Application of protective coating PCB varnish in Electronics manufactory.
Author Dmitrii KhramtsovPosted 20 May 2024
Updated 14 December 2024
In my practice, the main emphasis is on the lacquer for protection PCB varnish coating electronics PCB printed circuit boards: Humiseal 1a33 and its variants. Humiseal 1a33 is elastic and convenient to use. Explore the market of available varnishes and use what best suits your needs.
How is protective varnish coating applied to electronics PCB?
1. The air bubbles in the layer of applied moisture protection are considered a defect. The defect is eliminated either by a vacuum chamber or a chamber with less than atmospheric pressure. Or by applying varnish made by immersion in a reasonably liquid varnish with good fluidity. The varnish should be like water. Each type of varnish has its solvents. Check with your varnish manufacturer or supplier for details about solvents.
2. There is no point in applying more than two layers of coating. Due to its large thickness, the varnish greatly loses its strength during rapid temperature transitions from negative to positive zones. Even the highest-quality coating has a coefficient of thermal expansion, which leads to cracks in the layers.
3. That even 1 correct layer of protective varnish can crack at minus 65 C° (149 °F). Therefore, it is necessary to test the PCB lacquer coating in a heat chamber.
4. Protective varnish coatings for electronics are not applied to printed circuit boards without being washed in professional cleaning systems with appropriate cleaning agents. This is because the residues of soldering flux and other chemicals on the printed circuit boards do not allow a good level of adhesion. Test kits are available to check flux residues after rinsing. Of course, you can apply varnish despite this caveat, but this printed circuit board cannot be used in critical devices for aviation, medicine, military equipment, and other areas.
5. Always use air hoods. Not filters, but hoods. There is no need to breathe fumes.
6. If your Printed Circuit Board will be operating in an area with very low temperatures, it is best NOT to use the varnish dipping method, as the shrinkage of the varnish may cause broken solder joints. Also, in high-temperature areas, the varnish may leak, and this must be taken into account. Understanding the methods and limitations of varnish application will ensure better moisture protection and stable operation of electronics in various environmental conditions. I recommend using IPC standards to better understand coating techniques.
2. There is no point in applying more than two layers of coating. Due to its large thickness, the varnish greatly loses its strength during rapid temperature transitions from negative to positive zones. Even the highest-quality coating has a coefficient of thermal expansion, which leads to cracks in the layers.
3. That even 1 correct layer of protective varnish can crack at minus 65 C° (149 °F). Therefore, it is necessary to test the PCB lacquer coating in a heat chamber.
4. Protective varnish coatings for electronics are not applied to printed circuit boards without being washed in professional cleaning systems with appropriate cleaning agents. This is because the residues of soldering flux and other chemicals on the printed circuit boards do not allow a good level of adhesion. Test kits are available to check flux residues after rinsing. Of course, you can apply varnish despite this caveat, but this printed circuit board cannot be used in critical devices for aviation, medicine, military equipment, and other areas.
5. Always use air hoods. Not filters, but hoods. There is no need to breathe fumes.
6. If your Printed Circuit Board will be operating in an area with very low temperatures, it is best NOT to use the varnish dipping method, as the shrinkage of the varnish may cause broken solder joints. Also, in high-temperature areas, the varnish may leak, and this must be taken into account. Understanding the methods and limitations of varnish application will ensure better moisture protection and stable operation of electronics in various environmental conditions. I recommend using IPC standards to better understand coating techniques.
Methods of applying varnish and protective coating to Printed Circuit Boards.
Method 1. Brush. Lowest quality. The brush is a bubble generator. When using a brush, you must protect areas on the PCB where varnish could stain the connectors. To cover, you can use tape or spot masks. Despite all the shortcomings, it fulfills the task of protection.
Method 2. Completely immersed in varnish. Immerse the circuit board in a container of varnish for a minute. The method is long but relatively cheap and of very high quality. In a minute, the liquid varnish penetrates under the parts and displaces the air. Varnishes are generally neutral to metals and chemicals. After removal, you need to give a minute for the residue to drain back into the container. The work is carried out in a fume hood and it is also necessary to place hangers with hooks for hanging and drying printed circuit boards.
Method 3. Robotic systems for applying varnish to printed circuit boards. The method is very fast. Uniform and precise application of varnish only to the desired areas, eliminating accidental application. This method is most often used in large factories to speed up the production of printed circuit boards.
Method 4. Spraying protective varnish onto printed circuit boards using a spray bottle or a can. A fast and effective method suitable for small batches, for testing and electronics development.
Thanks for reading! Create high-quality electronics☺
Method 2. Completely immersed in varnish. Immerse the circuit board in a container of varnish for a minute. The method is long but relatively cheap and of very high quality. In a minute, the liquid varnish penetrates under the parts and displaces the air. Varnishes are generally neutral to metals and chemicals. After removal, you need to give a minute for the residue to drain back into the container. The work is carried out in a fume hood and it is also necessary to place hangers with hooks for hanging and drying printed circuit boards.
Method 3. Robotic systems for applying varnish to printed circuit boards. The method is very fast. Uniform and precise application of varnish only to the desired areas, eliminating accidental application. This method is most often used in large factories to speed up the production of printed circuit boards.
Method 4. Spraying protective varnish onto printed circuit boards using a spray bottle or a can. A fast and effective method suitable for small batches, for testing and electronics development.
Thanks for reading! Create high-quality electronics☺