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Question Currently we are implement ESD control. Is it a necessary for a PCBA industry must implement to wear ESD smock and antistatic seating if we already have the ESD shoe, wrist strap and finger cot? Shall all chair at the production floor must be grounded? Please suggest a cheapest way to ground the chair. If the chair which grounded by using a chain, is it compliance to the ESD requirement. Appreciate your reply soon. Thank you.
Answer

Garments and Seating are listed as EPA [ESD protected Area] ESD Control Items in Table 3 of ANSI/ESD S20.20-2007, however, it is up to the user to decide to require them as part of their ESD control program. “An EPA [ESD protected area] shall be established wherever ESDS [ESD sensitive] products are handled. However, there are many different ways to establish ESD controls within an EPA. Table 3 lists some optional ESD control items which can be used to control static electricity. For those ESD control items that are selected for use in the ESD Control Program, the required limits and test methods for that item becomes mandatory.” [ANSI/ESD S20.20 section 8.3 ESD Protected Areas (EPAs)]

ESD Smocks protect ESD sensitive items from charges that generate on workers’ clothing. Per ESD Handbook ESD TR20.20 paragraph 5.3.13.1 “While a person may be grounded using a wrist strap or other grounding methods, that does not mean that insulative clothing fabrics can dissipate a charge to that person's skin and then to ground. Clothing usually is electrically separate or isolated from the body.”

Outfitting employees with Statshield ESD Smocks is a practical way of meeting “If the field exceeds 2,000 volts/inch, … Separate the insulator from the ESD-sensitive device by a distance of 30 cm (12 inches)” [ANSI/ESDS20.20-2007 section 8.3]

The cheapest manner to ground an ESD Chair is via a drag chain to an ESD Floor. If test data can be shown that it reliably meets the < 1 x 10E9 ohm required limit of S20.20 Table 3, it would be acceptable, however, I am concerned that it would not reliably provide a path to ground. Drag chains are often used to ground ESD carts or trolleys, but tribocharging is more likely to occur when the cart is moved, and the drag chain likely more reliable as it is jostled around on the ESD floor. Conductive casters would be a superior way to ground an ESD chair or ESD cart to an ESD floor, particularly while stationary.

 
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