Solutions of White Spots in PCBA Processing

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What is the white spot problem often mentioned in PCBA processing?

It is common for certain PCBA processed products to develop white spots. This phenomenon typically occurs during the soldering or cleaning process and appears as white spots or residues on or around the surface of the printed circuit board, pins, and solder joints.

To address this issue, PCBA foundries and electronic material procurement companies have established strong engineering teams that offer a complete IT architecture and supply chain, as well as a scientific quality management system. This ensures that they can meet the unique manufacturing requirements of OEM manufacturers/customers.

The white spots are often formed by reactive materials such as crystalline rosin, rosin mutants, organic and inorganic metal salts, group fluxes, and cleaning agents. These substances are formed during high-temperature soldering. However, most rosin or water-soluble acids have undergone a chemical change from the flux, which makes them harder to dissolve in cleaning agents than their original ingredients.

Pine resin residues can be removed by solvent combinations that achieve swelling and dissolution based on similar dissolution principles and solubility coefficients. However, organic acids react with metals such as tin and lead, and their metal oxides form carboxylates. The higher the temperature, the longer the generation time for these hard metal salts, which can only be removed by ultrasonic cleaning. Therefore, lowering the temperature and shortening the time can reduce the occurrence of such residues.

Denaturation of organic matter after soldering makes it difficult to clean the composition and structure of the flux. Moreover, there are many types of PCB fluxes, which can be chemically interfered with during the PCB production process. The intervention of certain solvents on the flux destroys the original surface quality of the flux, leading to the emergence of white spots.

Due to the various types of white spots that can appear in PCBA processed products, which can impact product quality, it is essential to identify the causes of different types of white spots. They can appear in wave soldering and reflow soldering. The composition of white spots is complex, and it is not easy to predict their formation.

Solutions of White Spots in PCBA Processing

Identification of white spot components in PCBA processing can be done through various methods. These include:

Welding identification: Repeat flux identification but exclude the wave soldering step. If no white spot is found, it is possible that the welding temperature is too high or the welding time is too long.

Cleaning agent/cleaning process identification: After the standard assembly process, allow the PCBA to cool down to room temperature before cleaning. If no white spots are observed, the problem may be related to the cleaning process temperature.

PCB identification: Take out several unplugged bare boards from the problematic batch and clean them with a general cleaning procedure of removing flux. Clean the pre-washed bare boards after the standard assembly process. If no white spots are found, the problem could be that the light board is contaminated. Confirm whether there is a problem with the manufacturing process of the light board.

Flux identification: Take out several uninsured bare boards from the problem batch, do not add flux, and follow the standard assembly process. If there are no white spots, the problem may be related to flux and solder.

Other reasons: Optical methods can be used to detect surface residues, and they can also be observed by solvents such as dripping water or ethanol. If it is soluble in water, it is expressed as an inorganic residue, while if it is soluble in alcohol, it is expressed as an organic residue. Traditional PCBA cleaning methods may have limited impact on some of the refractory leukoplakia covered in this article.

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– Experienced and skilled team

– State-of-the-art equipment

– Strict quality control

– Excellent customer service

– Competitive price