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The conformal coating process, like any other processes, has different variables, inputs, and outputs. In order to be able to control the results of your application (outputs), we need to fully understand how each variable affects the process. 

The importance of the variables

To get the right amount of liquid, thickness, right coverage, no contamination on keep out areas, etc., you need to identify and understand the variables of the process.

The most important variables:

• Viscosity
• Flow
• Machine parameters (speed and Height)
• Curing method

In this blog, we will concentrate on reviewing the first variable: Viscosity

One of the basic components used in most automatic or semi-automatic conformal coating processes is compressed air.  Pressurized air moves the liquid coating from the tank, through the hoses and the valves onto the PCB.  Since the pressurized air makes direct contact with the conformal coating, there are critical properties that must be taken into consideration, especially with moisture sensitive materials. What critical factors are important when working with UV40, UV500, 1A20 or any RTV Silicone from HumiSeal? 

Hello Again!  The last time we discussed bubbles in conformal coating, I wrote how to resolve process related root causes.  There are other simple ways to reduce the amount of bubbles:

• by varying the types of solvents used in a product
• by using a product that contains a surface tension modifier, hence increasing the rate at which bubbles burst.

If you recall, most of the bubbles are basically solvent or air entrapped in the coating.  As you might expect, the air and solvent try to find their way up through the liquid to escape.  The problem is that the surface dries first, creating a thin skin that prevents those bubbles from escaping.  Therefore, the solution is to eliminate the bubbles in the coating prior to the skin formation.   In other words, use a solvent set and other surface tension reducing chemistries to accelerate elimination of bubbles.

"Have you ever experienced air entrapment in your conformal coating?  We would like to offer some assistance to help you to get rid of those exasperating bubbles in the conformal coating process.

Contrary to what most people think bubbles are not material related, bubbles are mostly caused by process related issues.  Yes, it is true that the conformal coating contents would influence in having more or less bubbles.  Solvents will definitively generate bubbles if the process is not properly set but that is not all!  You have to think about  several other factors that could negatively affect the result of your coating application in regards of bubbles.

So, we will talk about not one, but three clever techniques to reduce and/or get rid of the bubbles.