Research on the Shielding Effect of Conformal Coating Materials on Electromagnetic Waves of Different Frequencies

With the rapid development of electronic technology, the application of electronic devices has become increasingly widespread, and their working environments have also become more and more complex. During the operation of electronic devices, problems such as electromagnetic interference (EMI) and electromagnetic radiation (EMR) have gradually become prominent. Electromagnetic interference will not only affect the normal operation of electronic devices, leading to performance degradation or even failure, but may also pose potential hazards to human health. Electromagnetic radiation may also interfere with other surrounding electronic devices, affecting the stability and reliability of the entire system.

Conformal coating, as a material that can form a uniform, continuous, and dense protective film on the surface of electronic devices, plays an important role in the protection of electronic devices. In addition to basic protective functions such as moisture resistance, mold resistance, and salt spray resistance, some conformal coatings also have good electromagnetic wave shielding performance. By coating conformal coatings on the surface of electronic devices, electromagnetic interference and radiation can be effectively reduced, and the electromagnetic compatibility (EMC) of electronic devices can be improved.

Electromagnetic waves of different frequencies have different characteristics, and their attenuation and shielding mechanisms during propagation also vary. Therefore, studying the shielding effect of conformal coating materials on electromagnetic waves of different frequencies is of great significance for the rational selection and application of conformal coatings and improving the electromagnetic protection performance of electronic devices.

Basic Concepts and Classification of Conformal Coatings

(I) Definition of Conformal Coatings

Conformal coating is a special type of coating that can form a thin and uniform protective film on the surface of the coated object (such as printed circuit boards, electronic components, etc.). This protective film can closely adhere to the shape of the object surface. Whether the object surface is flat, curved, or has complex concave and convex structures, the conformal coating can form a continuous coating, thus providing comprehensive protection for the coated object.

(II) Classification of Conformal Coatings

Organic Conformal Coatings

Acrylate-based: It has good transparency, weather resistance, and chemical stability, and has a good protective effect on electronic components. At the same time, acrylate-based conformal coatings also have good flexibility and can adapt to a certain degree of thermal expansion and contraction.
Epoxy resin-based: Epoxy resin conformal coatings have excellent adhesion, chemical corrosion resistance, and mechanical properties. It can form a hard protective film on the surface of electronic devices, effectively resisting the erosion of the external environment.
Silicone-based: Silicone-based conformal coatings have the characteristics of high temperature resistance, low temperature resistance, and strong weather resistance. In a high-temperature environment, the silicone coating can maintain good performance and is not prone to aging and deterioration.

Inorganic Conformal Coatings

Ceramic Coatings: Ceramic conformal coatings have the advantages of high hardness, high temperature resistance, and wear resistance. It can form a dense ceramic film on the surface of electronic devices, providing good physical and chemical protection.
Metal Oxide Coatings: Some metal oxide coatings, such as zinc oxide, titanium dioxide, etc., have a certain electromagnetic wave shielding performance. These coatings can be coated on the surface of electronic devices through special preparation processes to play the role of shielding electromagnetic waves.

Principle of Electromagnetic Wave Shielding

(I) Reflection of Electromagnetic Waves

When electromagnetic waves encounter a shielding material, a part of the electromagnetic waves will be reflected on the surface of the material. The degree of reflection depends on the impedance difference between the shielding material and the surrounding medium. If the impedance of the shielding material is significantly different from that of the surrounding medium, the reflection of electromagnetic waves on the surface of the material will be relatively strong.

(II) Absorption of Electromagnetic Waves

In addition to reflection, a part of the electromagnetic waves will enter the shielding material. Inside the shielding material, the electromagnetic waves will interact with the electrons, atoms, etc. in the material, causing the energy of the electromagnetic waves to be absorbed and converted into other forms of energy such as heat energy. The absorption ability of the shielding material to electromagnetic waves is related to the physical properties of the material, such as electrical conductivity and magnetic permeability.

