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In what is often mentioned white spot problem in PCBA processing some PCBA processing products may encounter white spot problem?
White dot phenomenon generally occurs in the welding process or cleaning after welding process, mainly for PCB, pins and solder joint surface or the surrounding white spot or white residue.
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Composition of the coating material can be reaction substances, such as crystallization rosin, rosin mutants, organic and inorganic metal salts, group flux, flux or cleaner, as well as other chemicals generated in a high temperature when welding.
However, most of the rosin or water-soluble acid from chemical changes have taken place in the flux, cause its in cleaner than its original composition is more difficult to dissolve.
Generally pine resin residues, according to the principle of similarity of dissolved and solubility coefficient, choice of different solvents can be cleaned and implements the swelling and dissolving purify.
However, organic acid and tin, lead and other metal and metal oxide reaction carboxylic acid salt, and the higher the temperature, the longer.
Can't remove the hard metal salt solvents, need ultrasonic assisted cleaning.
Therefore, by lowering the temperature and shorten the time to reduce the generation of the residue.
In addition, the composition of organic matter degeneration for cleaning after welding flux structure brings difficulties, combined with the PCB flux variety, the family is in the process of PCB production chemical interference, some solvent for flux intervention destroys the flux of the original surface quality.
Make the white spot phenomenon emerge in endlessly, only choose cleaner.
There are many types of vitiligo in given PCBA processing products, the quality of product has a certain influence, it is necessary to find out the reasons of the different types of white spot.
White spots appear in wave soldering and reflow soldering.
The composition of white spot is very complex, its cause is not easy to predict.
Because of the complexity of the wave soldering process control and white dot recognition difficulty, in the process of production can be through the following steps to determine the quality of wave soldering.
PCB circuit board SMT 2.
PCBA processing white spot component identification method (1) welding marks repeat flux, but skip the wave soldering process.
If there is no white point, related to welding temperature too high or welding time is too long.
(2) cleaner/cleaning process identification standard after assembly process, PCBA processing will extend time interval between welding and cleaning, until the temperature down to room temperature.
If there is no white spot, then the problems related to the cleaning process temperature.
(3) PCB identify pieces out of the problem batch has pulled out of naked plate, and remove the flux of the cleaning procedures prewash in general.
Prewash bare plate cleaning after standard assembly process.
If prewash board after the same program without white spots, that problem is that the plate has been polluted.
To determine whether the plate manufacturing process has a problem.
(4) flux identification from the problem batch pieces did not insert the bare plate, don't add flux, it is follow the standard assembly process.
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If there is no white spot, then the problems related to the flux and solder.
(5) other reasons for other reasons for the identification of PCBA processing surface residue, optical methods are available, and also can be observed through a drop of water or solvent such as ethanol.
If the soluble in water, it is represented as inorganic residue, if soluble in alcohol, has said for organic residue.
PCBA coating types, causes and cleaning method of the traditional PCBA cleaning method may be involved in this article some intractable vitiligo limited impact.
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