Technical Bulletin December

       

Technical Bulletin December

     

What is UV Radiation?

   

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?

    The UV lamps used in the IB100 and 101 booths for conformal coating inspection is UVA   radiation. 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 can be 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 neded 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. Therefore, UVC must be contained within a suitable system with safeguards against exposure. UV Cure conveyors like the systems SCH offer are built to ensure exposure is avoided.

   

What do we provide?

  SCH Technologies can offer conformal coating services, equipment, consultation and Humiseals great range of conformal coating materials. We will be happy to answer any of your   questions and we’ve got the experience to solve any of your conformal coating headaches. Don’t hesitate to contact us with the details on the following page and we’ll help to ease the pain of conformal coating.

   

   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.

     

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 is minimized.

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.

Another important factor for the UV 40 coating is its very effective secondary cure mechanism. This means the coating can cure without the aid of UV light. This is important because of shadowing effects which can be detrimental in UV materials.

UV 40 doesn’t crack under the typical stress trials that are carried out. It also has excellent chemical resistance so is ideal to stop chemical attack.

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 ideal!. Therefore, a secondary cure mechanism is critical to ensure correct processing. For UV 40, the secondary cure mechanism is moisture from the air causing the coating to cure within a sensible timeframe.  

This means UV40 is a very important material for the high volume markets like the automotive industry 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.

SCH Technologies is a Trading Name of SCH Services Limited Newburgh Building, McLintock Way, Barnsley, South Yorkshire. S70 6BF Tel: +44 (0)1226 297711 Fax: +44 (0)1226 297733 www.conformalcoating.co.uk

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