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Causes and solutions of white spots in PCBA processing

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

Some PCBA processed products may encounter white spots. White spots usually occur during welding or post-welding cleaning, and are mainly manifested as white spots or white residues on or around the surface of PCB, pin and solder joint. Pcba OEM electronic materials procurement structural parts production SMT processing, pcba manufacturing, machine assembly, machine testing, with a strong engineering team, provide a complete set of IT architecture and supply chain and scientific quality management system, committed to meet OEM/customer different types of manufacturing requirements. White spot substances may be composed of reactive substances such as crystalline rosin, rosin mutants, organic and inorganic metal salts, group flux, flux or detergent, and other chemicals produced during welding at high temperatures. However, most rosin or water-soluble acids undergo chemical changes from the flux, making it more difficult to dissolve in the cleaner than its original composition.

General pine resin residues, according to similar dissolution principle and dissolution coefficient, choose different solvent combinations to achieve swelling and dissolution can be cleaned and removed. However, organic acids react with metals such as tin and lead and their metal oxides to form carboxylate, and the higher the temperature, the longer the formation time. This hard metal salt cannot be removed by general solvent and needs ultrasonic assisted cleaning. Therefore, the generation of this residue can be reduced by lowering the temperature and shortening the time. In addition, the denatination of organic matter after welding brings difficulties in cleaning the composition and structure of the flux. In addition, there are many kinds of PCB family flux, which leads to chemical interference in the PCB production process, and the interference of some solvents on the flux destroys the original surface quality of the flux. Make white spot phenomenon emerge in endlessly, choose to clean agent pertinently only. In view of the existence of various types of white spots in PCBA processing products, which have a certain impact on product quality, it is necessary to find out the causes of different types of white spots. White spots appear in wave soldering and reflow soldering. The composition of the white spot 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 following steps can be used to determine the quality of wave soldering in the production process.

2. Identification method of white spot components in PCBA processing

Welding identification repeat flux identification, but skip the wave soldering step. If there is no white spot, it is related to excessive welding temperature or welding time.

Detergent/cleaning process label

With the standard assembly process, PCBA processing extends the time between welding and cleaning until the temperature drops to room temperature. If there are no white spots, the problem is related to the temperature of the cleaning process.

3. PCB shall identify and remove several unplugged bare plates from the problem batch, and pre-wash them with the general cleaning procedure of removing flux. Pre-washed bare plates are cleaned after the standard assembly process. If no white spots appear after the same process on the pre-washed board, the problem is that the light plate is contaminated. Make sure there is no problem with the manufacturing process.

Remove several uninserted bare plates from the problem batch, do not add flux, but follow the standard assembly process. OEM OEM generation of processing and has a number of highly qualified management personnel and skilled workers, and has international advanced production equipment and complete test technology and scientific quality management system, is committed to meet the requirements of OEM/customer of different types of manufacturing, to provide from the product components procurement to production assembly, the full range of technical support services. If there are no white spots, the problem is related to flux and solder.

(5) other reasons to identify other reasons for residue on PCBA processing surface, which can be detected by optical method, or observed by dripping water or solvents such as ethanol. It is expressed as an inorganic residue if soluble in water, and as an organic residue if soluble in alcohol. Types, causes and cleaning methods of PCBA white spots traditional PCBA cleaning methods may have limited influence on some refractory white spots involved in this paper.