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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

The application of the conformal coating in a uniform and consistent coverage is a key challenge that defines the reliability of the finished product.

A thin coating will provide inadequate protection against corrosion or insulation between conductors. Conversely, if the conformal coating is too thick, it will increase the risk of forming other types of coating defects such as bubbles, insufficient curing, and potential cracking during thermal shock cycles.

Besides the verification of the process parameters such as coating viscosity and the application method is correctly setup, the amount of conformal coating material applied on the printed circuit boards can be measured before curing. For this, wet film conformal coating thickness gauges are used. This method ensures quality control while the coating material is still wet.

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? 

During your selection of conformal coating you ran in to a specification that you have seen before but not fully understood, MIL-I-46058C.   Conformal coating choices are vast, but with so many available, how does a user pick the correct one? Are there minimum standards that define what a conformal coating is supposed to do? Thankfully, yes there are. This article will focus on one such standard: MIL-I-46058C.

The official title for the specification is MIL-I-46058C, Insulating Compound (For Coating Printed Circuit Assemblies). The standard serves as a material standard, used to evaluate and document that a particular coating meets a list of specific performance attributes (more on those later). The MIL-I-46058C was developed to define a uniform set of test methods and performance requirements for conformal coatings and gives users confidence that the material they select will perform.