My Customer has asked me to bake my printed circuit boards for 2 hours at 90 degrees C before applying the conformal coating. What is the reason for this?

There are several answers to the question and most of them are really vague and to be honest possibly short of scientific basis. Talking to Phil Kinner, an expert in conformal coating, he came up with two reasons for possibly doing this:

1. To overcome moisture uptake of the boards between cleaning and coating if significant delay between the two processes. High levels of moisture can create havoc with certain solvent-based materials developing their adhesion, or lead to blushing, where coating becomes cloudy, hazy or milky in appearance. This also can lead to bubbling with moisture curing mechanisms occurring at a rate greater than the permeation of by products, eg CO2 through the film.

2. To help prevent excessive capillary flow or dripping on inversion with low viscosity solvent-based materials. This is if the boards is still hot from the bake process. The theory being that the heat drives the solvent-off quicker and builds the viscosity faster. This works well with primer or ‘dusting’ layers, less well with traditional conformal coating processes.

To find out more click Conformal Coating Application Process FAQs

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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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