AET Electrostatic Discharge (ESD) and Component Handling ā Questions and Answers
Question 1: What is the primary danger of improper ESD handling when working on avionics circuit boards?
- Mechanical damage to solder joints from static 'snap' forces
- Invisible damage to semiconductor junctions that may cause immediate failure or weaken the component for later in-service failure (Correct answer)
- Contamination of connector contacts with static-attracted dust particles
- Thermal damage to nearby wire insulation from the heat of the discharge
Correct answer: Invisible damage to semiconductor junctions that may cause immediate failure or weaken the component for later in-service failure
A static discharge can damage or destroy the extremely thin gate oxide layers in MOSFETs and other semiconductor junctions without any visible sign. 'Latent' ESD damage may not cause immediate failure but will reduce the device's reliability and life span.
Question 2: When must a technician wear a properly grounded ESD wrist strap while working on avionics?
- Only when working in environments with relative humidity below 30%
- Only when handling radar or high-power transmitters
- Whenever handling any ESD-sensitive (ESDS) device or assembly, regardless of environment (Correct answer)
- Only when wearing synthetic fabrics that generate static electricity
Correct answer: Whenever handling any ESD-sensitive (ESDS) device or assembly, regardless of environment
ESD-sensitive devices must be protected regardless of humidity, clothing type, or work area. Even low static levels invisible to human senses can damage ESDS components. The wrist strap provides a continuous path to drain static charge safely.
Question 3: What resistance value should a properly functioning ESD wrist strap measure when tested with a wrist strap checker?
- 0 ohms (dead short to ground)
- Approximately 1 megohm (1 MĪ©) (Correct answer)
- Greater than 100 megohms (open circuit)
- Less than 10 ohms
Correct answer: Approximately 1 megohm (1 MĪ©)
A correctly functioning ESD wrist strap contains a 1 MĪ© resistor in series. This provides enough resistance to protect the technician from electrical shock while still allowing static charge to drain safely to ground. A dead short (0 Ī©) would create a shock hazard.
Question 4: How should an ESD-sensitive avionics LRU be transported between the aircraft and the avionics shop?
- Carried directly in both hands to maintain physical control of the unit
- Placed in a standard cardboard box padded with foam rubber
- Transported in approved ESD-protective (conductive or dissipative) packaging (Correct answer)
- Wrapped tightly in plastic bubble wrap to prevent physical damage
Correct answer: Transported in approved ESD-protective (conductive or dissipative) packaging
ESDS assemblies must be transported in approved ESD-protective packaging ā conductive bags, dissipative foam, or other approved containers. Standard cardboard and plastic bubble wrap are insulators that can generate and hold static charge, increasing the risk of ESD damage.
Question 5: What does the international ESD symbol (a hand inside a triangle with a diagonal bar) on an avionics component label indicate?
- The component requires special torque tools for installation
- The component is ESD-sensitive and requires proper ESD handling procedures (Correct answer)
- Only personnel holding an ESD certification badge may handle the component
- The component contains a radioactive source used for calibration
Correct answer: The component is ESD-sensitive and requires proper ESD handling procedures
The ESD symbol (hand-in-triangle with slash) is the internationally standardized marking indicating that the item is ESD-sensitive (ESDS) and must be handled, stored, and transported using ESD protective measures to prevent damage.
Question 6: What is 'latent ESD damage' in an avionics component?
- Damage that occurs only during an actual lightning strike on the aircraft
- Partial damage that does not cause immediate functional failure but degrades the component so it fails prematurely during service (Correct answer)
- Damage detectable only by electron microscope imaging immediately after the ESD event
- Surface pitting on connector pins caused by repeated discharge events
Correct answer: Partial damage that does not cause immediate functional failure but degrades the component so it fails prematurely during service
Latent ESD damage is the most dangerous form because the component passes all functional checks immediately after the ESD event but has weakened semiconductor junctions. The component then fails in service ā often in a mission-critical situation ā long after the original handling error.
AET Electrostatic Discharge (ESD) and Component Handling
What is the primary danger of improper ESD handling when working on avionics circuit boards?