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Curing Conformal Coating

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Curing Conformal Coating | 5 June, 2008


I've been looking into UV cureable conformal coating and the UV ovens but a chemist I know is very negative about this. He suggest by heating standard conformal coating to 90deg for a couple of minutes will make the product good enough to handle/pack(all what UV curing does). He also thinks UV conformal coating is unstale (must store it at a particular temperature, has limited shelf life, will probably go off before we use it all) I am in Australia, so we'll have to import it in 40lb drums from loctite @ $2.5k each.

What I don't get is; UV conformal coating is more expensive, UV curing oven, i think, are more expensive but why is it so widely used in the industry when a cheaper more robust conformal coating can be used with a cheaper oven?

What am I missing?

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Curing Conformal Coating | 5 June, 2008

Addressing your points: * "UV conformal coating is more expensive" => You're correct, uV costs 1.7X solvent-based silicone. This high purchased material cost is counter balanced by uV requiring lower thickness due to higher solids and that 60 to 80% of a solvent coating is volitile and goes up the pipe between application and cure. Bottom line: Material cost/board, solvent costs 2.5X uV * "UV curing oven, i think, are more expensive" => Not sure what you're considering, but for similarly configured, high volume [50k board/year] coating operation the capital equipment for a light based cure is less than solvent.

Your analysis doesn't consider: * uV has virtually no cure time, solvent adds a day or so to throughput * uV equipment requires less floor space * Maintenance of dispensing equipment for uV is simpler because, because unlike solvent coatings, uV coating does not cure on the equipment * Unlike uV, solvents present substantial personnel hazard, the degree is dependent on the material. Compare the MSDS * Typical energy, labor overhead/year, solvent costs 2.3X uV * Total cost per year, solvent costs 2.4X uV

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Curing Conformal Coating | 5 June, 2008

Also coating costs depends on solids content vs final dry film thickness. Some newer UV coatings are 100% solids, so what you put down you get on the PCB after cure, use no solvents at all. So a cost to look at are qty of PCB per litre of material. Typically 100% SOlids coatings cover up to 40 m2 vs typical thinned down coatings - 30-40% solids, rest is solvent that you have to pay for that evapourates up your oven exhaust. If you spray the coating, is worse with typical coatings because you have to thin down more again - more solvent - reducing solids content, and increasing wet-film thickness making drying slower and other process problems.

100% UV coatings can be more cost effective - all depends on qty of PCB you need to process, space in your factory for equipment, UV cure vs thermal ovens etc

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Curing Conformal Coating | 6 June, 2008

What about shadow effects? How do you cure UV coat under components?

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Curing Conformal Coating | 6 June, 2008

Shadowing is a concern in uV coatings and adhesives. Look here:

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Curing Conformal Coating | 9 June, 2008

Shadow cure effects are dealt with by post cure mechanisims. New UV Coatings should have one, either heat or moisture cure.

Basically UV primary cure starts off cure process, allows handling of the products.

But UV is not suitable for all products and processes, depends on overall situation. But UV cureables have advanced in recent years to be a choice for low volume vs high volume traditionally.

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