In a previous post, we talked about ESD: what it is, what types of ESD damage there are and what costly effects ESD can have. Missed it? Catch-up here. In this post we will start to uncover how we control ESD, but where to start? We figured the best place would be with the EPA, the Electrostatic Protected Area, but before we dive in let’s have a brief overview of the basic principles of ESD Control:
Most of these principles are carried out in the designated EPA. If you implement all three points above correctly, and have a well-defined EPA, you should be in control of ESD and your sensitive items will be protected. To understand how to implement these principles, first we must understand “What is an EPA?”.
An EPA is a defined space where all surfaces, objects, people and ESD Sensitive Devices (ESDs) within it are kept at the same electrical potential. This is achieved by simply using ‘groundable’ materials (i.e. materials with an electrical resistance typically of less than 109 ohms) for covering all surfaces, for containers and for tools. All surfaces, products and people are bonded to Ground, which means connecting them with a resistance of < 1 gigohm. Movable items (such as containers and tools) are bonded by virtue of standing on a bonded surface or being held by a bonded person. Everything that does not readily dissipate charge (an insulator), should be excluded from the EPA, except for when process essential, in which case Ionisation can be used.
An EPA could be anywhere from just one workstation, a room, or a whole factory floor. It can even be portable, perhaps in a field service situation.
So, in summary, in an EPA you:
For your ESD control programme to be effective it is very important to define where the EPA is and to include this in employee training. This is so that each employee, whether they regularly work within the EPA, or are an occasional visitor, know when and where they need to take ESD Control measures, such as wearing ESD footwear and Static Control Garments. In addition, it informs employees when the shielding of ESD Sensitive Devices is required. If the ESD Sensitive Devices is outside the EPA it pretty much guarantees it is no longer grounded, the device should be put in a closed shielding bag or container while it is still grounded and still in the EPA.
The entrances, and if necessary, the boundaries, should be identified; this will depend on the type of area and whether there are physical boundaries already in place. Products such as floor marking tape and signs can be used to attract attention and deliver a clear message to personnel and visitors. You might use terms such as “Attention: ESD Protected Area”, “Observe precautions for handling electrostatic discharge sensitive devices”, “You are entering an ESD Protected Area”, etc.
In its simplest form, an EPA area is a basic workstation and consists of the following components:
To create an EPA:
By following the above steps, each element connected to the EBP Plug (the surface and the operator) are kept at the same electrical potential and any electrostatic charge is being removed to ground via the EBP Plug. The EBP Plug provides a common ground point for grounding using protective earth. The plug fits into the mains supply socket, making a connection with the earth conductor only. In place of the live and neutral pins are moulded insulating plastic pins to allow positive location in the socket.