6-2) Electro Static Discharge Safety

Question 1

What is ESD and where does it come from?

Answer 1

ESD = electrostatic discharge

ESD occurs when two surfaces have a large difference in electrical potential and the two surfaces get close enough for the voltages to suddenly equalize. This equalization produces a rapid discharge that will produce a spark.

Question 2

How do two objects get a difference in electrical potential?

Answer 2

The surfaces of the two objects obtain a difference of potential when valence electrons are pulled off or rubbed off. This can happen when pulling a roll of plastic off the roll or by walking on a carpeted floor with leather soled shoes.

Question 3

What is the largest example of ESD in nature?

Answer 3

lightnight

Question 4

What could be the ESD after walking across a carpet?

Answer 4

1,500-35,000 volts

Question 5

What could be the ESD after walking over untreated vinyl floor?

Answer 5

250-12,000V

Question 6

What could be the ESD from vinyl enveloped used for work instructions?

Answer 6

600-7,000V

Question 7

What could be the ESD from a worker at a bench?

Answer 7

700-6,000V

Question 8

What could be the ESD from unwinding a regulator roll of tape?

Answer 8

9,000-15,000V

Question 9

About how much ESD is needed for us to be able to feel it?

Answer 9

3,000V

Question 10

About how much ESD is needed to be able to seriously damage electronics?

Answer 10

100V

Question 11

What is the name of the model by with ESD is rated and what is it based on?

Answer 11

Human Body Model (HBM)

Bases the severity of ESD shock on how the human body senses the jolt.

Question 12

How many ESD classes are there and what are they?

Answer 12

ESD Class 0, Class 1, Class 2, Class 3

Question 13

How many volts and what is the ESD class of:

Damage you can’t feel

Answer 13

ESD Class 0

0-200V

Question 14

How many volts and what is the ESD class of:

Damage you can’t feel

Answer 14

ESD Class 1

200-1,900V

Question 15

How many volts and what is the ESD class of:

Damage you might feel

Answer 15

ESD Class 2

2,000-3,999V

Question 16

How many volts and what is the ESD class of:

Damage you can probably detect as spark with your body?

Answer 16

ESD Class 3

4,000-15,000V

Question 17

How many types of ESD damage can occur to electronic devices and what are they?

Answer 17

3 Classes

Upset, Latent Defect, Catastrophic

Question 18

What is the name for the lowest level of ESD damage and what are its characteristics?

Answer 18

Upset

Most common type. ESD so small that no physical damage occurred.

Damage to the system could materialize into problems to the internal software and programming.

A component may have to have its operating system reloaded, which requires erasing data.

Question 19

What is the name for a medium level of ESD damage and what are its characteristics?

Answer 19

Latent Defect

Could occur without knowledge to the technician, but damage has occurred.

The unit may still pas its self-test or BITE sequences with no indications of problems, but a failure could occur only in a specific flight (use) parameter that may be difficult to duplicate on the ground.

Effect include:

Assembly passes inspection, product passes inspection, works for a while, more returns/losses, warranty costs

Question 20

What is the name for the highest level of ESD damage and what are its characteristics?

Answer 20

Catastrophic Failure

Easiest to discover but it’s the most costly. ESD so severe that boards and chips can no longer operate.

Question 21

What is an ESD foot strap and how must it be worn?

Answer 21

It’s a wrap around the foot and it must be worn underneath the heal as well so that it makes contact with the ground to promote discharge when the wearer walks. This discharges electrical potential to ground.

Question 22

How is an ESD wrist strap used?

Answer 22

It is worn on the wrist and must be worn and then attached to the designated grounding point before working on ESD sensitive components. It also must be tested periodically.

Question 23

What is a grounding point that a technician and work bench can use?

Answer 23

A ring terminal can go on the center screw on an outlet or plug into a the grounding plug port.

Question 24

What are some ESD protective measures a technician should take when working inside a box?

Answer 24

Have a grounded work surface such as a bench, pad and wrist strap with a common ground.

Use protective ESD coverings when a part is not being directly worked on such as storage in an ESD bag or box.

Question 25

What is a method of non-contact ESD protection?

Answer 25

Air ionizer that floods an area with ions that are designed to neutralize negative charges that might exist in the air. This is especially needed in heated super dry air. Ionizers raise the humidity level in the air to 40-70%.

Question 26

What is a protective ESD device that’s rarely used in aviation but may be available in component manufacturing?

Answer 26

Faraday Cage

Question 27

What clothing selection may be helpful when removing aircraft LRUs?

Answer 27

Natural fiber materials rather than synthetic rayon or plastic clothing.

Question 28

What are 8 precautions to be taken when working in ESD sensitive areas?

Answer 28

• Test ESD wrist straps and ESD footwear daily
• Keep wrist strap snug
• ESD food strap under heal to contact the floor
• ESD smocks buttoned up
• Only trained or escorted people allowed in ESD protected area
• Keep work area clean and clear of insulators
• Handle un-packaged ESD sensitive items only when grounded
• Visually check all grounding cords to make sure they are connected.

Question 29

What is a BITE test?

Answer 29

Built-in test equipment (BITE) for avionics primarily refers to passive fault management and diagnosis equipment built into airborne systems to support maintenance processes. Built-in test equipment includes multimeters, oscilloscopes, discharge probes, and frequency generators that are provided as part of the system to enable testing and perform diagnostics.