Antistatic (ESD) and EMI protection in electronics production

Electronics Technical ArticlesSouth-East European INDUSTRIAL Мarket - issue 3/2021 • 08.10.2021

Unfortunately, electronic systems and devices can be vulnerable to being negatively impacted by electrostatic discharge (ESD) and electromagnetic interference (EMI). The industry has come a long way in understanding how electronic devices are impacted by both, measures manufacturers can take to reduce or prevent them outright, and creating guidelines to regulate acceptable limits of EMI. By implementing the proper ESD and EMI protection solutions, producers can mitigate these phenomena. That will go a long way to improving the quality of goods and products the plant produces, but it will also protect everything contained within, including industrial equipment, electronics, and machinery.

 

ESD protection

Although electrostatic discharge may not look dangerous in theory, it can be exceptionally so, especially for microelectronics and industrial machinery. It happens to be one of the few frequent events that can damage almost any computer or related hardware components. Additionally, discharge events can occur without anyone knowing or feeling anything.

ESD is defined as a static discharge that moves from one conductive surface to another. Preventing it requires a ground that can eliminate static build-up. The ground source may come in the form of a wrist strap, grounding mat or surface or even work environment segment. Tools that can further prevent discharge problems include everything from an antistatic cover or bag to a type of antistatic spray that mitigates discharge potential for a component.

However, avoiding ESD on the manufacturing floor is a little more complicated. Research shows that the average electronics product losses due to ESD can be anywhere between 8 and 33%. In monetary damage, estimates run into the billions of dollars annually.

The first step to ESD protection is to determine where it occurs, affected materials and how a charge flows. It is important to consider that certain materials such as styrofoam, plastics, electronic components and devices, and even the human body are more capable of creating and facilitating an electric discharge.

Circuit design processes are among the main pillars of electrostatic discharge protection. While ineffective design is one of the most common reasons for PCB failure, the right design will guarantee ESD damage doesn´t affect electrical components. Nevertheless, even the best designs are not enough themselves to stop ESD from happening outright and only the right prevention measures within a manufacturing plant can do that.

Manufacturers must implement process guidelines and procedures to eliminate the possibility of ESD, including through the use of special protective equipment. Even something as simple as antistatic gloves can be the difference between hundreds of damaged products or none at all.

Sometimes failures caused as a result of ESD may be minor, meaning they will not necessarily manifest until later in the product´s lifecycle. With some consumer electronics, this issue is merely costly, but the consequences can be severe for more sensitive electronics such as medical implants.

Creating a protected area is the very best approach to ESD prevention – everything within the space, including objects, workbenches, equipment, people and extraneous items, is kept at the same electrical potential. All surfaces should be covered in groundable materials, which have an electrical resistance rating of fewer than 109 ohms. A similar technique bonds any loose items to a ground. A bonded surface such as an antistatic mat covers the floor, so any people in the area remain bonded too.

An ESD control program incorporates not just this kind of setup, but also a process for reviewing and maintaining the environment as a regular operation. The program should require personnel to review an area before beginning their workday, which ensures the adequate maintenance of all conditions. It also includes a policy to assess and replace equipment, tools, and other items that should remain bonded if and when there is a problem.

It is often misunderstood that wearing an ESD coat or suit automatically protects the nearby equipment and electronics. That is totally wrong – the garments must have an electrical bond just like anything else. Proper ESD wear also calls for the use of bonded footwear, or grounded wrist straps to reduce the potential for discharge. Besides, specific garments lose their ESD properties over time, which means they require regular replacement.

Many companies invest a lot into the installation of ESD control products and systems. When installed and maintained properly, they are incredibly useful, but they require regular assessment. Failure to review the systems or check them after installation means that they could be working out of specification. Therefore, a compliance verification plan is necessary to check the equipment and systems periodically, but also to ensure that the proper testing equipment is available and is also in working order.

ESD shielding bags and films can help store, transport or protect sensitive goods. Under the right conditions, they create a secure environment or a Faraday cage. But the shielding is vulnerable to tears, cuts, scratches and more. Companies can also use shielding gear when packaging or shipping goods to customers. Some organizations that want to save money may reuse the same shielding materials or bags, which inadvertently introduces any related goods to an increasing risk. The damaged shielding no longer functions properly as a protective film or cover. The same is true of everything from antistatic gloves to bags and even sprays. This is why manufacturers in the electronics industry should put a proper system in place to review, monitor and replace damaged shielding and similar components.

