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EMI shielding films and EMC play an important role in the signal integrity of electronic devices. With the increasing problem of electromagnetic interference, the importance of EMI shielding film is becoming more and more prominent. Therefore, the study of EMI shielding film is of great significance in improving the electromagnetic compatibility of electronic equipment and ensuring its regular operation. In this article, we have discussed the basic concept, working principle, types and applications of EMI shielding film. Let's see them together!

What is EMI Shielding Film?

Before discussing EMI shielding films, we first need to understand the basic concepts of EMI (electromagnetic interference) and EMC (electromagnetic compatibility).

EMI shielding film is a special film that can effectively shield electromagnetic interference and improves EMC.

Working Principle of EMI Shielding Film

EMI shielding film blocks electromagnetic fields through its special shielding mechanism, which mainly depends on the conductivity and permeability of the shielding material. A material with good conductivity can form a continuous conductive layer, effectively preventing the penetration of electromagnetic waves. A material with high permeability can guide magnetic field lines around the shielding layer, thereby reducing electromagnetic interference.

In addition, at different frequencies, the shielding effect of the shielding film will be different. EMI in some frequency ranges may be more difficult to block, so more efficient shielding materials and designs are needed. Then, let’s look at its materials!

Types and Materials of EMI Shielding Film

According to the differences in structure, application, and performance, EMI shielding films can be divided into many types. There are the types by material:

In recent years, with the progress of materials science, some new or special EMI shielding materials and technologies have also been developed, like nanocomposites and multilayer structures.

EMI Shielding Effectiveness

The shielding capacity of EMI shielding films depends on multiple technical parameters. These parameters will directly affect the ability of the shielding film to shield, reflect or absorb electromagnetic interference (EMI). Whether applied to flexible circuit boards (Flex PCBs), rigid boards, or electronic enclosures, understanding these key factors is crucial for choosing the appropriate EMI protection scheme. The following lists some factors that affect the shielding effect of the shielding film:

1. Electrical conductivity. A good electronic shielding layer needs to have a low surface resistance in order to effectively direct or reflect electromagnetic energy. Commonly used materials widely applied in various high-performance EMI shielding films include copper, nickel, silver coatings, etc. For transparent EMI shielding film, metal mesh or conductive oxide is used to balance electrical conductivity and light transmittance.

2. Film thickness. In low-frequency band applications, the thicker the film, the better its shielding effect is usually. But in EMI shielding film for FPC, the thick film may limit the bending performance and increase the mechanical stress. Therefore, in flexible applications, a balance needs to be struck between electromagnetic shielding performance and processability.

3. Coverage integrity and bonding performance. The effect of PCB shielding also depends on the uniform covering and reliable bonding of the film layer. Local detachment or poor adhesion can cause electromagnetic leakage. A good EMI shielding film manufacturer can ensure consistent adhesion performance of its products.

4. Different electromagnetic interference sources (such as radio frequency, switching power supply, Wi-Fi) operate in different frequency bands. The choice of EMI shielding film should take into account its shielding effectiveness over the target band (shielding effectiveness).

Applications of EMI Shielding Film

EMI shielding films are widely used in various fields of electronic equipment, such as communications, computers, consumer electronics and so on. Through specific application cases, we can more intuitively understand the role and effect of EMI shielding film.

In smartphones, EMI shielding films are used to protect camera modules from interference from RF circuits.

In automotive electronics, it is used to protect in-car entertainment systems from interference from engines and other electronic devices.

Why is EMI Shielding Film Applied to Flex PCBs and Rigid-flex PCBs?

With the continuous development of electronic equipment, flex PCBs (FPCs) and rigid-flex PCBs (Rigid-flex PCBs) are widely used because of their excellent flexibility, reliability and integration. However, these types of PCBs face a more serious electromagnetic interference problem. Therefore, the application of EMI shielding film is highly important in the process of flex/rigid-flex PCB manufacturing.

PCBasic's flex PCB and rigid-flex PCB can also attach EMI shielding film to you according to your choice.

How to Choose the Right EMI Shielding Film?

When choosing the appropriate EMI shielding film, a multi-dimensional evaluation should be conducted based on specific application scenarios. The following are several suggestions listed for reference:

1. Check the frequency of the interference source. If the interference source comes from RF modules, high-speed processors or wireless communication chips, electromagnetic shielding films with good attenuation capabilities in the GHz frequency band are required. For low-frequency power supply interference, materials with high magnetic permeability can be given priority.

2. Consider the type of substrate and the flexibility requirements. For flexible circuit boards or rigid-flex PCBs, FPC-specific EMI shielding films that do not develop cracks during bending or hot pressing should be selected.

3. Consider the thickness and heat dissipation requirements. In space-compact products, thin EMI shielding films with a thickness of ≤20μm are preferred. For applications that require both heat dissipation and shielding functions, composite copper foil and aluminum foil structures can be adopted to achieve the integration of heat conduction and EMI protection.

4. Consider installation method. Some EMI shielding films support hot-pressing lamination, while others use self-adhesive backing. This requires a choice based on factors such as the level of automation in the product's production process and whether rework is needed.

5. Consider environmental reliability requirements. If the product is applied in harsh environments such as automobiles, industry, and medical care, in addition to shielding performance, EMI protection materials also need to have properties such as moisture and heat resistance and wear resistance. At this point, EMI shielding film manufacturers with long-term reliability verification should be given priority.

EMI Shielding Film vs. EMI Coating/Tape

In electronic product design, engineers often face a choice: whether to use EMI shielding film, EMI coating or tape? The three schemes each have their own advantages and disadvantages, and the applicable conditions and processing methods are also different. Please refer to the table below:

Conclusion

EMI shielding film protects the circuit from electromagnetic interference by forming a continuous conductive layer in the electronic device to weaken the electromagnetic field. And with the continuous development of electronic equipment, the application field of EMI shielding film is also expanding.

For EMI protection of high-density and high-speed flexible circuit boards (FPCs) or complex circuit boards, it is recommended to use metal film type or transparent EMI shielding films. If used in non-critical positions such as casings and covers, EMI coatings can serve as a low-cost solution. If it is only used for temporary protection, testing or repair, EMI tape offers a fast and easy way. In any case, when making a final decision, it is recommended to communicate with an experienced EMI shielding film manufacturer to obtain the best solution suitable for the specific project.

About PCBasic

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