How do UV cure conformal coatings differ to solvent and water based coatings?
UV cure conformal coatings cureswith UV radiation and therefore the material is almost instantly cured if the right light source is used.
The UV light you need for curing UV conformal coatings can be a mix of UVA, UVB and most importantly UVC. this will depend on the manufacturers formulation. However, the radiation can be dangerous if exposure is not controlled due to its high energy. Therefore, the UV light must be contained within a suitable system with safeguards against exposure. Conveyor UV cure ovens like the systems SCH offer are built to ensure exposure is avoided.
Other benefits beyond the fast cure are that UV cure coatings generally do not contain solvents or water within it meaning 100% of the product is coating and the product is classed solventless. Therefore, there are another two advantages. First, what you deposit when coating is what remains after curing. Second, you can reduce your solvent (VOC) emissions which can be important.
For instance, when you spray UV 40 it does not reduce in thickness like solvent and water based coatings, which are a blend of resin, chemicals and most importantly, the carrier solvent or water. You could spray a wet film thickness of 100 microns (0.1 mm) down and for solvent and water based coatings, the solvent and water “evaporate” leaving a thinner dry film thickness of approx 30-40 microns. The rest of the coating has volatised off into the atmosphere and is wasted. There is no evaporation with UV40 so if you coat 100 microns it dries 100 microns. Therefore, waste can be minimised.
Another important factor to consider for UV cured coatings are their secondary cure mechanism. This means that any coating not initially fully cured with the UV light will still continue to finish curing on it own. This is important because of shadowing effects which can be detrimental in curing. If you coat a PCB with a VU cure material some coating could get into areas where there is no way the UV light can get to it for curing. The coating is effectively in shadow from the UV radiation. The coating could then stay liquid which is not good (most coatings are conductive whilst wet and shorting on the PCB can occur where electricity can travel where it shouldn’t. Think of water and electricity. They don’t mix!). Therefore, a secondary cure mechanism is critical.
For many coatings, the secondary cure mechanism is moisture from the air causing the coating to cure. However, this is a much slower process and can take hours. This also means you need to handle the material carefully in storage and loading since exposing the coating to too much air can start the cure mechanism prematurely.
All these positive points mean for the high volume markets like the automotive industry this is a very important material with advantages such as speed of cure and no solvents.
click UV cure conformal coatings FAQs for further information on this area.