Another common problem is related to workers using standard household cleaning products on ESD matting, garments, and other bonded goods. Most cleaners include silicone, which spreads out in a thin layer upon the cleaned surface, giving it a fresh and shiny look. The problem is that the thin silicone layer creates insulation, reducing the grounding performance of the material and increasing the potential for static discharge. There are special cleaners designed for use with ESD mats, which is what companies should use on the manufacturing floor.

Last but not least, regardless of how skilled or experienced employees are, everyone should have to take part in regular training and awareness courses. Most operations only require new hires to complete such training, but there should be a continuous program in place, which will also allow experienced workers to stay abreast of any new methods, technologies, and systems that get introduced as operations evolve.


Preventing or reducing EMI

The phenomenon of electromagnetic interference occurs when the operation of an electronic device is disturbed by an electromagnetic (EM) field. It typically occurs when the device is in proximity to an EM field, which disrupts the radio frequency spectrum. EMI is a common issue for electronic components used in various industries, such as military, defence, communication systems, appliances, and aerospace. Sources of EMI are various, both natural and man-made. It can take on multiple characteristics dependent upon its source as well as the nature of whatever mechanism is giving off the interference.

Broadband EMI consists of EMIs that do not occur on single/discrete frequencies, and they take up a large portion of the magnetic spectrum. Common causes of broadband EMIs include arcing or corona discharge from power lines, and it makes up for a large portion of EMI issues in digital data equipment. Examples of this kind of EMI include faulty brushes in motors/generators, arcing in ignition systems, bad fluorescent lamps, defective power lines and sun outages disrupting the signal from a communication satellite. Luckily, these kinds of issues only last for a few minutes. Narrowband EMI conversely is made up of a single carrier source resulting from spurious signals occurring from different kinds of distortion in a transmitter or are generated by a form of an oscillator.

There are various methods available to prevent and reduce interference with electronic devices because it can affect circuits and prevent them from working correctly. Managing electromagnetic interference makes up a large number of different solutions at both the emitter and victim devices. Sometimes, it can be as simple as moving devices, so there is more space between the source and victim or even rotating one device can work. While these can be useful, the better solution includes the proper design of all equipment to minimise emissions and/or making the equipment less vulnerable to external interference. There are three different methods to help reduce EMI – filtering, grounding and shielding.

A direct way to get rid of unwanted signals is through filtering them out and in this case, passive filters work well, and they´re used in most new equipment to minimise EMI. Filtering usually begins with an AC line filter that prevents any bad signals from entering the power supply or powered circuits, and it keeps internal signals from being added to the AC line. The method is commonly applied to cables and connectors on lines into and out of a circuit, and some special connectors can have built-in low-pass filters whose main job is to soften digital waveforms to increase the rise and fall times and reduce harmonic generation.

On the other hand, shielding is the preferred approach to contain radiation or coupling in source or victim devices, and it usually includes encasing the circuit inside a completely sealed enclosure, such as a metallic box. Shielding is of considerable importance as it reflects electromagnetic waves into the enclosure and absorbs waves that aren´t reflected. Very often a small amount of radiation ends up penetrating the shield if it´s not thick enough.
Practically any common metal can be used for shielding (e.g. copper, steel, aluminium).

Grounding is the establishment of an electrically conductive path between an electrical or electronic element of a system and a reference point or plane referenced to ground, and it can refer to an electrical connection made to Earth as well. Among the recommended practices to achieve the best possible ground include: keeping leads away from internal circuits or any other components to ground as short as possible to reduce inductance; using multiple grounding points on a large ground plane for best results; trying to isolate circuits from ground if ground loop voltages can,t be controlled any other way; maintaining separate grounds for analogue and digital circuits (they can be combined later at a single point). Applying any one of these three approaches can help not only reduce EMI but can also ensure that the equipment is less vulnerable to future interference and can assist with reducing emissions.

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