ESD – a serious matter along the entire supply chain

Most people will have experienced ESD in their daily lives, such as touching a metal doorknob after walking across a carpet, or the static electricity felt after drying clothes in a tumble dryer. Lightning is a good example of a large scale ESD event.

Most ESD occurs without being significant enough to be seen or heard, but it is often still large enough to cause the failure of sensitive solid state electronic components. For this reason, ESD prevention and control has been a hot topic at electronics manufacturers for a number of years. Assembly personnel are instructed to use devices such as anti-static wrist bands and grounding mats as these provide the path to ground for any unwanted static energies and avoid component damage or destruction. Most electronic equipment manufacturers or service providers will have an electrostatic protected area (EPA).

This is vital because most ESD damage is caused unwittingly. Sometimes, electronic components or modules that are not destroyed totally are left damaged or impaired. Unfortunately, this type of damage cannot be identified through standard quality tests, and could surface after the component is installed in its host equipment or after some time while in use.

Of course, controlling ESD at the manufacturer has been an established practice for many years. But what about the remainder of the supply chain? After all, the growing market share commanded by distributors prompts the question – is ESD controlled here too? Customers demand reliable, high quality products whether they are purchased directly from the manufacturer or via a distributor.

With this in mind, buyers should ask their distributor if they are certified, namely does the company have a DIN EN 61340-5-1 certified ESD zone and ESD management at its distribution location? Only this will ensure the highest standards in terms of storage and handling of electrostatic sensitive devices, and guarantee the quality of products shipped. Ask if the area has been tested by a leading technical service provider to ensure it is 100% compliant to ESD requirements.

Many of the latest industrial and consumer designs utilise advanced electronic components that are particularly sensitive to ESD and need special storage and handling procedures at all stages of the supply chain. Clearly, the deployment of an EPA at distributor level will help ensure the reliability of end products and systems in which the components are used. This is essential when manufacturers packaging units are opened to enable the supply of smaller quantities.  

Distributors serious about ESD are able to position themselves as supply chain partners that understand the importance of static handling and are therefore a valuable supplier to OEMs producing electronic equipment. Establishing a strict ESD control policy will effectively eliminate all potential electrostatic damage at the distribution stage.

Naturally, once the components leave the distributor, ESD protection is equally important at the OEM assembly stage of the manufacturing process. Here, there are many things that can be done to avoid the unwanted effects of ESD.

The use of mats and wrist straps remain common industry practice. For instance, layered runner mats can be installed on bench-tops where electronic components are assembled, while grounding cords can be attached at each bench and connected to earth for rapid dissipation of static charges. Grounded wrist straps should of course be used by all personnel handling, inspecting and packing electronic devices to help prevent electrostatic damage to any sensitive device or equipment. Wrist straps comprise a conductive band with a series resistor (to avoid static sparking through abrupt dissipation) connected through a wire and alligator clip to a ground or reference point.

Where there are wrist straps, there should also be wrist strap testers, particularly in areas where PC boards are populated and products are assembled. Testers are deployed to measure the effectiveness of wrist straps and their path to ground.

ESD wrist straps will safely ground a person working with sensitive electronic equipment and prevent build up of static electricity on their body that otherwise could eventually result in an electrostatic discharge.

Most companies serious about ESD will insist that their operators continuously carry out operational checks of the wrist straps. The person wearing the wrist band goes to an ESD test station and attaches the alligator clip to the ground terminal. While the person touches a finger to another test metal plate, the machine adds an electrostatic potential to the person's body. If the voltage climbs, the wrist strap has failed, whereas if the ground effectively keeps the voltage down, the strap is good for continued use.

Beyond obvious measures, there are many extra initiatives that can be implemented to further combat ESD. For instance, static shielding tote boxes and bags must be used for the storage and transportation of any ESD sensitive electronic components and loaded PC boards. It is even feasible to install conductive floor tiles, which are made to conduct static charges from personnel to ground, and to prevent the accumulation of static when walked upon. Engineered ESD flooring materials including conductive tiling, surface coatings and finishes, provide an economical and effective, additional means to ground personnel. In practice flooring with a bleeder resistance of 1MΩ has proven most suitable to impede any sparking during sudden discharge while the fading time is kept to a minimum.

The selection of an effective ESD floor covering for controlled environments should commence with a comprehensive evaluation of the intended use and potential future uses. Appreciating the requirement for and importance of ESD compliant footwear is vital in the performance of the selected ESD flooring. Always remember that personnel grounding require effective ESD footwear that is appropriate to the application, worn properly, and in good repair.

Grounded foot straps are another ESD prevention measure growing in popularity throughout the electronics industry. These can be used by personnel who are not stationary within the containment areas and handle sensitive components. Operators should be required to continuously test the effectiveness of the grounded foot straps.

Training programmes for all personnel expected to handle or transport electronic devices will serve well to help educate operators in the importance of ESD protection, while all ESD protected areas must be identified clearly by prominent warning signs and caution labels. Access to such areas should be restricted only to personnel who are ESD trained. Visitors should be accompanied by ESD trained personnel and receive proper instruction before entering the protected area.

Taking ESD seriously is a matter for the entire electronics supply chain, from the manufacturer, through the distributor to the customer and beyond. By implementing a thorough ESD policy, the end user will be protected from disappointment, while OEMs and retailers will be protected from expensive refunds and loss of reputation. Beside the complete ESD compliant component shipping solution, Conrad also offers ESD accessory - from ESD gloves to access systems - for any need.

DIN EN 61340-5-1

The DIN EN 61340-5-1 also known as IEC61340-5-1 standard governs the ‘Protection of electronic devices from electrostatic phenomena - General Requirements’. It is accompanied by a User Guide DIN EN 61340-5-2 (IEC61340-5-2).

Generally IEC61340-5-1 specifies technical requirements for the design, use and control of a protected area ensuring minimal risk of damage, during the handling of electrostatic sensitive devices (ESDs) of 100V or higher sensitivity, from procurement through to end of life.

The standard covers the following technical requirements:

• The electrostatic protected area (EPA) including requirements for protective equipment, construction of the EPA, working practices, and field work,
• Grounding and bonding systems,
• Personal grounding,
• Training requirements,
• Compliance Verification (test, measurement and auditing),
• ESD protective packaging,
• Marking.

The 61340-5-1 General Requirements are considered mandatory for anyone wishing to set up an ESD protected area or facility, however a so called ‘tailoring’ process can elucidate if, on technical grounds, some of these requirements are unnecessary or irrelevant. Exceptions must be documented in an ESD Programme Plan.

With regard to the planning and documentation of an ESD programme, there are three plans to be put in place: an ESD Control Programme Plan, a Compliance Verification Plan and an ESD Training Plan.

This all also requires the appointment of an ESD coordinator responsible for implementing the requirements of this standard.

Using an antistatic wrist straps with alligator clip

ESD wrist straps will safely ground a person working with sensitive electronic equipment and prevent build up of static electricity on their body that could eventually result in an electrostatic discharge. The right application of the wrist strap is vital to safeguard both the person and the equipment.

The straps needs to be placed tightly around the wrist and is usually worn on the non-dominant hand. Loose straps are unlikely to work effectively. The grounding cable attached to the wrist strap needs to be connected to a non-painted metal portion of an antistatic matt, workbench or computer case and should remain attached during the work with, or on any, electrical equipment in and ESD protected zone.