ESD Tutorial Includes:
ESD Basics How ESD affects electronics components Protecting against ESD ESD protected area ESD workbench ESD work mat ESD wrist strap ESD clothing ESD storage ESD process ESD on a budget Design to combat ESD
An ESD protected area, ESDPA or just EPA is an area set up in a facility that is protected from the effects of static. It ensures that static generation and transfer is kept to a minimum and that static sensitive devices are protected.
The set up of an electrostatic discharge protected area is not just a collection of products, but it requires processes to be followed to ensure that the static sensitive devices are not subject to any discharges and damage.
By setting up and correctly using an EPA or ESD protected area, the level of failures during production and later in life will be minimised. As a result, the investment in the ESD protected area will soon repay itself both in terms of the cost of direct rework, and later in the life of the product where its reliability will be higher. Not only will this reduce costly call-outs, but long term reliability will result in customer satisfaction.
ESD protected area basics
When setting up any form of ESD protected area, there are many different measures that can be employed to provide a safe ESD environment for the electronics components, sub-assemblies and assemblies. However when setting out to set up an ESD protected area, it is necessary to carefully analyse exactly what measures are required. It is very easy to adopt an attitude where every measure possible is incorporated, but this may result in spending much more than is needed.
A carefully thought out ESD protected area can result in cost savings, especially by planning how to use the facilities to their optimum. This will combine the use of many of the ESD prevention measures, along with an efficient workflow pattern.
The key element of an ESD protected area is that it will provide an environment where any ESD build-up is minimise, and where it does occur, it can quickly dissipate naturally without being discharged through an electronic component.
The measures that can be used within an EPA can be grouped into a number of broad categories:
- ESD environment: One of the key elements of an EPA is the overall environment of the EPA. One of the key elements to be installed first is the flooring. This should be static dissipative. Suitable tiles or carpet can be installed, although carpet may need re-treating from time to time. These should have a resistance of <1.0 x 10^9 when tested as per ESD S7.1, although fully conductive tiles are not recommended for safety reasons!.
In addition to this, other items such as humidifiers to control the humidity also help. A very dry atmosphere will give rise to static. This can be noticed in a normal environment where static discharges may be noticed on a dry day, but not on a normal or damp day. Also ionisers with a +/- 50V offset tested to ESD S3.1 may be used.
- ESD workbench and ancillaries: The use of an ESD workbench with ESD straps, ESD seats, etc., to ensure the operator or user is grounded (via a high resistance dissipative rather than conductive path for safety reasons) is a key element in any ESD protected area. . . . . . Read more about the ESD workbench
- ESD tools: Another area of importance is the use of ESD tools. A variety of tools come into this category and a particular example is the use of an ESD soldering iron. Tools, and in particular soldering irons can easily transfer static directly to the components, and having a metallic element, this can provide a good transfer path resulting in high current levels that can cause more damage. Further details of ESD tools and ESD soldering irons can be found on a further page.
- ESD clothing: The use of ESD clothing is important because items of normal clothing can generate and carry static. With many more garments being manufactured from man made fibres, the risk of static is greatly increased. A whole variety of items can be obtained to ensure that the clothing worn by people within the ESD protected area does not cause issues.
. . . . . Read more about the ESD / antistatic clothing.
- ESD storage and transport: It is normally not possible to immediately utilise a subassembly within the final assembly, although this may happen in some particularly efficient flow-lines. As a result many components and sub-assemblies need to be stored. It is therefore essential that ESD prevention measures are adopted during storage to prevent damage. Ideally the storage area should follow the same EPA guidelines and be a static dissipative area.
. . . . . Read more about the ESD / antistatic storage.
- Exclusion of static generating material: many materials that are used in everyday life generate large amounts of static. These material should be excluded at all costs from the EPA. Materials such as expanded polystyrene generates very large amounts of static as generated by the fact that it sticks to everything. This must never be allowed into the area. Also some forms of bubble wrap are not good, although some types have been developed for use as ESD packaging - this often has a slight pink tint to it.
Plastic cups are also very bad in terms of retaining static (although drinks should not be allowed in an electronics work area anyway) and many other plastic items are not good because plastic is a very good insulator. Many other items may also be bad. Some people even use special ESD paper instead of normal paper for printouts and notes, although measures like these are not always implemented.
Note: values for resistance and test methods are defined in ANSI/ESD S20.20.
The creation of an ESD protected area is an essential requirement for any company manufacturing or repairing electronics equipment. It may appear to require a large investment in plant, time and effort, but manufacturing companies have no option but to implement an ESD protected area.
For field service and repair it is still necessary but the extent is more localised - portable mats and associated products can be made into a portable pack. Transport of the boards can then be arranged in suitable ESD protected bags and boxes, etc.
When setting up an ESD protected area it is possible to draw on the experience of many companies, and there are many suppliers of the products required.