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Questions And Answers

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Question

a.) Is ESD typically measured in volts or kv?

b.) When considering a "dangerous" measurement for an electronic device...what is the minimum measurement?  

I hear numbers like 25 and 100...but do not understand if this is in volts or kv.

Thank you... 

Answer

The measurement of ESD sensitivity is withstand voltage, measured in volts.

Some end users assume that all electronic components are ESD Susceptible, however, others write their ESD control plan based on the device and item susceptibility or withstand voltage of the most sensitive components used in the facility. Typically, the easiest way to establish the ESD susceptibility of ESDS items in your facility is to obtain the information from the manufacturer. A reference book, not published since 1995, is available from the Reliability Analysis Center “V-ZAP” data book.

The ESD Association has developed three models to determine the ESD sensitivity of electronic components:

(1) Human Body Model (HBM) [100 pF @ 1.5 kilohms], ESD STM5.1

(2) Charge Device Model (CDM) [4 pF/30 pF], ESD DS5.3.1

(3) Machine Model (MM) [200 pF @ 0 ohms], ESD STM5.2

These documents can be downloaded for no charge from the ESD Association web site at www.ESDA.org

Human Body Model

The most common model is the HBM. This model simulates when a discharge occurs between a human (hand/finger) to a conductor (metal rail). The equivalent capacitance is 100 picofarads (100 x 10^-12 Farads) and equivalent resistance is 1,500 ohms to simulate a human body. The typical rise time of the current pulse (ESD) through a shorting wire averages 6 nanoseconds (6x10^-9 s) and larger for a higher resistant load. The peak current through a 500 ohm resistor averages 463 mA for a 1,000 volt pre-charge voltage.

Per ESD-STM5.1 Human Body Model (HBM)Component Level paragraph 4

Table 1-HBM ESDS Component Classification
Class Voltage Range
0 < 250
1A 250 to < 500
1B 500 to < 1000
1C 1000 to < 2000
2 2000 to < 4000
3A 4000 to < 8000
3B > or = 8000

ANSI/ESD S20.20 is the ESD Association standard is “for the Development of an Electrostatic Discharge Control Program for – Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices)”. The purpose of this standard is “to provide administrative and technical requirements, as well as guidance for establishing, implementing and maintaining an ESD Control Program. The document is based upon protecting electronic parts, assemblies and equipment that is “susceptible to damage by electrostatic discharges greater than or equal to 100 volts Human Body Model”.

Per Handbook ESD TR20.20 section “The 100 volt Human Body Model limit was selected for ANSI/ESD S20.20 as the baseline susceptibility threshold since a large majority of the ESD products on the market have a sensitivity of greater than 100 volts.”

Also at www.ESDA.org is a White Paper, “ESD Phenomena and the Reliability for Microelectronics” downloadable at no charge which predicts that more sensitive electronics, that is lower withstand voltages. As “electronic industry continues to scale microelectronic structures to achieve faster devices, new devices, or more per unit area. Secondly, electrostatic charge, electrostatic discharge (ESD), electrical overstress (EOS) and electromagnetic emissions (EMI) continue to be a threat to these scaled structures.”


There are more sensitive items with very low withstand voltages being used today; an example is magneto-resistive heads in disk drive manufacturing.

 
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