Although it tends to take place at the end of the line, the application of varnish must be considered from the design phase of the board. This is the firm belief of Emilie Morice, Process Engineer at the Electronics activity of LACROIX, which varnishes some 30,000 printed circuit boards per year in the French factory.
What is the purpose of the varnishing stage?
Varnishing is the primary mean of strengthening the boards, serving to protect them in their operating environment so that they can withstand given conditions in terms of humidity levels or high temperatures, for example. This operation, referred to as ‘tropicalisation’, takes place at the end of the manufacturing process. It involves applying a very fine coat of varnish, just 30 to 70 microns in thickness. This extends the lifespan of the boards and makes their operation more reliable in environments not suited to electronics.
What are the different varnishing methods?
Four methods can be used to varnish a board:
– automatic (or selective) varnishing
– spray varnishing
– dip varnishing
– brush varnishing
We choose the method best suited to the design of the board and the annual manufacturing volumes. Selective varnishing, in addition to being automatic and therefore more repeatable, eliminates the need for masking. Spray or dip varnishing require masking but have the advantage of being able to reach areas not accessible by a robot.
There are also four different types of chemicals:
– acrylic, which offers quite basic protection
– silicon, for high temperatures and humidity
– polyurethane, more resistant to chemical products
– epoxy, rarer
The Electronics activity of LACROIX employs all these techniques and chemicals in its French factory.
Which varnish is best suited to the aeronautical industry?
It all depends where the board will be located, but acrylic is often chosen. A decision tree is used to select the chemical best suited to the need. It is not advisable to apply a polyurethane varnish, which is difficult to repair, if an acrylic varnish corresponds perfectly to the protection required.
Is varnishing a key stage in the manufacture of boards?
It is indeed a very important stage, which must be considered from the design phase. The process involves constraints which need to be anticipated, even if this means reviewing certain aspects of the board’s design. Poorly prepared varnishing requires more handling and can therefore push up costs! Overlooking the importance of this stage can lead to retouching and quality problems, or reduce the area covered by the varnish. At the Electronics activity of LACROIX, luckily we own a design center which is particularly aware of and sensitive to the issue, since we regularly discuss practical constraints.
How is equipped Saint-Pierre-Montlimart’s plant?
We are equipped with automatic application machines. There is also an area in the workshop dedicated to masking and two manual application booths. We also have a 3D printer, enabling us to produce our own masking caps, which is one of our concrete Smart Industry applications.