Electrostatic Discharge (ESD) destroys electronic hardware. As electronics becomes more miniaturized, they become more sensitive to ESD. Latent defects, defects that can injure the hardware but not destroy it, can reduce hardware reliability and cause system failures for the customer. ESD can be controlled with proper precautions. Operator training is the most important feature within any ESD Program. The maintenance of ESD workstations and ESD Protective Smocks are critical, since the operators use these items in assembling the hardware.

A typical ESD workstation should be wired in accordance to ANSI / EIA-625; Requirements for Handling Electrostatic Discharge Sensitive (ESDS) Devices. A common ground point is used to connect the ESD Bench Mats, ESD Floor Mats and ESD Wrist Straps. The common ground point can be either to earth ground or electrical (system) ground. All equipment, such as soldering irons through light fixtures, are grounded through electrical (system) ground at the power receptacles.

The environment plays an important role in controlling ESD. The work center's Relative Humidity must be held between 30% and 75%. Low Relative Humidity is a source for ESD due to the friction of airborne particles.

To maintain a workstation, there are a few rules to adhere to:
Regularly check the common ground point for continuity to earth or electrical (system) ground. Many times, during operation or a facility rearrangement, a workstation loses its ESD protection because the common ground point becomes disconnected to earth or electrical (system) ground.
Poor ESD workstation practices can cause ESD failures. A cluttered workstation, food and drink on the workstation, non - ESD hand lotion and lab coats, unprotected hardware, and using non-ESD packing materials can reduce ESD protection (Figure 1-top).

Good ESD workstation practices are good manufacturing practices. A workstation should be clean, with no extraneous material. All materials, equipment, and hardware are grounded (Figure 1-bottom).

In various electronic manufacturing forums, there have been some discussions on the use of ESD lab coats. An ESD lab coat has carbon fibers woven into the lab coat. The coat serves as a Faraday cage between the operator and the hardware. When properly used, it reduces the possibility of a charge being transferred from the operator to the hardware.

When wearing an ESD lab coat, there are several good practices to follow:

•No jewelry should be exposed. The sleeves are to be cuffed or buttoned at the wrist, with only the ESD wrist strap cord being exposed.

•Depending on the type of ESD lab coat used, the top button may be unbuttoned. However, when an ESD lab coat is also used to prevent hardware contamination, the top button should be buttoned.

•ESD lab coats should be cleaned regularly and be undammaged. ESD lab coat manufacturers provide recommendations on how the lab coats are to be cleaned. In general, ESD lab coat manufacturers either dry clean their lab coats or use a mild detergent. Several ESD lab coat manufacturers offer cleaning services to their clients.

•To be in compliance to an ESD Control Plan, the cleaning processes must be formally documented, whether the cleaning processes are performed internally or outsourced. It is recommended that the ESD lab coats not be cleaned at home by operators. If the ESD lab coats are taken home, there will be no consistency in cleaning practices used by the workforce. Improper cleaning procedures can damage the carbon fibers woven into the ESD lab coat.

For additional information regarding ESD workstation safety guidelines, contact the EMPF Helpline at 610-362-1320 or helpline@empf.org.