Questions About Materials
Waterbased Coatings
Can I use water based coatings in a dip system?
I have been told water based coatings don’t adhere as well to PCBs. Is this true?
UV Coatings
What type of UV light is used in Conformal Coating Inspection and the spray booths?
What is Humiseal UV 40 and how does it differ to solvent and water based coatings?
Do I need a conveyorised UV cure system to process my UV 40 material?
Can I use water based coatings in a dip system?
Water based coatings like Humiseal 1H20 AR3 are perfect for dip coating systems. Since they have a very low VOC content (<7%) they have minimal extraction requirements and of course very little losses from solvent evaporation.
The only caution that needs to be taken is to check the fittings on the pipe work of the dip system to check that the fittings are stainless steel and not brass. This is because the DI water in the coating will cause corrosion on the part and turn the coating green in a matter of weeks!
I have been told water based coatings don’t adhere as well to PCBs. Is this true?
It can be true that water based coatings can be less effective in adhesion compared to solvent based coatings. This is because the solvents in the coating “clean” the surface of the board more effectively than water and bonding of the coating to the board is slightly improved. However, in most cases the water based coating wets perfectly well and there is no issue. If adhesion is a factor, then SCH have a range of coatings in the Humiseal range that could be selected to help.
Ultra-violet radiation forms part of the electromagnetic spectrum and is invisible to the naked eye. The wave length of UV radiation varies from 100-400nm, finishing in the blue portion of visible light.
In terms of energy output, the shorter the wavelength of the UV radiation the higher the energy of the light. These energy levels can be subdivided into 4 specific regions:
UVA-Radiation (400-315nm)
UVB-Radiation (315-280nm)
UVC-Radiation (280-200nm)
VUV-Radiation (200-100nm)
What type of UV light is used in Conformal Coating Inspection and the spray booths?
The UV light used in the IB100 and 101 inspection booths for conformal coating inspection is UVA radiation using black light blue lamps. These lamps filter the majority of visible light leaving only UVA radiation which is perfectly safe when correctly positioned in the booths.
What is Humiseal UV 40 and how does it differ to solvent and water based coatings?
Humiseal UV 40 is a single part conformal coating that cures with UV radiation and therefore is almost instantly cured if the right light source is used. Unfortunately, the UV radiation needed differs from UVA lamps used in our inspection systems which will not cure the coating.
The UV light you need for curing UV 40 is a mix of UVA, UVB and most importantly UVC. However, UVC radiation can be dangerous if exposure is not controlled. Generally, if you can see UVC light, it could make you blind! Therefore, UVC 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.
UV 40 contains no solvents or water within it meaning 100% of the product is coating and the product is classed solventless. Therefore, one of the advantages is that what you deposit when coating is what remains after curing.
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 volatized 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 minimized.
Another important factor for the UV 40 coating is its secondary cure mechanism. This means the coating can cure without the UV light. This is important because of shadowing effects which can be detrimental in curing.
If you coat a PCB with UV 40 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 UV 40, 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.
Once cured the UV 40 coating is extremely flexible compared to other UV coatings. This makes it almost unique. Normal UV coatings have poor flexibility and so can crack. UV 40 doesn’t under the typical stress trials that are carried out. It also has excellent chemical resistance so is ideal to stop chemical attack.
This means 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.
Do I need a conveyorised UV cure system to process my UV 40 material?
Ideally you do due to the nature of the UV light source needed to cure the coating. The UV light is highly focused in a small strip / area and the conveyor moves the PCB past the light, curing the coating successfully. If you use a less intense static light box it has a more diffuse strength due to it having to cure a larger area all at once and is slower at curing the coating. This in turn means the coating has a different reaction and can cure unsuccessfully.