PCBA components boards, having undergone processes such as SMT reflow soldering, DIP wave soldering, or selective wave soldering, invariably contain residues of flux and solder paste. Despite the term “no-clean” associated with modern electronic chemicals such as solder paste and flux, it does not indicate the quantity of residues left on the PCBA components board but rather defines residues that can maintain electrical performance within specified temperature, humidity, and time ranges under normal environmental conditions. To enhance the safety and reliability of PCBA components boards to higher technical standards, many manufacturers employ various methods to clean them:
- Manual Cleaning: Many companies employ manual cleaning methods, which often fail to completely remove residues from the board surface. Cleaning with brushes dipped in solvent or other cleaning agents at specific points of residue concentration not only fails to achieve thorough cleaning but also spreads residues from concentrated points to larger areas, exacerbating the potential hazards. Most residues remain on the PCB, and if the post-soldering characteristics cannot perform well under temperature and humidity conditions, it may lead to serious defects such as electrochemical corrosion and chemical migration.
- Full Cleaning Process After Component Soldering: This process involves immersing the PCB into a cleaning solution and performing rinsing using spray or ultrasonic methods to achieve uniform and thorough removal of potential residues on the components. However, the choice of cleaning method or material affects the cleanliness of the board surface. Currently, there are two common methods for evaluating surface cleanliness in the industry: visual inspection, including observation under magnifying glasses or microscopes, and surface ion contamination. It is important to note that whether it is solder paste residues or flux residues, the design of these products by manufacturers is based on no-clean methods to achieve no-clean functional technical standards.
Of particular concern is incomplete cleaning after rinsing. Since most components of flux or solder paste residues are resin, which is relatively easy to dissolve or decompose with solvent-based or water-based cleaning agents, when this resin portion is decomposed or dissolved, it may expose salts or other components of residues in the flux, leading to more serious hazards. In fact, in these flux or solder paste products, the resin acts as a carrier, and the activators, organic acids, and organic acid salts are melted into the carrier. After the resin is washed away, these organic acids and organic acid salts, which are not easily washed away, are easily exposed to the air. With the passage of time, they can cause electrochemical and corrosive hazards, resulting in phenomena such as whitening, greenish discoloration, or blackening, leading to corrosion of circuits and devices, thereby compromising the electrical performance of the component PCB board.
