production. Adding some surfactants in organic solvent cleaning can improve the dissolving ability of detergent to line retention.
(1) Ionic dissolution
Ionic dissolution, that is to say, to the dissociation of pollutants into ions in water.
The dissolution of this ionic substance will improve the conductivity of water. The negative ionic pollutants on the surface assembly board include the active substances in the flux. The reactants between the active substances in the flux and metal oxides, the salt in hand sweat, the polymer in the manufacture of printed circuit board and the salt in the residue after welding, etc.  For these reasons,  can be no doubt lead to poor electrical performance of electronic products or solder joint corrosion.
(2) Nonionic dissolution
Nonionic dissolution means that pollutants dissolve in water without changing the conductivity of water.
Typical non-ionic pollutants are flux bodies, such as polyethylene, dirt in hands, phase substances in water and similar compounds. These substances are not conductive, but will absorb moisture, reduce insulation resistance and corrode SMT processing solder joints.

3、 Emulsification
In the water cleaning and semi water cleaning processes, a certain amount of emulsifier can be added to the water. When cleaning synthetic resin pollutants, these pollutants are emulsified with emulsifier and dissolved in water. The addition of surfactant can improve the emulsification.

4、 Saponification
Saponification is not only a simple chemical process, but also a neutralization reaction
The saponification reaction uses fat acid proof salt, which makes rosin and dioic acid saponify. So that to dissolve in water and remove the residue on the surface of the PCBA. Saponifier will corrode metal surfaces such as aluminum and aluminum. Therefore, when using saponifier, the compatibility between saponifier and components and other materials shall be.

5、Other clean ways
(1) Brush.
There are two ways in brush PCBA,  manual brushing and mechanical brushing. Manual cleaning , that is to say to manual cleaning of PCBA after soldering by operators holding brushing tools. Mechanical brushing refers to brushing by brushing tools installed on cleaning equipment.

(2) Spray wash in air.
In the closed container, spray washing is carried out by increasing water pressure and flow. Spray cleaning has two methods: batch cleaning and on-line cleaning. The energy (pressure and flow) of water flow directly affects the cleaning effect. Under the same water flow, high pressure is more conducive to the cleaning of residues. However, if the pressure is too high, that will affect the clean effect. For this reason,  of the large back splash when the water hits the surface of the assembly board. Low pressure water flow can play a soaking effect, which is conducive to the dissolution of residues. Therefore, the spray washing method combining high and low pressure flow is generally adopted.
(3) Immersion spray cleaning (jet cleaning).
It refers to liquid flow flushing immersed under the liquid level. To install the nozzle below the liquid level and discharged at the relative positions on both sides of the washing machine. So as to ensure that the liquid flows do not look for each other. To form a hot bath effect. This method is suitable for products that are sensitive to acoustic waves and suitable for flammable, explosive, volatile and foaming agents.
(4) Centrifugal washing.
The principle is that the torque formed by motor power makes PCBA produce centrifugal force. The dirt will separate from the surface of PCBA by centrifugal force. This cleaning method can make the cleaning liquid and washing liquid penetrate the parts that are difficult to clean, such as narrow spacing, small gaps, holes and holes, so as to achieve the purpose of cleaning. Centrifugal cleaning is suitable for post welding cleaning of high-density PCBA.
(5) Ultrasonic cleaning.
Last but not least, ultrasonic cleaning relies on cavitation and acceleration to promote physical and chemical reactions. This cavitation effect of ultrasonic can penetrate into the small areas that are difficult to reach by other cleaning methods, and the cleaning efficiency is relatively high.

However, some components on PCBA cannot be cleaned due to their particularity. In brief, we will pay more attention to the minimum flux residue when welding.

In general, whether to clean PCBA after welding and which cleaning method to choose, our primary consideration is the quality of the PCBA board.


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