For the majority of small and medium-sized contract manufacturers or production plants, cost considerations often lead them to use traditional manual brushing cleaning methods. This involves using an antistatic brush dipped in cleaning agent to brush the PCB. The PCB is tilted at a 45° angle, and the brush is moved from top to bottom, allowing the cleaning agent to dissolve residues and flow downward. This method is mainly used for localized cleaning or for cleaning PCBA with components that cannot be cleaned. Although this method is simple, it is inefficient and consumes a large amount of cleaning agent.
Recognized contract manufacturers or large-scale production plants are gradually reconsidering their cleaning processes and are equipping themselves with offline or online cleaning machines to replace manual cleaning with equipment cleaning to ensure the quality of PCBA cleaning.
During the actual cleaning process, it is common to encounter PCBA assembled through manual soldering, which may exhibit whitening on the board surface after placement. The white marks are prominently distributed around the solder joints, or in the case of wave soldering, dark stains may appear, severely affecting the appearance acceptance and not meeting the standards. The white residue on the PCBA is a common contaminant, mostly by-products of flux. Common white residues include flux residues, unreacted activators, and reaction products of flux with solder, such as lead chloride or lead bromide. These substances expand upon absorbing moisture, and some substances undergo hydration reactions with water, making the white residues increasingly visible. Removing these residues from the PCB surface is exceptionally challenging. If overheated or exposed to high temperatures for a prolonged period, the problem becomes more severe. Infrared spectroscopy analysis of flux and residues on the PCB surface before and after the soldering process confirms this process.
During assembly, electronic accessories may use flux containing halogens (although most suppliers provide environmentally friendly flux, flux completely free of halogens is still relatively rare). After soldering, residues of halide ions (F, Cl, Br, I) may remain on the board surface. These halide residues themselves are not white, nor are they enough to cause the board surface to turn white. When these substances encounter water or moisture, they produce strong acids. These acids begin to react with the oxide layer on the solder joint surface, resulting in the formation of acid salts, which are the white substances observed.
