PCBA Tech - Causes and solutions of white spots in PCBA processing

Causes and solutions of white spots in PCBA processing

1. What is the white spot problem often mentioned in PCBA processing

Some PCBA processed productsmay encounter white spots? The white spot phenomenon generally occurs during the soldering process or the cleaning process after soldering, and is mainly manifested as white spots or white residues on or around the surface of or around the PCB, pins, and solder joints. PCBA foundry and electronic materials procurement of structural parts production SMT processing, PCBA manufacturing, machine assembly, machine testing, has a strong engineering team, provides a complete set of IT architecture and supply chain and scientific quality management system, committed to Meet the different types of manufacturing requirements of OEM manufacturers/customers. The composition of the white spot material can be reactive materials, such as crystalline rosin, rosin mutants, organic and inorganic metal salts, group fluxes, fluxes or cleaning agents, and other chemical substances produced during high-temperature soldering. However, most rosin or water-soluble acids have undergone a chemical change from the flux, causing it to be more difficult to dissolve in the cleaning agent than its original ingredients.

Generally, pine resin residues can be cleaned and removed by choosing different solvent combinations to 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 to form carboxylates, and the higher the temperature, the longer the generation time. This kind of hard metal salt cannot be removed by general solvents, and ultrasonic cleaning is required. Therefore, the generation of such residues can be reduced by lowering the temperature and shortening the time. In addition, the denaturation of organic matter after soldering brings difficulties to cleaning the composition and structure of the flux. In addition, there are many types of PCB fluxes, which are chemically interfered during the PCB production process. The intervention of certain solvents on the flux destroys the original surface quality of the flux. The phenomenon of leukoplakia emerges in an endless stream, and only a targeted cleaning agent is selected. In view of the existence of various types of leukoplakia in PCBA processed products, which have a certain impact on product quality, it is necessary to find out the causes of different types of leukoplakia. White spots appear in wave soldering and reflow soldering. The composition of leukoplakia is very complex, and the cause of its formation is not easy to predict. Due to the complexity of wave soldering process control and the difficulty of white spot identification, the quality of wave soldering can be determined by the following steps in the production process.

2. Identification method of white spot components in PCBA processing

1. Welding identification Repeat the flux identification, but skip the wave soldering step. If there is no white spot, it is related to the welding temperature is too high or the welding time is too long.

2. Cleaning agent/cleaning process identification

After the standard assembly process, PCBA processing will extend the time interval between soldering and cleaning until the temperature drops to room temperature. If there are no white spots, the problem is related to the cleaning process temperature.

3. PCB identification Take out several unplugged bare boards from the problem batch and pre-wash them with the general cleaning procedure of removing flux. The pre-washed bare boards are cleaned after the standard assembly process. If the pre-washed board does not show white spots after the same procedure, the problem is that the light board is contaminated. Confirm whether there is a problem with the manufacturing process of the light board.

4. Flux identification Take out several uninserted bare boards from the problem batch, do not add flux, but follow the standard assembly process. The foundry processing has a group of high-quality management personnel and skilled employees, and has the international advanced level of production equipment, complete testing technology and scientific quality management system, committed to satisfying OEM manufacturers/customers of different types of manufacturing Request, provide a full range of services from product component procurement to production assembly and technical support. If there are no white spots, the problem is related to flux and solder.

5. Other reasons To identify other reasons for PCBA processing surface residues, optical methods can be used to detect, and it 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, if it is soluble in alcohol, it is expressed as an organic residue. Types, causes and cleaning methods of PCBA leukoplakia Traditional PCBA cleaning methods may have limited impact on some of the refractory leukoplakia covered in this article.