What is the purpose of PCBA cleaning and why do we need PCBA cleaning?
1.Appearance and electrical performance requirements
The most intuitive effect of contaminants on PCBA is the appearance of PCBA. If placed or used in a hot and humid environment, there may be moisture absorption and residue whitening. Due to the widespread use of leadless chips, micro BGAs, chip-level packages (CSPs) and 0201 components in components, the distance between components and boards is shrinking, boards are getting smaller and smaller, and assemblies are becoming denser. In fact, local cleaning can be disastrous due to halide release if the halide is hidden underneath the component or simply cannot be cleaned. This can also lead to dendrite growth, which can result in short circuits. Improper cleaning of ionic contaminants can lead to many problems: low surface resistance, corrosion, and conductive surface residues can form dendritic distributions (dendrites) on the surface of the circuit board, leading to localized short circuits
The main threat to the reliability of military electronics is tin whiskers and metal intercalation. This problem has always existed. Tin whiskers and metal intercalation can eventually lead to short circuits. In a humid environment and with electricity, if there is too much ionic contamination on the component, it can cause problems. For example, the wiring on the board will short out due to electrolytic tin whisker growth, corrosion of the conductors, or a reduction in insulation resistance
Improper cleaning of non-ionic contaminants can also cause a range of problems. It may lead to poor adhesion of the board mask, poor pin contact of the connector, poor physical interference, poor adhesion of the conformal coating to moving parts and plugs. At the same time, non-ionic contaminants may also be wrapped in which the ionic contaminants, and may wrap and bring in other residues and other harmful substances. These are problems that should not be ignored.
2、Three-proof paint coating needs
To make the three-proof paint coating reliable, the surface cleanliness of PCBA must be made to meet the requirements of IPC-A-610E-2010 Level 3 standard. Resin residues that are not cleaned off before surface coating can lead to delamination of the protective layer, or cracks in the protective layer; activator residues may cause electrochemical migration under the coating, leading to coating rupture protection failure. Research shows that by cleaning can increase 50% coating bonding rate.
3、No-cleaning also needs cleaning
According to current standards, the term “no cleaning” refers to the residue on the circuit board is chemically safe, will not have any impact on the board, and can remain on the board. Corrosion testing, surface insulation resistance (SIR), electromigration and other special testing methods are mainly used to determine the halogen/halide content and thus the safety of non-clean components after assembly. However, even with no-clean fluxes with low solids content, there will still be more or less residues. For products with high reliability requirements, residues or other contaminants are not allowed on the board. For military applications, even clean no-clean electronic components are required.