What is the purpose of PCBA cleaning? Why do we carry out PCBA cleaning?

1. Appearance and electrical performance requirements

The most obvious effect of pollutants on PCBA is the appearance of PCBA. Hygroscopic and residue whitening may occur if placed or used in a hot and humid environment. Due to the widespread use of leadless chips, micro-BGA, chip level packaging (CSP) and 0201 components in components, the distance between components and the circuit board is shrinking, the size of the circuit board is getting smaller and the assembly density is increasing. In fact, if the halide is hidden beneath the component or cannot be cleaned at all, local cleaning can be disastrous due to the release of the halide. This can also lead to dendrite growth, which can lead to short circuits. Improper cleaning of ionic contaminants can lead to many problems: low surface resistance, corrosion, and conductive surface residues can form dendritic distribution (dendrites) on the circuit board surface, resulting in local circuit short circuit.

The main threat to the reliability of military electronic equipment is tin whiskers and metal compounds. The problem persists. Tin whisker and metal compounds will eventually lead to a short circuit. In humid environments and with electricity, if there is too much ion contamination on the component, it can cause problems. For example, the wiring on a circuit board will short-circuit due to growth of electrolytic tin whiskers, corrosion of conductors, or a reduction in insulation resistance. Improper cleaning of non-ionic contaminants can also cause a series of problems. May result in poor adhesion of circuit board mask, poor contact of connector pins, poor physical interference, and poor adhesion of conformal coating to moving parts and plugs. At the same time, non-ionic pollutants may also encase ionic pollutants, and may encase and carry other residues and other harmful substances. These are issues that cannot be ignored.

2, three anti-paint coating needs

In order to make the coating reliable, the surface cleanliness of PCBA must meet the requirements of IPC-A-610E-2010 level 3 standard. Resin residues not cleaned before surface coating can lead to delamination of the protective layer, or cracks in the protective layer; Activator residues may cause electrochemical migration beneath the coating, resulting in coating rupture protection failure. The study shows that the adhesion rate of coating can be increased by 50% by cleaning.

3, clean also need to clean

According to current standards, the term "clean free" refers to residues on a circuit board that are chemically safe, do not affect the circuit board in any way, and can remain on the circuit board. Special detection methods such as corrosion detection, surface insulation resistance (SIR), and electromigration are mainly used to determine halogen/halide content, thus determining the safety of uncleaned components after assembly. However, even with a no-wash flux with a low solid content, there will still be more or less residue. For products with high reliability requirements, no residue or other contaminants are allowed on the circuit board. For military applications, even clean - free electronic components are required.