ESD Systems - Questions And Answers

We are manufacturing digital exchanges / switches for telecom. We have measured surface resistivity of the mosaic floor in testing areas thro surface resistivity meters and got the readings in the range of static dissipative ( 100 M ohms to 1000 Mohms/sq).As per British stds 2050: 1978, the surface resistance of the floor forantistatic should be from 100 K ohms to 100 M ohms.We have alsomeasured the relative humidity in the testing areas and got the readingsof RH as 45 to 55% ( in air condtioned areas). We are wearing antistatic coats to prevent accumulation of staticcharges on the body of the testing staff. We intend to use wrist straps - the other end of which will be connected to esd ground thro a safety resistor of 1 M ohm.We hope with the above ESD measures, we can have an effective ESD control.We seek your expert advice- whether the above measures are sufficient for an effective ESD control. Whether we need to use floor mats on the mosaic floor. Or whether we need to ground the corners of mosaic floor to provide a discharge path.

Our country as you are aware is a tropical counrty. In our testing areas where we test our exchanges, the relative humiditymeasured is 50% (in air conditioned areas) and surface resistivity measured onthe non grounded mosaic tiles surface of the floor is within the range of 100to 1000 M ohms/sq. Our testing staff in testing areas , wear anti static coats and wear wriststraps with 1 M ohm resistor- connected to seperate esd ground. Under the above conditions, Is it required to have conductive /staticdissipative floor mats to be laid in the testing areas Or the above measuresare sufficient to have an effective esd control. If the above measures are sufficient, is it required to measure resistence toground - from the mosaic surface to esd ground. Also intimate me about the testprocedure to measure rtg. Anonymous, Bangalore, India

The ESD Association Flooring standard ANSI ESD S7.1, < 1x10⁹ ohm as listed in the ANSI/ESD-S20.20-1999. So your measurement of 1,000 megohms meets this criteria.You will want to measure the resistance of the floors surface to the ESD ground. This resistance (sometimes referred to as an RTG measurment) will tell you how effective the floor is to providing a conductive path to ground. If this path is less than 1x10⁹ ohms (1,000 megohms) then it will suffice to remove charge imbalance from mobile workers and equipment (i.e., carts with drag chains).The other control practices are in line with the ANSI/ESD-S20.20-1999 as well.You can download a free PDF copy of the ANSI/ESD-S20.20-1999.

From what you described, personnel wearing grounded wrist straps at the test area, there is no immediate need for ESD flooring in these areas as long as the personnel are grounded via wrist straps before opening ESD protective packaging on ESD protective work surfaces. Whether or not to use grounded conductive or dissipative floor mats depends on the operations of the personnel, the completeness of your ESD Control Plan and the sensitivity of the ESD Susceptible devices being handled by the personnel. The safest response is yes, but in conjunction with ESD foot wear.If ESD susceptible devices are being brought into the test area without being protected by proper ESD control packaging or procedures, then the packaging needs to be corrected and ESD floors will help.

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