In general, the assembly of PCBA boards for electronic products should go through the SMT+THT process, which should go through wave soldering, reflow soldering, manual soldering and other welding processes. No matter what type of welding is used, the assembly (electrical assembly) process is the main source of assembly pollution.
Contaminants are defined as any surface deposits, impurities, slag inclusions and adsorbates that reduce the chEMIcal, physical or electrical properties of PCBA to unacceptable levels. It mainly includes the following aspects:
(2) During the production and manufacturing of PCBA, solder paste, solder, solder wire, etc. shall be used for welding. The flux will produce residues on the PCBA board surface during the welding process, which is the main pollutant;
(3) Hand MARKs produced in the process of manual welding, wave soldering process will produce some wave soldering claw foot marks and welding pallet (fixture) marks, and the PCBA surface may also have different levels of other types of pollutants, such as plugging glue, residual glue of high-temperature tape, hand marks and flying dust;
(4) Dust in the workplace, vapor and smoke of water and solvent, micro particulate organic matter, and the pollution of charged particles attached to PCBA caused by static electricity.
Why should PCBA be cleaned
In the past, people did not know enough about cleaning, mainly because the PCBA assembly density of electronic products was not high, and they believed that the residual flux was non-conductive and benign, and would not affect the electrical performance. Today's electronic assembly design tends to be miniaturized. SMAller devices, smaller spacing, pins and pads are getting closer and closer. The existing gap is getting smaller and smaller, and pollutants may be stuck in the gap, which means that if smaller particles are left between two pads, they may cause potential defects of short circuit.
According to the analysis and statistics of PCBA electrical equipment quality problems provided by the Reliability Research and Analysis Center of China Saibao Laboratory, the short circuit, open circuit and other late use failures caused by corrosion and electromigration account for 4%, which is one of the major killers of product reliability.
The pollution may directly or indirectly cause the potential risk of PCBA, such as the organic acid in the residue may cause corrosion to PCBA; During the electrification process of the electric ions in the residue, because the existence of the potential difference between the two pads will cause the movement of electrons, it is possible to form a short circuit, making the product invalid; Residues will affect the coating effect, which will cause problems of non coating or poor coating; It may not be found for the time being. After the change of time and ambient temperature, the coating cracks and warps, causing reliability problems.
It can be seen from the constantly developing electronic product market that modern and future electronic products will become smaller and smaller, and the requirements for high performance and high reliability will be stronger than ever before. Thorough cleaning is a very important and highly technical work, which directly affects the working life and reliability of electronic products, as well as environmental protection and human health. PCB manufacturers, PCB designers and PCBA processors will explain the contamination and cleaning of PCBA boards.