PCBA Tech - PCBA processing cleaning method and process flow

PCBA processing cleaning method and process flow
The cleaning methods of printed circuit components are mostly classified according to the nature of the solution medium used during cleaning, and are mainly divided into three categories: solvent cleaning method, semi-aqueous cleaning method and water cleaning method.

1. Solvent cleaning method
(1) Batch solvent cleaning process. The batch cleaning process is also called intermittent cleaning. The main process flow is: the printed circuit components to be cleaned are placed in the vapor zone of the cleaning machine. Because there are condensers around the vapor zone, when the solvent located in the lower part of the vapor zone is When heated, it becomes a vapor state and when it rises to the surface of the cooled component, it is condensed into a solvent, and interacts with the contaminants on the component surface and then drops with the droplets to take away the contaminants. After the cleaned component stays in the vapor zone for 5-10 minutes, the clean liquid recovered by the condensation of the solvent vapor is sprayed on the component to flush out contaminants. When the surface temperature of the components staying in the vapor zone reaches the vapor temperature, the surface no longer produces condensate. At this time, the components are clean and dry and can be taken out. The cleanliness of the components cleaned by this cleaning method is high, and it is suitable for small batch production, and occasions where the pollution of printed circuit components is not serious and the cleanliness requirements are high. Its operation is semi-automatic, and a small amount of solvent vapor will leak, which has an impact on the environment.

The main points of the batch solvent cleaning process include the following aspects.

1. Sufficient solvent should be contained in the boiling tank to promote uniform and rapid evaporation, and care should be taken to remove the residue after cleaning from the boiling tank.

2. A cleaning workbench is set in the boiling tank to support the cleaning load; the contaminated solvent must always be kept at a safe height under the workbench level frame, so that the basket containing the cleaning load will not be contaminated when it rises and falls. Take it into another solvent tank.

3. The solvent tank should be filled with solvent so that the solvent can always flow into the boiling tank.

4. After the equipment is started, there should be sufficient time to form a saturated vapor zone, and check to make sure that the condensing coil reaches the cooling temperature specified in the operation manual, and then start the cleaning operation.

5. According to the amount of use, periodically replace the solvent in the boiling tank with fresh solvent.

(2) Continuous solvent cleaning process. The continuous cleaning process is suitable for mass production and assembly line production. The cleaning quality is relatively stable. Since the operation is fully automatic, it is not affected by human factors. In addition, in the continuous cleaning process, mechanical decontamination methods such as high-pressure oblique spraying and fan-shaped spraying can be added, which is especially suitable for cleaning surface mounted circuit boards.

1. Characteristics of continuous solvent cleaning technology. The continuous cleaning machine generally consists of a long steam chamber, which is divided into several small steam chambers to adapt to the solvent cascade, solvent boiling, spraying and solvent storage, and sometimes the components are immersed in the boiling solvent . Usually, the components are placed on a continuous conveyor belt and run at different speeds depending on the type of SMA, passing horizontally through the vapor chamber. The solvent distillation and condensation cycle are both carried out in the machine. The cleaning procedure and cleaning principle are similar to batch cleaning, except that it is clear that the procedure is carried out in a continuous structure.

The key to using continuous technology to clean SMA is to choose a satisfactory solvent and the best cleaning cycle.

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2. Type of continuous solvent cleaning system. Continuous cleaning machines can be divided into the following three types according to the cleaning cycle.

a. Steam-spray-steam cycle. This is the most commonly used cleaning cycle in continuous solvent cleaning machines. The components first enter the steam zone, then into the spray zone, and finally sent out through the steam zone. In the spray area, spray up and down from the bottom and the top. This type of cleaning machine uses a combination of flat, narrow fan and wide fan nozzles, and is supplemented by high pressure, spray angle control and other measures for spraying.

b. Spray - immersion boiling - spray cycle. Continuous solvent cleaning machines using this type of cleaning cycle are mainly used for difficult-to-clean SMAs. The components to be cleaned are sprayed obliquely first, then immersed in the boiling solvent, then sprayed obliquely, and finally the solvent is removed.

c. Spray - immersion boiling with spray - spray cycle. The cleaning machine using this type of cleaning cycle is similar to the second type of cleaning machine, except that a solvent spray is added to the boiling solvent. Some also set up nozzles in the immersed and boiled solvent to form solvent turbulence. These are to further strengthen the cleaning effect.

(3) The advantages of boiling ultrasonic cleaning. The effect is comprehensive and the cleanliness is high; the cleaning speed is fast, which improves the productivity; does not damage the surface of the components to be cleaned; reduces the chance of human contact with the solvent and improves the work safety; it can clean the parts that cannot be reached by other methods.

But at the same time, because the ultrasonic wave has a certain penetration ability, it will often penetrate the package of the device into the device and destroy the solder joints of the transistor and the integrated circuit. Therefore, many countries in the world clearly stipulate that military electronic products must not be cleaned by boiling ultrasonic waves. my country's GJB3243-military standard also stipulates that military electronic products do not allow ultrasonic cleaning of printed circuit components.