Application of Conformal Coatings

Conformal coatings are very thin layers of material designed to protect the surface of a printed circuit board. These layers are applied onto the circuit board or the substrate and act as a protective coating from harsh elements. Conformal coating is used when the finished product containing the printed circuit board would be exposed to a harsh environment. These environments may include, heat, chemicals, moisture or any environment that could damage the mechanics of a printed circuit or the substrate.

This article will discuss the various types of applications of conformal coatings.

First application is the Dipping Process: this can be done typically by automated equipment or manual application. PCBs are typically hung by an arm and then lowered in a dip tank containing the coating with an immersion rate determined by the population density of the PCB to be dipped. Some advantages of this process is coating penetration under components, coating thickness is assured, can be a fast process time, and this process has a low skill process in application. Some disadvantages of dip coating is thin tip coverage, inconsistent coating thickness, and rather intensive masking is required.

Spray Coating either from an aerosol can or spray gun application is the second most widely used and accepted application of liquid conformal coatings. In this process the material is diluted and sprayed with multiple passes each at a 45 degree angle with multiple coats to achieve desired thickness required. Advantages for spray coating are high volume capable of 1000s of boards per week, reduced masking in comparison to the dip method, better tip and edge coverage, along with a more uniform thickness. Suitable for all conformal coatings. Some disadvantages is multiple passes are needed to achieve desired thickness and there is less penetration of coating under components in comparison to “dipping”

Brush Coating application is commonly used with a low volume production run. During this process it is important to keep the brush loaded with coating and let it flow, do not paint the assembly. Some advantages to this process is the extremely low cost, well suited for low volume applications as well as for repair and rework of an assembly. Disadvantages are it can be slow on labor intensive on large board which also makes for a questionable finish for the assembly.

Selective Spray coating application is very common amongst automotive and other high volume application in which board design and layout does not change much of long periods of time. Fro this application selective spay maximizes throughput by minimizing the amount of masking as well as providing and highly controlled process creating precise repeatability. However there are some disadvantages to this process, boards may still require masking, it does require a skilled operator to program and operate this machine. Programming is time consuming as well: In addition to the high cost of the spray machines.