The basics of ESD safety
Touching a car door can be all it takes to get a slight electric shock, or electrostatic discharge (ESD). However, the fact humans can only sense an ESD of 3,500 volts or more makes it a risk factor for the manufacture or processing of electronic components. After all, these are areas where a discharge of just 100 volts is enough to cause weakness in components, yet staff rarely notice such incidents. Unidentified ESDs threaten not only product quality but also, over the long term, the success of a company. That makes it vital to systematically implement an ESD safety concept.
Like a lightning strike during a storm, only on a much, much smaller scale – that’s the kind of effect an ESD has on electronic components. The problem is that in industry these discharges either go unnoticed or their effects are simply underestimated due to inadequate knowledge of the issues involved. However, without precautionary measures, an ESD can occur early on when at-risk electronic components first arrive at the company or at any point in the production chain – right up to the moment when the final product is delivered to the customer.
Risk factors and effects of ESD
For an electrostatic discharge to occur, a charge first needs to accumulate. This builds up as a result of friction, separation or straightforward contact between any two materials with different electrostatic potentials. Where the two materials are identical, differences in potential can be caused by moisture or impurities. Exacerbating factors include synthetic clothing and insulating footwear, unsuitable tools and factory equipment, textile floor coverings and conventional office chairs. However, a charge can also be transmitted to an electronic component via nearby material that has already accumulated a charge. When it comes to people, simply walking across the floor can be all it takes to build up a charge. When two differently charged materials later come into contact, there is an uncontrolled equalisation of charge.
In retrospective examinations conducted using electron microscopes, electronic components damaged by an ESD reveal visible fusing and craters on the silicon surface. The more delicate a component’s individual structures are – for example, those of an electronic chip – the more sensitive they are to an ESD. One particular characteristic of an ESD is that, often, it does not render the affected components unusable straight away. However, they do not initially exhibit any defects during quality assurance, meaning they – along with their damaged transistors and circuit paths – are then used for subsequent steps in the value-added chain or are delivered straight to the customer.
(Financial) consequences of damage
If the damaged component is delivered to the customer, its failure there can have any number of effects. What seem at first glance to be the obvious consequences of ESD damage include complaints, warranty payouts and costs incurred due to rejects and repairs. Yet customers may also withhold payment until the delivered parts are proven to be in perfect working order. The necessary design verifications and the subsequent troubleshooting in the event of ESD damage often take more time and effort than implementing an ESD safety concept. Furthermore, damaged electronic components emanating from your own production undermine customers’ trust in your business in the medium term. In the worst-case scenario, if failures occur in areas critical to production, this could incur liability for damaged products or even lead to the company’s supplier status being withdrawn. From a production worker’s perspective, this is frustrating, as they are unable to identify the fault due to the absence of visible damage and their unfamiliarity with ESD. This wide range of different risk factors gives rise to various ESD safety requirements that have to be met in full and continuously as part of a safety concept.
ESD safety concept calls for trained personnel
An ESD can be triggered by a wide range of factors within a production environment, which means effective countermeasures need to be actively established throughout the entire company and subjected to regular inspection. For this purpose, the DIN EN 61340-5-1 standard prescribes an ESD control programme that sets out the key components of a customised concept that is binding on all staff. One part of such a concept is a safety procedure for the entire process chain, including suppliers and customers. ESD coordinators and staff need to be well trained and wear standard-compliant protective clothing. In the protected areas, which also need to be in line with industry standards, all relevant aspects need to be inspected on a daily basis. Compliance with personal safety provisions and regular internal audits also feature among the requirements.
An appropriately trained workforce with an understanding of ESD-related issues forms an integral part of the implementation process. item Industrietechnik GmbH has therefore developed a free e-learning course for its item Academy learning platform, for example. Staff are given a compact and easy-to-understand overview of the topic, broken down into four sections. The course starts by exploring the background of ESD before subsequently setting out the associated problems in a multimedia and interactive format. As participants progress, it also becomes clear to them just how much each staff member contributes to dependably implementing an ESD safety concept. The course also covers dealing with ESD-sensitive components, practical tips on avoiding ESD damage and how staff should conduct themselves in an electrostatic protected area (EPA). The two white papers “The basics of ESD safety” and “The 10 golden rules of ESD safety” enhance the item e-learning portfolio and offer all the facts and figures relating to ESD at a glance.
Working within an EPA
An EPA is an ESD safety zone. It can take the form of a single work bench, a defined space or an entire building. The underlying principle is that electronic components must be handled and assembled exclusively in these areas. All material used within them therefore needs to be electrostatically dissipative and earthed to the same potential. This ensures electrostatic charges and differences in potential are reliably avoided. In contrast to unprotected areas (UPAs), only trained personnel and visitors who have been given suitable instruction with the appropriate protective equipment may enter an EPA. Moreover, only trained members of staff are permitted to handle ESD-sensitive components.
Numerous elements are integral to any EPA. A special conductive ESD floor, for instance, will safely dissipate the kinds of electrical charges that can form as a staff member walks across the floor. However, it is of little use if the staff in that area don’t have an electrical contact with the ground. Normal shoes often act as insulators. In contrast, conductive footwear or shoe earthing strips establish a conductive connection between the body and the ESD floor. Low humidity also exacerbates the formation of electrostatic charges. The relative humidity in the areas requiring protection should be kept to at least 30 percent, if the building structure allows for this.
As far as possible, no chargeable materials must be used in the handling area as a general rule. Every time electronic parts are transported or placed in storage, particular care should be taken to provide them with adequate protection, for example by using appropriate containers and trolleys. Profile and fastening technology from item can be designed to be electrostatically dissipative, for instance. Overall, all parts used should be viewed as ESD-sensitive – even if the actual risk varies depending on the material and design.
Risk factors for electrostatic charges are found at virtually any point in the process chain, while the causes of ESD damage are equally wide-ranging. Components can suffer damage as early as the delivery and storage stages, but also in the quality assurance phase. Inadequately protected systems, equipment and staff pose a risk during production and assembly. It takes a comprehensive and systematically implemented ESD safety concept – including in conjunction with collaboration partners and service providers – to rule out, as far as possible, all such weaknesses, which have a lasting serious impact on a company’s success.
Length: 8,813 characters including spaces
Date: 18 February 2020
Caption 1: Only trained staff and visitors who have been given suitable instruction with the appropriate protective equipment may enter an ESD safety zone – also referred to as an EPA. Source: item
Caption 2: In retrospective examinations conducted using electron microscopes, components damaged by ESD reveal visible fusing and craters on the silicon surface. Source: item
Caption 3: As employees both carry and transfer charges, they must wear an ESD wristband to prevent the accumulation of electrostatic charges when handling ESD-sensitive components. Source: item