Whether to clean circuit boards before conformal coating is a well discussed problem.
However, I thought it may be interesting to summarize the reasons for considering the cleaning process before coating as it can be critical to the success of the product in the field.
First, consider that cleaning of a printed circuit board (PCB) before applying conformal coating is normally done for two key reasons:
These are:
– Contamination removal
– Process improvement
They do have different effects on the lifetime of the circuit board. But, they can be equally important.
Lets consider each reason individually.
Contamination removal
Removing contaminants from the surface of a PCB before conformal coating application may be important.
The reason is that the contamination may be harmful to the circuit board during its lifetime.
This contamination could cause long-term reliability issues of the circuit and problems like corrosion could occur that can be devastating to a circuit board performance in the field.
Therefore, cleaning the PCB before conformal coating could be advantageous just to improve reliability.
Process improvement
Cleaning the circuit before application can aid the conformal coating process.
The process can help avoid conformal coating defects like de-wetting and delamination. It can also help promote adhesion of the conformal coating to the PCB (can aid long term reliability).
Therefore, the surface preparation of the circuit can be extremely important, especially where some conformal coatings may have compatibility issues with the circuit board.
Thus, cleaning a PCB before conformal coating could improve the conformal coating quality and minimise defects.
What types of contamination may be present on a circuit board?
Cleaning is used to remove many different types of contaminants from the manufacturing and assembly processes.
Nexus, the independent conformal coating resource, have suggested there are many different types of contaminants that could be required to be cleaned before conformal coating application.
These residues include:
– Board laminate manufacture
– Component manufacture
– Soldering assembly processes (fluxes)
– Glue and ruggedizing processes
– Operator handling (finger prints, hair)
– Machine contamination (oils and greases)
– Environmental contamination (dust)
Many of these residues could be harmful both to the long term reliability and the process.
Therefore, removing the contamination may be a priority.
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