- a tutorial or summary about the basics of ESD protection giving a guide to the methods involved in ESD protection including the ANSI ESD S20.20 standard.
Today electronics equipment reliability levels must be very high to meet the expectations of the market, but at the same time the small size of the components means that they are very sensitive to ESD and they must be treated as Static Sensitive Devices, SSDs. This means that it is essential to protect electronics equipment from the effects of ESD.
It is essential to apply ESD protection to all stages of the life of equipment from the inception of the design, through the production and testing of the electronics equipment, to its final installation and use.
There are many ways in which ESD protection can be applied to electronics circuits and assemblies, as well as to the areas in which they are build, stored and tested. ESD protection is therefore a key element of any electronics organisation. Without sufficient ESD protection measures, not only will equipment show a poor yield in production, but will also exhibit a poor reliability when in service as a result of the latent failures that ESD can cause.
There are many ways in which ESD protection can be implemented. These can broadly be grouped into the following main areas:
- ESD protection at circuit and assembly design: In order that electronics circuits can survive electrostatic discharges encounter in normal use, it is essential that protection is built in to the circuitry. This is normally important on any connections to the outside world.
It is also necessary that sub-assemblies and boards have some measure of ESD protection so that when they are handled, the boards or sub-assemblies have some level of ESD protection.
- Build and test equipment in an EPA: When building electronics equipment, it is necessary that the components, and subassemblies are all handled in a way that prevents them from being exposed to ESD. Often companies these days treat all components as static sensitive devices. The level of ESD protection required in an environment is normally achieved by using what is termed an EPA or ESD protected area. Within an EPA strict controls are employed to ensure that ESD dissipated and that the environment provides protection for any electronics components and assemblies. The use of an EPA or ESD protected area is now standard in any electronics production facility these days.
- Store components in an ESD controlled area: It is not only necessary to ensure that electronics assemblies are built within an environment in which ESD protection is paramount. It is also necessary to ensure that all components are stored and transported within an environment in which ESD protection is implemented. Similarly the ESD protection must also be applied to any sub-assemblies that are stored.
- Introduce an ESD control process: While the installation of equipment and physically generating a static dissipative environment is the first step in creating an ESD protected area, it is also necessary to introduce the right processes and provide training. Only when the personnel using the area known and understand way in which to handle components, assembles and equipment to prevent damage from ESD, will the area work. ESD training and ESD processes are the key to this, as it is absolutely imperative that people know, understand and follow the right processes.
ESD protection strategies
The basis of any ESD protection strategy is to ground or bring all elements in the ESD protected area to the same potential. In this way there is no potential difference between any items that might cause a current to flow. Everything in the ESD protected area must be included and this includes tools, ESD mats and ESD surfaces as well as the electronics assemblies themselves and components. Lastly the humans working on boards must also be included.
When introducing ESD protection measures and strategies, it is necessary to determine exactly what is needed. Some ESD protection measures may be not be cost effective, while others may be essential. When looking at ESD protection measures, it is very easy to take the attitude that all measures must be undertaken to be "on the safe side". However this approach costs money, and it is necessary to take a serious look at the ESD protection measures that will be effective and provide a return for the money invested.
It is not always easy to determine exactly which ESD protection measures should be adopted. It can take many months to prove a process and even longer for figures to be obtained from the field to determine the long-term reliability. Even then it is difficult to attribute failures and low yields to particular areas of a process, and to a particular ESD protection measure that may need to be adopted.
Despite the difficulties, it is necessary to ensure that all figures and metrics are assessed before and after a strategy or new equipment is introduced. By adopting this figures will be available, and it will be possible to better see if there is a problem with the process and possibly with the ESD protection measures that may be in place.
ANSI ESD S20.20 standard
In order to provide standards and assistance to the electronics industry regarding ESD, an organisation known as the Electrostatic Discharge Association, ESDA (www.esda.org) was set up in 1982. A voluntary organisation it has developed various standards and handbooks relating to ESD and ESD practice.
The ESDA has developed the S20.20 standard which is also supported by ANSI and known as the ANSI ESD S20.20 standard. It covers the requirements for designing, establishing, implementing, and maintaining an ESD control program. As a result the ANSI ESD S20.20 standard is often the first stop for ESD information.
Although some of the ESD precautions may seem to be rather extreme, electronic development and manufacturing companies take ESD control very seriously in view of the damage that can be caused. Investment into equipment such as ESD wrist straps, ESD workbenches, ESD flooring,, ESD bags and the like pays dividends in terms of lower fault finding costs during the manufacturing cycle, and also lower warranty repair costs. This does not take into consideration any benefits to be gained from maintaining equipment that gives long and reliable service to customers. Accordingly investment into ESD control is deemed to be a good investment.
By Ian Poole
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