Nowadays, the design of electronic assembly tends to be miniaturized, with smaller devices and smaller spacing, pins and pads are getting closer and closer, and the existing gap is getting smaller and smaller. Pollutants may be stuck in the gap, which means that if relatively small particles remain between two pads, it may cause potential adverse effects of short circuit. In the past two years, the electronic assembly industry has higher and higher requirements for cleaning, not only for products, but also for environmental protection and human health. As a result, many cleaning equipment suppliers and solution suppliers have emerged, and cleaning has become one of the main contents of technical exchange and discussion in the electronic assembly industry. PCBA proofing and cleaning can improve the quality of the circuit board, otherwise it will affect the stability of the product
1、 Three proofing paint requirements: before the surface coating of PCBA proofing, the resin residue that has not been removed will lead to delamination or fracture of the protective layer; The residue of active agent may lead to the electrochemical migration under the coating, which leads to the failure of anti cracking protection of the coating. The results show that the adhesion rate of the coating can be increased by 50% by cleaning.
2、 Cleaning free also requires cleaning: according to current standards, the term “no cleaning” refers to that residues on the circuit board are safe from a chemical point of view, and will not have any impact on the circuit board production line and can be left on the circuit board. Corrosion, sir, electromigration and other special detection methods are mainly used to determine the halogen / halide content, and then determine the safety of non cleaning components after assembly.
3、 Appearance and electrical performance requirements: the most intuitive impact of PCBA proofing pollution is appearance. If it is placed in high temperature and high humidity environment or used, the residue may absorb water and turn white. Because of the wide use of lead-free chips, micro BGA, chip level packaging (CSP) and 01005 in components, the distance between components and circuit boards is reduced, the size is reduced and the assembly density is increased. If halides are hidden under components that cannot be cleaned, local cleaning can have catastrophic consequences due to the release of halides.
The most direct effect of pollutants on the preparation of PCBA is the appearance of the sample preparation. If placed or used in the high temperature and humidity environment, the residue may appear moisture absorption and whitening. Because of the large number of use of leadless chips, micro BGA, chip level packaging (CSP) and 0201 components in the components, the distance between the components and the circuit board is shrinking, the size of the board becomes smaller and the assembly density is increasing. In fact, if halides are hidden under the components or cannot be cleaned at all, local cleaning may cause catastrophic consequences due to the release of halides. It also causes dendrite growth, which may cause short circuit.
More or less residue will be left when PCBA is used as a clean free flux with low solid content. For products with high reliability requirements, no residues or contaminants are allowed on the circuit board. For military applications, it is even necessary to clean electronic components. The assembly of PCBA proofing of general electronic products shall pass SMT + THT process, during which the welding process shall be conducted by wave peak welding, reflow welding, manual welding and other welding processes. No matter what welding method, the assembly (electric assembly) process is the main source of assembly pollution. Cleaning is a process of dissolving and removing welding residues. The purpose of cleaning is to extend the service life of products by ensuring good surface resistance and preventing electric leakage.
