When can I use my circuit board after application of conformal coating?

The term “use” needs to be defined since there are several levels of drying and curing in the conformal coating process. Lets consider these stages:

Stage 1: Tack dry – This is where the coating is dry enough not to be sticky when handled. Acrylic solvent based coatings can be tack dry in less than 10-15 minutes depending on coating thickness, extraction rates, temperature, humidity and solvent type used. However, the coating will be soft to handle and easily damaged.

Stage 2: Fully Dried – This is where the coating is dry enough to handle.This would be good for production if you want to process the PCB and insert it into packaging etc.Note this is not cured. Curing and drying are two different concepts as we will see in Stage 3.

Stage 3: Fully Cured – Drying is where the liquid is removed enough from the coating like water is removed from the clothes you wash. Curing is where the coating changes state. Consider the solvent based acrylic coating. The solvent evaporates from the coating and it dries. However, the resin suspended in the solvent does not change state. In fact, the coating never “cures” but has just dried out. This is very different to a polyurethane which will dry first and then it will cure where it cross links to give chemical resistance. The speed of the cure process is dependent on the coating.

In fact in general a urethane conformal coating, until it cross links, has similar chemical resistance to an acrylic. This is an advantage in repair initially but not good for any environment testing if exposing the circuit board to chemicals in a semi cured state. Therefore, you must ensure it is fully cured before testing.

Obviously, different coatings have different drying and curing mechanisms and this also needs to be considered. A moisture cure silicone certainly has a different cure profile compared to a UV cure polyurethane. So, the key to knowing when you can use your circuit board is to understand what you want to do with it and also understand the material properties of the coating.

For further information on this topic Download the Technical Bulletin Curing and Drying of Conformal Coating, review our Technical Database and Conformal Coating FAQs Section or Contact Us now.

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About Dr Lee Hitchens

Dr Hitchens has been working in the electronics industry and the area of conformal coatings for over 25 years in various areas including sales and technical support. He has also been training people for almost the same amount of time in all areas of conformal coating whether that is materials & equipment selection, process development or troubleshooting to help them solve their particular problem. Recently, he decided that the industry needed a specific place where all of the useful knowledge on conformal coatings could be collated for users to find easily and use in their own production process. So, Nexus was born and he began the Nexus eBook project.

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