Conformal Coating and Why Is It Used During SMT
In a world of increasingly miniaturized electronics, there are more and more opportunities for them to get exposed to harsh environments. This is especially true of mission critical, IPC class 3 devices that must be reliable even under extreme conditions. Conformal coating is a process that provides additional insulation and protection to these sensitive components.
Conformal coating is a liquid substance that, when applied to a circuit board, will form a protective layer that prevents oxidation, corrosion, and other damage. It is available in a wide range of thicknesses and textures, and can be applied to circuit boards in a variety of ways, including dipping, brushing, spraying, and machine dispensing.
Depending on the type of circuit board, the environment to which it will be subjected, and its sensitivity, the manufacturer may choose to coat every surface or just select areas. In addition to providing extra durability and protection, a conformal coating can provide a number of other benefits for the device, such as increasing conductor spacing, resisting moisture absorption, and reducing EMI.
To achieve the desired results from a conformal coating, it is important to follow the instructions provided by the manufacturer. This typically involves allowing the coated smt circuit board to dry and cure in a controlled environment for a specified amount of time. Once the coating is cured, the circuit board can be inspected to ensure that the coating has fully bonded to the substrate. The inspection should also include looking for signs of bubbles, pinholes, or insufficient coverage.
What Is Conformal Coating and Why Is It Used During SMT?
Before conformal coating is applied to a PCB, it must be clean and free of contaminants such as greases and oils. Contaminants that remain on the substrate can cause de-wetting, in which case the coating material will not adhere to the board. This can result in the development of orange peel, a texture that resembles the skin of an orange [1].
One of the main advantages of the solder mask is its protective properties. It acts as a barrier against environmental contaminants such as moisture, dust, and chemicals, which can corrode the copper traces and lead to circuit failure. By providing this protective layer, the solder mask extends the lifespan of the PCB and enhances the overall durability of the electronic device. This is particularly important in applications where reliability is critical, such as in medical devices, aerospace, and automotive electronics.
To determine if the conformal coating on a PCB is properly bonded, it is necessary to measure the thickness of the coating using an eddy current tester. This non-destructive test involves placing a probe directly against the surface of the coating, and the results are nearly instantaneous. The measured data can then be compared with the standard deviation to evaluate the uniformity of the coating. To avoid inaccurate measurements, it is important to place the probe exactly where it is needed on the PCB. Otherwise, the probe will be measuring the thickness of the air between it and the circuit board, rather than the conformal coating. This can lead to unreliable readings.
