Introduction of anti-static wrist strap, heel strap, conductive shoes
Workers need to use an anti-static wrist strap to ground is the main means of ESD control. For the static charge generated by the human body during normal movement, the personnel grounding equipment can provide a permanent grounding path. These tools can take many forms, such as:
Anti-static wrist straps are considered the first line of defense against ESD, and wrist straps should be used in most ESDS working environments. Metal contacts are better than conductive plastics. The wristband cuff should always be in direct contact with the exposed skin of the operator. Do not wear it on clothing. The use of bead-type chain wristbands is prohibited.
The anti-static wrist strap should always be close to the skin and cannot be hung arbitrarily. During the initial certification, the electrical integrity of each wristband should be checked and verified by the operator at the beginning of each use shift. A wristband checker specially designed for this purpose will be used to verify that the wristband is working properly. The wrist strap of each workstation should be grounded using a common ground point. ESD S6.1 "Recommended Grounding Practices" outlines recommended grounding practices.
It is strongly recommended to use a continuous online continuity checker. (Refer to ESD TR20.20-2008, Section 5.3.9-Continuous Monitor). The wristband resistance measured between the other hand and the (ungrounded) ground terminal of the wristband assembly must not exceed 9M ohms of the current limiting resistance value included. Work surface materials that dissipate static electricity must not be used as part of the ground path of the wrist strap.
For more information about wrist strap testing and setting, please refer to ESDS1.1 "ESD Standard Test Method for Protecting ESDS Items-Wrist Strap".
Leg straps, anti-static heel straps and conductive shoes. When using wrist straps is impractical or unsafe, when using leg straps, heel straps and conductive shoes as acceptable alternatives to wrist straps, conductive/dissipative flooring is required And/or conductive floor mats. Examples of this situation include when working near moving conveyor belts or wave soldering machines and when working on large systems. The built-in resistance of the foot strap should be 1X106 +/- 20%. If the resistance does not meet the recommendation, the value should be approved by an ET&V official.
ET&V officials should measure the conductivity of heel straps and conductive shoes during initial certification. The operator should verify this conductivity in each work shift. The test method is found in ESD S9.1 "ESD Association Standard Test Method for the Protection of ESDS Sensitive Items-Footwear-Resistance Characteristics".