EMC Principles for Electronics Product Design
By Engaged Expert Steve Hayes
From research and development to final certification, electromagnetic compatibility (EMC) should be a key focus of electronics product design. In addition to ensuring product safety and wireless coexistence, considering EMC principles in the early stages of a product helps smooth the path to compliance – and prevents the cost and time associated with redesign.
With our experience getting thousands of products successfully through final compliance and certification, we have identified the three most essential elements of EMC on product design – filtering, shielding and earthing/grounding.
The amount of electrical noise a product emits is not important; it needs to be connected to an antenna (i.e. cables, pcb track, etc.) for it to radiate or receive and cause issues. Consequently, all signal lines, especially those connected to the outside world, should be given specific treatment. This means filtering either at the point of source (emissions) or at point of entry (susceptibility). Filters are typically passive components which suppress RF noise, and can be used internally on PCBs or externally on cables.
There are various methods of filtering, which include:
- Capacitor or inductor components
- Small amount of capacitance from signal to ground
- Ferrite beads acting as an inductor on whole signal/cables bundles
Filters can be a simple retro-fit installation, but can be expensive if required to be added to a significant production run. Different materials have different properties with respect to frequency, and manufacturer's literature helps you to select the most effective material for the frequency range. Design improvements during the product and pre-testing stage can reduce reliance on filters.
"With our experience getting thousands of products successfully though final compliance and certification, we have identified the three most essential elements of EMC on product design: filtering, shielding, and earthing/grounding." Steve Hayes
Depending on a product’s function, some devices produce unwanted electrical noise. The best way to prevent this noise from spreading to other, more effective radiators (such as cables) is to create a containment strategy.
A screening can (which is only solder fixed at each corner) may not be sufficient, and having a weld along the full length of the folds is critical to ensure metal-to-metal contact so a slot antenna is not inadvertently produced.
If shielding is used, then ensuring a complete Faraday Cage is important. Holes for cabling, monitors and ventilation will affect the integrity of the shield, so EMC honeycomb mesh and screened cables or metal to metal contact will help with 360 degree termination of enclosures for shielding. Thicker shield material will attenuate better by either reflection and/or absorption.
Earthing/Grounding is the treatment of ‘potential differences.’ For example, in the event of an electrostatic discharge (ESD), a voltage exposed to a product is simply trying to find the quickest route to the ground. If an ESD event is applied to a cable, and that same cable is directly connected to a PCB, the energy will travel along the cable and cause the ground plane on the PCB to jump up to the potential of the ESD level, potentially causing damage or malfunction. If that same cable was terminated on the board where the earth/ground connects to the mains entry point, the issue would be resolved.
Earthing/grounding can be achieved through various methods which can include:
- Flexible wires
- Flexible braid
- Metal plating
Flexible ground straps can be more usable, but this comes at the expense of effectiveness.
“By testing during the design phase, most of the potential issues and failures found in compliance testing can be mitigated.”
Applying Filtering, Shielding and Earthing/Grounding to Mitigate Test Failure
The EMC principles of filtering, shielding and earthing/grounding are considered during electronics product design. Failure during compliance testing can result in lengthy delays to market, as products are redesigned to meet required standards.
Pre-certification and pre-compliance testing is an effective tool to test EMC emissions and susceptibility. By testing during the design phase, most of the potential issues and failures found in compliance testing can be mitigated. It gives product designers and EMC engineers the necessary data required to improve product performance and speed up the design process.
Through our comprehensive Early Stage Qualification (ESQ) pre-certification testing services, we help ensure that your products are designed with compliance in mind, and can get to market on time and on budget.
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