Whenever an electronic product is soldered, flux or other types of contaminants are left on the surface of the PCB, even if halogen-free cleaning fluxes are not used. Cleaning PCBs after surface mount soldering plays a critical role in ensuring the reliability, electrical functionality and longevity of electronic products. This article will discuss the importance of cleaning after surface mount soldering and list some common cleaning methods.
The following aspects can fully explain the importance of PCB cleaning after surface mount soldering.
PCB cleaning after surface mount soldering can prevent the occurrence of electrical defects.
Of all the electrical defects, leakage is the most prominent, which is the basic element that reduces the long-term reliability of the PCB board. This type of defect is mainly caused by ionic contaminants, organic residues and other adhesive substances that remain on the surface of the board.
PCB cleaning after surface mount soldering eliminates corrosive substances. Erosion can damage circuits and cause components or devices to become brittle. Corrosive substances can conduct electricity in humid environments, which can further cause PCB short circuits or even failure. Eliminating corrosive substances virtually eliminates the negative factors that hinder the long-term reliability of PCBs.
PCB cleaning after surface mount soldering gives the board a clear appearance.
A clean PCB after surface mount soldering has a clear appearance, exposing defects that are easy to inspect and troubleshoot, such as thermal damage and lamination.
Source analysis of contaminants
White contaminants left on the surface of the PCB after surface mount soldering have a complex composition. They can be flux, oxides or flux and metal reagents, solder masks and PCB lamination materials. In addition to the substances mentioned above, the generation of white contaminants is related to other elements including PCB design, SMT technology (e.g. reflow oven soldering time and temperature), temperature and humidity.
Classification of PCB cleaning methods after surface mount soldering
1. Manual Cleaning Methods
Acetone solution is used to soak the PCB for about 10 minutes. Then, a railing brush is used to remove contaminants from the solder joints in the ethanol solution. Next, the board is removed before being washed for 3 minutes using deionized water. After that, anhydrous ethanol was used for dehydration. Finally, the surface of the board was dried using a nitrogen gas gun until no water marks were visible.
During the manual cleaning process, the board was soaked using acetone, which has a high solubility, which effectively dissolves the contaminants in the solution. The board is then physically scrubbed by placing the board in ethanol and brushing away fine solder contaminants. Next, the organic solvent must be dehydrated with the help of deionized water. Finally, nitrogen is used to dry the board surface so that manual cleaning can be accomplished after surface mount soldering. The process can be summarized in the figure below.
2. Ultrasonic Cleaning Method
Acetone solvent is used for the ultrasonic cleaning method. First, the PCB is immersed in acetone solvent for 10 minutes. Then, it is placed into a quartz container dedicated to absolute ethanol in which the board is impregnated. Next, ultrasonic cleaning is performed after the quartz container is placed in an ultrasonic cleaning tank. The ultrasonic cleaning lasted for 5 minutes with an ultrasonic power of 240 W. Then, the quartz container was removed with a basket after the ultrasonic cleaning switch was turned off. Then, the board was washed with deionized water for 5 minutes and dehydrated with anhydrous ethanol on the board. Finally, the surface was dried using nitrogen.
During the ultrasonic cleaning process, the circuit board is placed in an ethanol agent, which is different from manual cleaning. Based on the principle of ultrasonic vibration, ultrasonic cleaning aims to remove solder residues and dehydrate them with deionized water. The final stage is drying with the help of nitrogen. The entire process of ultrasonic cleaning is shown in the figure below.
3. Gas phase cleaning method
Equipment condensing system is first opened, let it run for 5 to 10 minutes. Then, turn on the equipment heating system to heat the cleaning agent to boiling temperature. Place the circuit boards in the cleaning basket and place them in the boiling tank. The boiling time is 3 to 5 minutes. The basket is then placed in the steam area for steam cleaning for 3 to 5 minutes. Then, the surface of the circuit board is sprayed with a cleaning agent for 10 to 20 seconds. After that, the basket is slightly placed in a rinse tank for 1 to 2 minutes. Finally, the basket is passed through a condensation drying unit and removed after the agent has completely evaporated.
When the PCB is placed in the thermite vapor, the hot vapor condenses on the cooler surface of the board, causing the grease fouling on the surface of the PCB components to dissolve. The dissolved grease fouling is immersed into the boiling agent while the vapor builds up on the condensation coils around the boiling agent. The vapors will return in liquid form to the separation chamber which can be recirculated with separated water and impurity filtration. The principle of pharmaceutical vapor phase cleaning is shown below.
Comparison of all cleaning methods, by observing the PCB alignment and surface conditions, and comparing manual cleaning, ultrasonic cleaning and vapor phase cleaning methods on the PCB after surface mount soldering, it can be concluded that flux residues can be thoroughly cleaned from the surface of the PCB board by organic solvent cleaning. However, manual cleaning and ultrasonic cleaning sometimes still retain flux residues on some parts of the PCB. Therefore, a comprehensive analysis concludes that organic solvent cleaning equipment should have higher reliability, lower toxicity, and higher safety, thus making cleaning more thorough and producing better cleaning results.
In conclusion, electronic assembly capabilities are not limited to the range of manufacturing and assembly technologies. However, as far as board soldering and soldering PCBs are concerned, fluxing electronics is also an unavoidable aspect that plays a vital role in determining the reliability and functionality of the final electronic product.
Features of NeoDen PCB Cleaning Machine
1. Modular drawer type design, brush cleaning or roller brush cleaning are synchronous switched mode at any time according to the needs of different work, flexibility.
2. PLC control system, HMI control panel, easier operation.
3. Use high speed spiral brush can improve cleanliness and save the consumption of sticky dust paper.
4. Use high quality cleaning roller to provide the best cleaning effect and service life.
5. Patent coupling transmission structure, is more conducive to the operation of the machine and the longer component service life.
6. Roller group and support group drawer type design for easy operation and maintenance.
7. Can be used flat-bottomed support to flat contact PCB,more conducive to the cleaning effect.
8. Three color warning device to provide different warning information.
9. SMEMA compatible.
Post time: Jan-25-2024