(III) Multiple Reflections and Scatterings of Electromagnetic Waves

Inside the shielding material, electromagnetic waves may also undergo multiple reflections and scatterings. These multiple reflections and scatterings will further increase the propagation path of electromagnetic waves inside the material, thus increasing the energy loss of electromagnetic waves and improving the shielding effect.

Experimental Part

(I) Experimental Materials

Three common conformal coating materials were selected: acrylate-based conformal coating, epoxy resin-based conformal coating, and silicone-based conformal coating.
Printed circuit boards (PCBs) with a size of 100mm×100mm were prepared as the test substrates.

(II) Experimental Equipment

A vector network analyzer (VNA) was used to measure the shielding effect of the conformal coating on electromagnetic waves of different frequencies. The vector network analyzer can accurately measure the reflection and transmission coefficients of electromagnetic waves during the transmission process.
A shielding box was equipped to provide a relatively shielded test environment and reduce the interference of external electromagnetic waves.

(III) Experimental Steps

Clean the printed circuit board to remove oil stains and impurities on the surface.
Coat different types of conformal coatings on the printed circuit board respectively, and control the coating thickness to be 0.1mm, 0.2mm, and 0.3mm.
Put the printed circuit board coated with the conformal coating into an oven and carry out the curing treatment according to the curing process of the coating.
Put the cured printed circuit board into the shielding box, and use the vector network analyzer to measure its electromagnetic wave shielding effectiveness (SE) in the frequency range of 100MHz to 10GHz.

Experimental Results and Analysis

(I) Shielding Effectiveness of Conformal Coatings at Different Frequencies

Low Frequency Band (100MHz – 1GHz)

The shielding effectiveness of acrylate-based conformal coatings in the low frequency band is relatively low, approximately between 10dB and 20dB. This is because acrylate-based coatings have a low electrical conductivity and weak reflection and absorption capabilities for low-frequency electromagnetic waves.
The shielding effectiveness of epoxy resin-based conformal coatings in the low frequency band is slightly higher than that of acrylate-based coatings, about 15dB to 25dB. The molecular structure of epoxy resin is relatively dense, which can block the propagation of low-frequency electromagnetic waves to a certain extent.
The shielding effectiveness of silicone-based conformal coatings in the low frequency band is also not high, generally between 10dB and 20dB. The characteristics of silicone materials limit their shielding effect on electromagnetic waves in the low frequency band.

Medium Frequency Band (1GHz – 5GHz)

As the frequency increases, the shielding effectiveness of acrylate-based conformal coatings increases, reaching 20dB to 30dB. In the medium frequency band, the wavelength of electromagnetic waves is relatively short, making it easier to interact with the coating molecules, thus increasing the absorption and reflection of electromagnetic waves.
The shielding effectiveness of epoxy resin-based conformal coatings in the medium frequency band also increases significantly, about 25dB to 35dB. The cured structure of epoxy resin has a more significant shielding effect on electromagnetic waves in the medium frequency band.
The shielding effectiveness of silicone-based conformal coatings in the medium frequency band increases to 20dB to 30dB. The silicon-oxygen bonds in the molecular structure of silicone materials have a certain absorption and scattering effect on electromagnetic waves in the medium frequency band.

High Frequency Band (5GHz – 10GHz)

The shielding effectiveness of acrylate-based conformal coatings in the high frequency band is further improved, reaching 30dB to 40dB. High-frequency electromagnetic waves have higher energy, making it easier to be absorbed and scattered by the molecules in the acrylate-based coatings.
The shielding effectiveness of epoxy resin-based conformal coatings in the high frequency band is about 35dB to 45dB. Due to the high hardness and dense structure of epoxy resin, it can effectively block the propagation of electromagnetic waves in the high frequency band.
The shielding effectiveness of silicone-based conformal coatings in the high frequency band is 25dB to 35dB. The high temperature resistance and chemical stability of silicone materials are helpful for the shielding of electromagnetic waves in the high frequency band.

