No matter how perfect the design of your microwave is, penetration of electromagnetic radiations can hardly be prevented. The electromagnetic energy flows into the electrical devices, disrupting the performances of the source circuits and nearby circuits and systems. To control such EMI issues, certain regulations have been framed and complying with them is essential. The manufacturers of electrical appliances and devices need to maintain the EMI emissions standards norms but at the same time, they need to improve the immunity too. This can be done in two ways — board level shielding, which covers the printed circuit board (PCB) and gasketing, which places the device or system in a shielded enclosure.
Board Level Shielding:
This is a cost-efficient can-type shield, which is available in different sizes, shapes and heights. Board-level shielding or BLS is installed in a fully automated fashion through a surface mount technology process. Being a five-sided can, it eliminates the EMI radiation from moving in and out of the PCB. BLS is widely used in the industry because the cans offer very high levels of shielding effectiveness. The shield allows only the standard electromagnetic emission between the source and a receptor. These are manufactured as per the requirement to achieve efficiency. Here are some of the features you need to keep in mind while customizing a BLS for your device.
Performance of the shield will always get affected when it is in the near-field of the source. The field configuration, position of the source, its frequency and distributed inductances and capacitances impact the shielding activities. So, you need to take into account these factors along with the effect of mutual coupling between elements. Proper design of the printed circuit board mounting area is significant for the effectiveness of BLS. The designers need to take into consideration the number and the spacing of vias, interlayer traces, pads and holes to control the noises that escape through these paths affecting the effectiveness of the BLS. The higher frequencies and shorter wavelengths couples with near-field effect minimizing the strength of the shield.
Resonance is yet another issue that should be kept in mind while designing and manufacturing BLS. The self-resonance feature of various structures creates obstacle. Even weak coupling at these extremely high frequencies make strong oscillations, affecting the functionalities of the shield.
Thermal management is essential because when devices move fast they generate more heat. Thermal pads and heat sink should be installed for managing the heat thus produced.
Seam management is unavoidable if you want to make the EMI shielding one hundred percent successful. Gasket takes this responsibility to cut off the leakage from the enclosure design. Materials, contact pressure, surface area — these three determine the effectiveness of the shield. Gasket merges the rigid surfaces together to set continuity between metal pieces, thus minimizing the radiation effect. This type of shielding can be made of different types of materials. The common ones are as follows:
The beryllium copper gasket is ideal for doors and panels. It is flexible and performs well to shield EM radiation.
Metalized fabric gaskets, on the other hand, are made of conductive fabric material over foam. This can create a strong enclosure.
Attenuating the amount of electromagnetic energy is the ultimate intention of these two shielding methodologies. It is essential to ensure that the radiation complies with the standard regulatory guidelines, which at times, is challenging. In order to get the benefits of board level shielding, following the guidelines of designing and manufacturing is necessary, whereas for gasketing you need to choose the right type of material to curb the EM leakages. The key to successful shielding is to understand the requirements of a particular application and then design it accordingly.