The PCBs after manufacturing and assembly are highly prone to contamination which in turn reduce the shelf life of PCBs. The conformal coating is the protective layer made of mixture of different ingredients, to keep PCBs safe from erosion, moisture, contamination, oxides and other particles that can lower the quality of PCBs and greatly decrease performance or even render PCB useless.
The conformal coating can be applied in different ways on PCB surface. The conformal coating will become hardened and transparent layer upon PCB that gives insulation, anti-aging, moist proof and dust proof advantages to PCB. High operating temperature and stringent environmental conditions like shock, vibrations, chemical, inks and acids can badly affect the PCB without conformal coating and can permanently damage or fail the PCB.
Why Conformal Coating Necessary. .?
As discussed above, there are many factors that can adversely affect the PCB performance if conformal coating is not applied. Conformal coating actually is a preventive coating that functions as protective measure to protect PCBs from external contaminants that may occur even during the manufacturing of PCBs like flux and other etching chemicals and agents. It prevents the PCB from mechanical vibrations, thermal shocks and high temperature due to environmental conditions or PCB high operating temperature. It increases the reliability and ensures proper functionality of PCBs.
As we all know that moisture is not good for metallic parts, as we observe that areas / locations that are close to sea, have high levels of humidity in air as compared to other areas in cities. So this humidity level will create oxidization in metallic parts and components. PCBs are totally made of metallic parts like copper, silver and aluminum main metals used, hence these metals get reacted with moisture in air hence rendering the PCB to decompose at accelerated pace and conductors get eroded. The copper will turn green due to these water vapors and elevated oxygen levels.
However the conformal coated PCBs are far more protected from this high levels of humidity and water vapors that can be present in our environment where PCBs are used. The conformal coating will prevent the oxidation and deterioration of conductors on PCB hence increasing the life of PCB.
Another most important reason why conformal coating is necessary is pollutant or contaminations. These contaminants can be solid dust particles that can stuck in the tiny spaces in PCB SMT components and can become short-circuit. Other handling pollutants can be human oil, finger prints and food particles. The surrounding where the PCB is being kept or used also contributes to pollutants like spray, grease, oil, fuel spill over, and acid fumes exposure.
The technicians on field must be trained to properly handle electronic equipment’s PCBs by wearing gloves, not to spit and spill liquid and avoid eating food while handling PCBs. PCBs without conformal coating, under these rigorous environmental conditions will get easily damaged and irreversible electronic failure in respective electronic device or equipment.
Pollutants are mainly caused by the imperfection in PCB manufacturing setup like improper cleanliness and chemical residues being uncleansed during electroless plating or etching process.
It is highly recommended to clean the PCB thoroughly before applying conformal coating.
Which PCB Applications Use Conformal Coating:
Nowadays, quality is the best policy. If the quality of the end product is compromised then there is a strong chance that your customer will not order PCB manufacturing or assembly again from you. Hence quality is on top of everything.
Having said that, no matter how expensive is the conformal coating (by the not much expensive), it has become the important part of final finishing stage of PCBs after manufacturing. Almost every industry that has electronic equipment, machines, instrument, devices based on Printed Circuit Boards (PCBs) use conformal coated PCBs.
- Consumer Electronics
The consumer electronic products are highly prone to contamination and dust particles that may cause due to bad handling of PCBs like spill-over of water, oil, chemical, detergent and other substances.
- Automotive Industry
The PCBs used in car electronics, audio circuits, AM/FM circuits, front deck, LED light circuits are all vulnerable to vibration and shocks. The conformal coated PCB will be protected from harsh environment and will last long
The aerospace environment is full of radiation, shocks and high temperature. Conformal coating on aerospace PCBs is highly recommended.
The electronic devices installed on ships, boats and Navy equipment are all highly affected by elevated humidity conditions. Hence conformal coated PCBs for navigation and said equipment is highly recommended.
- Medical Electronics and Microbiology Instruments
These sensitive electronic instruments are based on delicate PCBs that require to function smoothly and consistently for long life. This is only possible with conformal coating on PCBs of medical electronic devices to protect them from accidental splash of harsh acids or bases or hazardous chemicals used in labs.
How to Apply Conformal Coating:
There are mainly two ways to apply conformal coating at the PCB manufacturing facility.
Manual Brush Coating:
The manual brush coating can be a cost effective solution but can be time taking process. A skilled technician who can smoothly and uniformly brush the conformal coating on PCB surface is recommended.
Manual Aerosol Coating:
A specialized spray room where external contaminant are minimal should be used. A skilled technician with aerosol in hand can spray manually for small scale production of PCBs in cost effective manner. Do not shake the aerosol before spraying as it will cause bubble formation and transferred to board. Keep the PCB at 45O to the surface and distance between the aerosol and PCB should be 20-30 cm, and spray the conformal coating in zig-zag manner from top to bottom, then rotate the board at 90O and repeat until the boars is rotated complete 360O. This process is done to ensure uniformity of conformal coating and that every single point on PCB is coated uniformly
Manual Atomized Spray Coating:
The atomized spray coating is the same process as aerosol coating, but it is much quicker and efficient method. Proper ventilation must be ensured. Proper viscosity and correct ratio of air and material must be ensured.
Automated Dip Coating:
This method is performed by automated robot at very slow pace to ensure proper and uniformly coated PCB. In this method, if you want some parts of PCB not to be coated then you can mask them initially and then initiate the dip coating. After dip coating, the mask layer has to be removed. Since masking and unmasking and process itself is all time taking and material for mask is also wasted hence not recommended for cost effective solution
Automated Selective Coating:
The automatic coating method is performed by robotic hands where the pre-program is fed in the robot memory to tell which portions of PCB to coat and which to not coat. Robots do this task accurately, without getting tired and consistently repeating the same task every time