(II) Influence of Coating Thickness on Shielding Effectiveness

For acrylate-based conformal coatings, as the coating thickness increases, the shielding effectiveness gradually increases. When the coating thickness increases from 0.1mm to 0.3mm, at a frequency of 10GHz, the shielding effectiveness increases from 30dB to 35dB. This is because a thicker coating can provide more absorption and reflection paths for electromagnetic waves.
Epoxy resin-based conformal coatings also show a similar pattern. When the coating thickness is 0.1mm, the shielding effectiveness at a frequency of 10GHz is 35dB; when the coating thickness increases to 0.3mm, the shielding effectiveness increases to 45dB. A thicker epoxy resin coating can better exert its blocking effect on electromagnetic waves.
The shielding effectiveness of silicone-based conformal coatings also increases with the increase of the coating thickness. At a frequency of 10GHz, the shielding effectiveness is 25dB when the coating thickness is 0.1mm, and it increases to 35dB when the coating thickness is 0.3mm.

Analysis of Factors Affecting the Shielding Effect of Conformal Coatings

(I) Material Composition

The type and content of conductive fillers (such as metal powders, carbon nanotubes, etc.) in the conformal coating have an important impact on the shielding effect. Conformal coatings containing an appropriate amount of conductive fillers can increase the electrical conductivity of the material, thereby enhancing the reflection and absorption capabilities of electromagnetic waves.
The molecular structure and properties of the polymer matrix also affect the shielding effect. For example, polymer matrices with conjugated double bond structures can have a stronger interaction with electromagnetic waves, improving the absorption efficiency of electromagnetic waves.

(II) Coating Thickness

As shown in the experimental results, the increase in coating thickness can improve the shielding effectiveness of the conformal coating. A thicker coating can provide more absorption and reflection paths for electromagnetic waves, increasing the propagation distance of electromagnetic waves inside the coating, thereby improving the shielding effect.

(III) Preparation Process

The preparation process of the conformal coating, such as the coating method (spray coating, brush coating, dip coating, etc.), curing conditions (temperature, time, etc.), will affect the uniformity and density of the coating. A uniform and dense coating can better block the propagation of electromagnetic waves and improve the shielding effect.

Conclusion and Prospect

(I) Conclusion

Different types of conformal coating materials have different shielding effects on electromagnetic waves of different frequencies. In the low frequency band, the shielding effectiveness of conformal coatings is relatively low; as the frequency increases, the shielding effectiveness gradually increases.
The coating thickness has a significant impact on the shielding effectiveness of the conformal coating. Increasing the coating thickness can improve the shielding effect.
Material composition and preparation process are also important factors affecting the shielding effect of conformal coatings. Reasonable selection of material composition and optimization of the preparation process can improve the electromagnetic wave shielding performance of conformal coatings.

(II) Prospect

Future research can further explore new types of conformal coating materials, such as nanocomposites with special structures and properties, to improve their shielding effect on electromagnetic waves of different frequencies.
Conduct in-depth research on the interaction mechanism between the conformal coating and the surface of electronic devices, optimize the coating process, and improve the adhesion and uniformity of the coating, so as to better exert the shielding effect of the conformal coating.
With the development of technologies such as 5G and the Internet of Things, the requirements for the electromagnetic compatibility of electronic devices are getting higher and higher. As an important electromagnetic protection material, conformal coatings will play a more important role in these fields. In the future, special conformal coating products can be developed according to the needs of these emerging technologies to meet the requirements of different application scenarios.

In conclusion, conformal coating materials have broad application prospects in the field of electromagnetic wave shielding. Through continuous research and innovation, it is expected to further improve their shielding performance, providing better protection for the normal operation of electronic devices and the protection of the electromagnetic environment.

For more about research on the shielding effect of conformal coating materials on electromagnetic waves of different frequencies, you can pay a visit to DeepMaterial at https://www.uvcureadhesive.com/ for more info.