Electromagnetic interference or EMI, as well as radio frequency interference or RFI, cause noise or a disturbance which may impair the functioning of an electronic device or a communication network. Hence, it is essential to mitigate EMI from interfering or clashing with signals from a device to maintain normal functioning and prevent damage. Various methods are implemented to suppress or control EMI, such as shielding cans, EMI shields, EMI absorber sheets and more. While EMI shields are a great option to suppress EMI even at the PCB level, EMI absorber sheets are also gaining traction. Both these may seem the same, but they are slightly different conceptually. This post discusses how EMI absorber sheets can be used to reduce noise in electronic devices, their application at the board level, and a comparative account with board-level shields.
What Are EMI Absorber Sheets?
These are thin, flexible, and non-conductive sheets made of rubber or polymer and loaded with specific filler particles or soft metal flakes. Absorber sheets can be directly pasted on circuits and traces safely without damaging the IC pins. They can be cut out in various shapes and thicknesses around 1mm. EMI absorber sheets help eliminate noise across a broad frequency range from 10MHz to 60 GHz. Electronic devices nowadays emit large amounts of electromagnetic waves because of complex designs, high-speed transmission requirements, and so on. EMI absorber sheets absorb the electromagnetic field generated by these devices.
Benefits of Using EMI Absorber Sheets
Here are some beneficial features of using EMI absorber sheets at device and board levels.
- They have an adhesive film on one side, making them easy to use. EMI absorbers are supplied in the form of a sheet or roll and can be easily cut with a pair of scissors.
- By reducing EMI or RFI emissions, they help improve the performance and efficiency of the device.
- They are safe and reduce the risk of shorting even if applied on circuits.
- While most are UL certified and RoHS compliant, it is essential to check the UL rating when investing in EMI absorbers and ensure they meet your application requirements. For instance, UL94V-0 are flame retardant EMI absorbers, which you can buy if your application requires them.
- With the increasing miniaturization of electronic devices, EMI absorbers come handy as they can be made in very small sizes and customizable shapes.
- They have three compressed layers - insulation, pressure-sensitive adhesive, and EMI absorption, offering flexibility, EMI shielding, and easy application.
- These sheets shield EMI and improve signal integrity in electronic circuits, especially in high-frequency and high-speed applications.
- At the board level, sensitive electronic components are protected from internal and external electromagnetic interference, which helps extend their operational life.
- The use of these sheets in electronic devices and PCBs helps electronics manufacturers meet industry standards and comply with FCC and CE regulations for control of electromagnetic emissions.
- EMI absorber sheets also help dissipate heat, which prevents overheating and subsequent damage of components.
Applications of EMI Absorber Sheets
EMI absorber sheets are best suited for near-field applications around electronic devices and assemblies. Here are some common application areas of EMI absorber sheets.
- Mobile phones: SAR or specific absorption rate is the measurement of mobile phone emissions absorbed into human tissue. This rate of absorption must be reduced to enhance the safety of mobile phone usage. EMI absorber sheets help achieve a low SAR value as they suppress EMI at component level. This same factor also applies to wearables and other handheld devices.
- Laptops and computers: Using these absorber sheets in laptops and computers helps decrease the inter-device and inter-component EMI.
- Digital cameras: Camera module components also need to be shielded from EMI. Absorber sheets are a convenient option for small components used in digital cameras.
- Wireless communication modules: They are used in wireless chargers, Wi-Fi modules, and Bluetooth devices.
- Military and aerospace equipment: They are used in avionics to prevent interference between various systems such as navigation, control, communication, etc. These absorber sheets are also widely used in electronic warfare systems.
Key Considerations When Choosing EMI Absorber Sheets
Here are some factors to consider when choosing EMI absorber sheets.
- Frequency range of operation: EMI absorber sheets are suitable for a very wide frequency range; however, the absorption rates vary with the frequency range. Hence, it is important to identify the right frequency range for your device.
- Material properties: You need to decide on the material, such as rubber, plastic, based on its physical and chemical properties and the compatibility with your application requirements. You also need to determine the thickness and level of flexibility you require, which would depend on the material properties. Hence, selecting the right material is crucial.
- Adhesive backing: An acrylic pressure-sensitive adhesive film works for EMI absorption sheets. Ensure it has a removable liner which makes the sheet’s application easy.
- Environmental factors: Operating temperature, exposure to heat, and many other environmental parameters related to your application must be considered when deciding on EMI absorption sheets.
- Size and shape requirements: You can opt for customized EMI shields or absorption sheets to get the exact size, shape, and dimensions that match your board or device.
EMI Absorber Sheets Vs. Board Level Shields
PCB EMI shields are typically designed to mitigate board level EMI, while EMI absorber sheets can also be used at the device level to control external EMI. PCB shields have one conductive side, while the other side is non-conductive. On the other hand, EMI absorber sheets are totally non-conductive. PCB EMI shields can be cut out in extremely thin sizes below 1mm, while EMI absorber sheets are slightly thicker.
Achieving immunity against EMI is crucial for any electronic or electromechanical equipment. The effectiveness of these devices increases if the shields or absorbers are fitted at the board level. Any effective form of shielding is necessary because of the densely mounted components and complex designs, limited space available in small devices, and other such factors. While most devices nowadays are designed to be EMC compatible, EMI suppression or filtration is an essential step. While non-conductive EMI absorber sheets are fairly effective in mitigating EMI, consider plasticized EMI shields that have one conductive side. XGR Technologies offers SnapShot® EMI shields made from a thin polyetherimide film on the interior and conductive tin on the exterior surfaces. These are flexible and lightweight shields that help reduce electromagnetic inference. If you need further information on these EMI shields, you can contact the team at XGR Technologies via phone or email.
