Electrostatic Discharge (ESD) Workstation and Precautions

What is Electrostatic Discharge:

Sudden and rapid flow of energy between two differently charged objects.  This often creates a visible “spark” and accompanying sound crackle. The discharge is a means of balancing the extreme difference in charge between the two objects. The buildup of charge is caused when 2 different materials rub against each other, like shoes on carpet or a synthetic sweater and cotton t-shirt. Your body rubbing against air can cause a buildup of charge.

Damage from Electrostatic Discharge

A discharge of  as low as 10 volts can cause microscopic damage to integrated circuits.  To put this risk in perspective you typically can not see, feel or hear a discharge unless it is around a thousand volts. Sensitive electronics like those in computers can be damaged without any indication of the incident or visible signs to the naked eye.

Prevention

ESD Compliant workstation components

1. Conductive mat with grounding lead: The mat consists of of a conductive mesh between 2 layers of rubber or non-conductive vinyl, a “soapy” film on the mat allowing the charge to dissipate, a ground connector that goes through the mat with a 1 megohm resistor, a lead cable connected to the ground connector and a verified earth/ground like that on an outlet.
2. A wrist strap or heel strap with a 1 megohm resistor touching bare skin connected by a grounding lead either to the the grounding mat via a terminal or alligator clip or directly to the earth/ground of an outlet.
3. Ground polarity to tester to verify the outlet is properly grounded, and optionally a ground loop tester to verify that you are properly grounded. 
4. Static safe tools and supplies like static safe bags for components, non conductive tools and kapton tape.

ESD Precautions

1. Work at an ESD compliant workstation.
2. Do not handle or open any components until you are properly grounded.
3. Handle all boards by their non conductive edges, do not directly touch the metal components and circuitry of the board.
4. DO NOT GROUND YOURSELF when working with active power such as a device currently plugged in to power and energized power supplies that have not been discharged. As the purpose of grounding is to pull excess charge through the strap if a component you were to touch is plugged in or highly energized the resulting shock will be directed through your body even more efficiently and can cause serious injury or death.
5. Do not place components on a metal surface.
6. Avoid synthetic materials in the work area. Plastic bags, styrofoam cups, fleece sweatshirts, spandex, foam packaging etc should be at least 5 feet away from an active work area. Avoid clothing with these same materials, 100% cotton shirts, pants and under garments are best. Remove jackets, scarves, hats and other synthetic items when possible.
7. When possible regulate humidity in the work area between 70%-90%, this will lessen static charges. Also the use of an ionized air generator is optimal as it neutralizes charge in the air.
8. Clean and condition grounding mats regularly with a mat cleaner and conditioner to maintain the grounding properties of the mat. Do not use household cleaners on the mat.

Misunderstandings about ESD precautions

1. Touching a metal surface before working with sensitive components is good enough. Although it is true that the initial discharge from touch a metal object lessens the charge it does not prevent buildup while working. A common instruction when installing user serviceable components like those in computers is simply there because not everyone will have an ESD compliant workspace but only lessens the risk of damage.
2. You do not need to be hardwired to be grounded.  There exists some battery operated wireless “grounding” straps. Although these devices create a ground loop they do not create a true ground loop and their effectiveness can not be proven.
3. I have never had any damage to components before when working without ESD compliant grounding.  The truth is how would you know? If you are working on a component like a computer mother/logic board the microscopic damage can happen to an area that you are not immediately working on and may show up later as an intermittent issue to a completely different area of the computer. An example would be that you replace a graphics card in your computer and find later that the ethernet port does not maintain connection.

Related articles