Electrostatic Sensitive Devices Quiz

Electrostatic Sensitive Devices (5.12)

• Learning objectives include special handling of components sensitive to electrostatic discharges (Level 2)
• Understanding the risks and possible damage caused by electrostatic discharges (Level 2)
• Knowing about component and personnel anti-static protection devices (Level 2)

Static Electricity

• Static electricity is an electrical charge at rest, unlike current electricity
• It can be generated by friction or induction
• Triboelectric charge is the build-up of static electricity through friction
• Walking across a carpet can generate a static charge of up to 35,000 volts on the human body
• The body can feel a shock from a discharge of 3000 volts
• Damage to electrostatic-sensitive circuits can occur from a discharge of only a few hundred volts
• Arcing indicates the discharge or equalisation of a potential difference.

Induced Static Charges

• Simple induction occurs when a conductor is in the presence of an electrostatic field
• Positive and negative charges separate on the conductor
• The electrons are attracted to the positive charge
• The same effect happens with strong magnetic fields
• Upon removal, electrons rush back to neutralise the imbalance, creating a current that could damage the circuit
• Sensitive integrated circuits (ICs) can be damaged by external magnetic or electrostatic fields, even without direct contact with an ESD source.

Compound Induction

• If a conductor is grounded, it can attract more electrons, further increasing the electrical potential
• Removing the ground creates a net negative charge
• When the field is removed, the charges equalise, resulting in a negative potential across the conductor's surface
• This is compound induction

Dangerous Situations Generating Static Charge

• Low relative humidity (10-20%)
• Walking on carpets
• Walking on vinyl floors
• Working at a workbench
• Using vinyl envelopes
• Handling polythene bags
• Sitting in a chair with urethane foam

Metal-Oxide-Semiconductor Devices

• MOSFETs are very susceptible to ESD damage
• Parts susceptible to ESD damage are those in any logic family, requiring small energy changes or voltage changes.
• Examples are NMOS, PMOS, CMOS, and TTL items.
• ESD damage can damage components through arcing through the insulating silicon dioxide layer
• External magnetic or electromagnetic fields can also damage components

ESD Sensitivity

• Human Body Model (HBM) is a test method measuring ESD sensitivity
• A charged 100-pF capacitor is discharged into the device via a 1500-Ω resistor.
• The withstand voltage is the maximum test voltage without causing damage.
• Component sensitivity levels such as VMOS, MOSFET, EPROM, JFET, OP-AMP, Schottky Diodes, Film Resistors, and Schottky TTL have varying withstand voltages

Device Sensitivity Classification

• Components with a maximum ESD withstand voltage of 16,000V or less are considered ESD sensitive.
• Classification includes:
  • Class 1 (Extremely sensitive) 0–2 kV
  • Class 2 (Sensitive) 2–4 kV
  • Class 3 (Less sensitive) 4–16 kV

Circuit Cards

• ESD-sensitive components on circuit cards are still susceptible to ESD.
• Special care is needed to prevent ESD from entering through connector receptacles.

Types of ESD Damage

• Catastrophic failures : Components are irreparably damaged (e.g., junction breakdown, metal melt)
• Latent failures: Components are weakened or degraded, leading to poor performance over time
• Upset failures: Intermittent faults or software glitches may occur, which are hard to diagnose

ESD Handling Precautions

• Do not touch the pins of components
• Do not touch the sockets, plugs, or pins of equipment
• Discharge static electricity by touching a grounded surface
• Ground the equipment during removal
• Equalise electrostatic potentials before disconnecting cables, and immediately cover disconnected plugs.
• Use designated ESD work areas
• Use conductive wrist straps while working
• Use static dissipative materials and equipment
• Use conductive packaging, like bags and trays

ESD Safe Workplace

• Requires a grounded ESD-protective work surface
• Use ESD-safe flooring
• Provide personnel grounding (like wrist straps)