What is the purpose of washing PCBs? What are the PCB cleaning methods?

PCB cleaning is a post-soldering process. Its purpose is to remove flux residues and other impurities created during the PCB assembly and production process, which could be responsible for the malfunction of the final product containing PCBs. It is therefore a necessary process that contract electronics manufacturers must keep in mind. Here we will list the most popular PCB cleaning methods, taking into account their advantages and disadvantages.

Washing PCBs with deionized water

For several decades, the most common method of cleaning PCBs is the use of deionized water. The main advantages are low costs and relatively high efficiency. However, in the modern electrotechnical industry, washing PCBs with deionized water has significant limitations. First of all, due to the low surface tension, deionized water will not get into hard-to-reach places located under tight gaps. Moreover, this type of washing is ineffective against non-ionic contamination and sintered flux. Considering the frequent use of lead-free pastes, this is quite a limitation.

PCB cleaning with alcohol-based cleaning agents

Alcohol-based detergents are more effective in cleaning non-ionic residues. With their help, you can quickly and easily get rid of flux residues, even when using lead-free pastes and high soldering temperatures. The limitation, however, is a significant risk of ignition, which means that the temperature of the cleaning equipment cannot exceed 70 degrees C in this case. Machines used for cleaning PCBs with alcohol-based agents must therefore meet a number of requirements, which affects their price.

Ultrasonic method and air cleaning

The innovative ultrasound method is very popular, as it allows you to remove problematic contaminants in hard-to-reach places. It is often a supplement to traditional washing with deionized water. Ultrasound cleaning allows you to reach places inaccessible to liquid detergents. However, the method requires specialized equipment and expertise, due to the greater risk of damaging the plate. The ultrasonic method is often enriched with additional cleaning with high-pressure air.

Which of the PCB cleaning methods is the most profitable?

Choosing the right method of cleaning PCBs predisposes their design, the choice of solder paste, and the temperature during soldering. These factors influence the type of contamination that may appear on the plate. Deionized water is undoubtedly the cheapest and easiest method of cleaning PCBs. However, it has significant limitations in the fight against more difficult dirt and sintering flux. The most efficient method is the ultrasonic cleaning method enriched with pressurized air. The disadvantage, however, is the high cost of the equipment, as well as the greater risk of damaging PCBs from too much energy.

In order to give the printed circuit boards a longer life, they must be properly protected against oxidation and contamination adhering to the soldered surface.
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