Whenever electronic products are soldered, flux or other types of contaminants always remain on the surface of the PCB (printed circuit board), even if halogen-free cleaning flux is not used. In my experience, never trust "dirty" too much. In short, PCB cleaning after surface mount soldering plays a vital role in ensuring the reliability, electrical function and service life of electronic products. This article will discuss the importance of cleaning after surface mount soldering and list some common cleaning methods.

1.Source analysis of pollutants

After surface mount soldering, the white contaminants left on the surface of the PCB board contain complex components. They can be fluxes, oxides or fluxes and metal reagents, solder masks and PCB laminates. In addition to the above substances, the generation of white pollutants is related to other elements, including PCB design, SMT technology (such as reflow time and temperature), temperature and humidity.

2. PCB clean up method after surface mount soldering

1)Manual cleaning method

The acetone solution is used to soak the PCB board for about 10 minutes. Then, use a railing brush to remove contaminants from the solder joints in the ethanol solution. Next, the plate was removed before washing with deionized water for 3 minutes. After that, dehydration was carried out using absolute ethanol. Finally, use a nitrogen gun to dry the surface of the circuit board until no water marks can be seen. In the manual cleaning process, the circuit board is soaked with acetone, which has high solubility, which can effectively dissolve the contaminants in the solution. The circuit board is then physically brushed by placing the circuit board in ethanol to remove fine solder contaminants. Next, the organic solvent must be dehydrated with the help of deionized water. Finally, the circuit board surface is dried with nitrogen to complete manual cleaning after surface mount soldering.

2)Ultrasonic cleaning method

Acetone solvent is used for ultrasonic cleaning method. First, immerse the PCB in acetone solvent for 10 minutes. Then, it was placed in a quartz container dedicated to absolute ethanol, in which the circuit board was impregnated. Next, after placing the quartz container in the ultrasonic cleaning tank, ultrasonic cleaning is performed. The ultrasonic cleaning lasts 5 minutes, the ultrasonic power is 240W, and then the quartz container is taken out with a basket after the ultrasonic cleaning switch is turned off. Then, it was washed with deionized water for 5 minutes and dehydrated with absolute ethanol on the circuit board. Finally, nitrogen is used to dry the surface. In the ultrasonic cleaning process, the circuit board is placed in ethanol, which is different from manual cleaning. According to the principle of ultrasonic vibration, ultrasonic cleaning aims to remove flux residues and dehydrate it with deionized water. Finally, it enters the drying stage with the help of nitrogen.

3) Gas phase cleaning method

First turn on the equipment condensation system and let it run for 5 to 10 minutes. Then, turn on the equipment heating system and heat the cleaning agent to boiling temperature. Place the circuit board in the cleaning basket, and then place it in the boiling tank. The boiling time is 3 to 5 minutes. Then, place the basket in the steam zone for steam cleaning for 3 to 5 minutes. Then, spray the surface of the circuit board with the cleaning agent for 10 to 20 seconds. After that, place the basket slightly in the rinse tank for 1 to 2 minutes. Finally, the device is dried by condensation, and the basket is taken out after the agent has completely evaporated. When the PCB board is placed in the steam of hot agent, the hot steam will condense on the surface. The circuit board with a relatively cold surface dissolves the grease and dirt on the surface of the PCB component. The dissolved grease dirt is immersed in the boiling agent, while the steam accumulates on the condensation coil around the boiling agent. The steam will return to the separation chamber in liquid form, which can be recycled with filtration of the separated water and impurities.

3. Comparison between all clean up methods

By observing the PCB routing and surface conditions, and comparing the manual cleaning, ultrasonic cleaning and gas phase cleaning methods on the PCB after surface mount soldering, it can be concluded that the flux residue can be thoroughly cleaned and the PCB surface is cleaned thoroughly by organic solvents. However, manual cleaning and ultrasonic cleaning sometimes still leave flux residues on certain parts of the PCB. Therefore, the comprehensive analysis concluded that organic solvent cleaning equipment should have higher reliability, lower toxicity and higher safety, so that the cleaning becomes thorough and produces a better cleaning effect.

4. Importance of clean up after surface mount soldering

1)PCB cleaning after surface mount soldering can prevent the occurrence of electrical defects.

Among all the electrical defects, leakage is the most prominent, which is the basic element that reduces the long-term reliability of the PCB board. Such defects are mainly caused by ionic contaminants, organic residues and other adherent substances remaining on the surface of the circuit board.

2) PCB cleaning after surface mount soldering can eliminate corrosive substances. Corrosion can damage circuits and the main components or devices are brittle. Corrosive substances can conduct electricity in a humid environment, which will further cause short circuit or even failure of the PCB board. Eliminating corrosive substances actually excludes the negative elements that hinder the long-term reliability of the PCB.

3) PCB cleaning after surface mount soldering can make the circuit board look clear.

The PCB board cleaned after surface mount soldering has a clear appearance and exposes some defects, which is convenient for inspection and troubleshooting, such as thermal damage and lamination.

In short, electronic assembly capabilities are not limited to manufacturing and assembly technology. However, in terms of board soldering and soldering PCBs, flux electronic devices are also inevitable, and they play a vital role in determining the reliability and functionality of the final electronic product.