Radio frequency interference (RFI) has existed way before the advent of electronics and digital signals. This is a type of interference that occurs with telephone lines, radios, and the old analog electrical devices used decades ago. This is caused due to the propagation of electrical signals coming from transmitters, phones, and amplifiers on the same frequency to the one you are receiving through a radio station or so. The frequency spectrum for RFI signals ranges from 9kHz to 300GHz. Clashing of these signals causes noise that disturbs the functioning of the circuit in any electrical devices around. Just like EMI or electromagnetic interference which became a household term after the advancements in electronics, RFI occurring due to radio waves can disturb the functioning of a circuit in PCBs. This post discusses the impact of RFI on PCBs, ways to mitigate it, and more.
How RFI Negatively Impacts PCB Circuits
These are some of the effects of RFI on PCB circuits which hampers their functioning and also that of the device.
- Signal attenuation: RFI directly hampers the signal path causing signals to degrade or distort on the way. Poor signal quality results in poor audio or video quality in case of data transfer. In case of telecom, it leads to dropped calls or disrupted communication.
- False triggers and alarms: Interference can activate false responses, especially in case of sensitive devices. These false triggers are usually through alarms and sensors in devices, which hampers the further process such as wrong readings, measurement, and so on. This leads to malfunctioning of the machine or equipment.
- Signal losses: Excess quantities of RF waves can at times completely block a transmission path leading to signal losses and subsequent breakdown in communication and network.
- Noise and crosstalk: This is a very common issue, wherein RF waves interfere with signals from a nearby device which may in the same frequency range and cause noise. This type of interference can lead to cross communication due to mixing of signals.
What Causes RFI?
There are various sources of RFI with increasing number or electronic devices in day-to-day life. This causes overcrowding of RF waves. Increasing number of devices in a network and even multiple components mounted on a PCB can cause clashing of RF signals. If a PCBA does not have proper enclosure, that is a major avenue for RF waves from external sources to enter the circuit. Poorly designed circuit boards with little space amid the layers can trigger RFI. It is crucial for any PCB manufacturer to comply to industry standards in terms of design and EMC regulation. The Title 47 of the Code of Federal Regulations (CFR) or 47CFR has the emission standards for EMC which manufacturers need to follow. These are standardized and regulated by Federal Communications Commission (FCC). Using set standards and intelligent board designs, it is possible to mitigate EMIs. However, using PCB shields is a major aspect in controlling RFI as well as EMI.
Ways to Mitigate RFI from PCBs
Fortunately, there are ways to shield the boards from EMI and RFI. An important aspect is to make the board EMC enabled, which means they are designed to function normally in the presence of electromagnetic waves. Here are some ways to mitigate RFI from circuit boards.
- EMC testing: It is paramount for board manufacturers to design the PCBs such that they can function normally in the presence of electromagnetic waves. Stringent testing for electromagnetic compatibility must be performed.
- Filtering: In this method, the incoming RF waves are suppressed by installing RF filters or using frequency-selective devices. This blocks unwanted signals and allow only the selected or required RF frequencies to pass through. Capacitors are a good filtering device.
- Grounding: Grounding is a common as well as essential technique used for any electrical and electronic circuits to prevent the risk of shorting and so on. In case of PCBs, there is a ground plane located centrally between positive and negative terminals in a circuit. To proper grounding techniques, it is necessary to know the current flow well. Conductive rings should be avoided in these ground planes to prevent RF waves to cause noise.
- Frequency planning: With a gamut of devices and their radiation, in the air, planning specific frequency ranges to devices and systems is a good option for cutting down RFI. This is because most devices use the radio frequency range between 9kHz and 300GHz. However, such planning may involve certain challenges.
- Shielding: This is by far the best option to filter RFI or electromagnetic waves in just any frequency. There are various types of shields, cans, enclosures, and so on which prevent external EMI from interfering with sensitive equipment or systems. The internal RF waves coming from various components are suppressed to prevent noise. In case of PCBs, EMI shields work well. However, they must rightly fit the board shape, thickness, and dimensions, and hence custom shields are the best option.
All said and done, it is necessary to filter or mitigate RFI at all costs to ensure the PCBA and concerned device function normally. As a PCB manufacturer, you may require custom PCB shields to mitigate EMI and RFI. Hence, when partnering with a shields manufacturer, look for someone with a high level of customization capabilities to get the right fitment in terms of thickness, shape, dimensions, and so on. XGR Technologies offers SnapShot EMI shields that meet the US EMC standards and are highly customizable. They are 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 coupling. If you need further information on these EMI shields, you can contact the XGR Technologies team via phone or email.
