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What is ESD | Electrostatic Discharge basics

This page covers ESD (Electrostatic Discharge) Basics, ESD classes, sources of ESD, protection mechanism and devices and Electrostatic Discharge(ESD) tester.

When two surfaces which are in contact get separated, some atom electrons will move. This causes imbalance. Here one surface has positive charge and the other has negative charge.
Examples of ESD: Lighting, zap from a door

In general, ESD is the transfer of electrostatic charge between bodies (or between surfaces) at different electrostatic potential.

ESD - Electrostatic Discharge

Following table-1 mentions examples where in large charges are generated at all the time. People discharge frequently, but to feel it must be about 3000 volts. ESD which a person can not feel will damage the electronic components very easily. The voltage about 100 volts or less can damage the components. Smaller components mean greater sensitivity to ESD. Damage to these components can not be detected by the naked eye.

Charges generated due to Voltage level
Walking across a carpet 1,500 - 35,000 volts
Walking over untreated vinyl floor 250 - 12,000 volts
Vinyl envelope used for work instructions 600 - 7,000 volts
Worker at a bench 700 - 6,000 volts
Unwinding regular tape 9,000 - 15,000 volts
Table-1 Typical Voltage Levels of Charges Generated

Like we have adopted methods to control germs in medicine, we need to adopt and use various ESD protection devices/methods to control ESD(Electrostatic Discharge). Following table mentions ESD classes with sensitivity levels and various electronic components affected by them.

ESD Class Sensitivity Device names
ESD Class 0 <250 Volts SAW, JFETS, CCDs, Precision voltage regulator diodes, OP AMP, Thin film resistors, Integrated circuits, Hybrids utilizing class 1 parts, VHSI, CSCRs
ESD Class 1 250 to 1999 volts -Same as above-
ESD Class 2 2000 to 3999 volts JFETs, ICs, VHSIC, Precision resistor networks (type RZ), Hybrids utilizing class 2 parts, Low power bipolar transistors
ESD Class 3A 4000 to 7999 volts JFETs, OP AMPS, ICs, VHSIC, All other microcircuits not included in class 1 or class 2, Small signal diodes, General purpose silicon rectifiers, Opto-electronic devices (LEDs, phototransformers, opto couplers), Resistor chips, Piezo electric crystals, Hybrids using Class 3 parts
Table-2 ESD Class

Principle sources of ESD in ICs

• A person walking on synthetic floor can accumulate about 20Kvolts. This is discharged when he/she touches anobject which is at ground potential.
• Equipment accumulate static charge due to improper grounding. The charge gets through ICs when it is placed on test sockets.
• ICs themselves get charged during transport and when they come in contact with charged objects.

ESD Models- Human Body Model, Machine Model, Charge Device Model

ESD Human Body Model

Figure-2 depicts ESD of a Human Body referred as Human Body Model(HBM).
Peak current is about 1.3A, rise time is between about 10 to 30 ns.

ESD Machine Model

Figure-3 depicts ESD of a Machine referred as Machine Model(MM).
Peak current is about 3.7A, rise time is about 15 to 30 ns and Bandwidth is about 12 MHz.

ESD Charge Device Model

Figure-4 depicts ESD of a Charged Device referred as Charge Device Model (CDM).
Peak Current is about 10A, Rise time is about 1 ns.

ESD protection mechanism

• ESD protection circuits as mentioned for different model
• Current Limiting Characteristics of n-well Resistors
• Avalanche Multiplication in pn-junctions
• Avalanche Breakdown of nMOS
• Thermal Breakdown of nMOS

ESD Protection Devices

• n-well Resistors
• Gate-Grounded nMOS Transistors (GGNMOS)
• Gate-Coupled nMOS Transistors (GCNMOS)
• Silicon Controlled Rectifiers (SCR)
• Medium Voltage Triggered SCR

ESD Tester or ESD test equipment manufacturers/vendors

Following table mentions ESD tester or ESD test equipment manufacturers or vendors.
• Advanced Test Equipment Corp. (http://www.atecorp.com/) {ESD Gun, ESD Simulator}
• Thermo Fisher Scientific Inc. (http://www.thermoscientific.com/) {ESD Tester}
• TREK, INC (http://www.trekinc.com/), (ESD Audit Equipment, ESD Test Equipment}
• HV TECHNOLOGIES, Inc. (http://www.hvtechnologies.com/)
• United Static Control Products (http://www.ultrastatinc.com/)
• ESD testers and Meters (http://www.esdmeters.com/)
• Botron Company Inc. (http://www.botron.com/) {ESD table mat, floor mat, equipments, wrist straps, gloves, chairs etc.}

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