Module 5.12-5.14 ESD, software management and the electromagnetic environment

These three sub-modules are practical and are examined for almost every category. They lend themselves to questions on procedures and precautions.

Knowledge levels

Sub-module	A	B3	B1	B2 / B2L
5.12 Electrostatic-sensitive devices	1	1	2	2
5.13 Software management control	—	1	2	2
5.14 Electromagnetic environment (EMC, EMI, HIRF, lightning)	—	1	2	2

5.12 Electrostatic-sensitive devices (ESDS)

The risk

• A person walking on a carpet can build up several thousand volts of static. We feel a discharge only above about 3 000 V, but MOSFETs, CMOS ICs and many microcircuits can be damaged by less than 100 V.
• Damage may be catastrophic (device fails immediately) or latent (weakened device that fails later in service - the most dangerous case because it passes tests).

Identification

• ESDS components and LRUs carry a yellow/black ESD warning label (hand in a triangle with a stroke through it).
• Manuals state ESD precautions in the task.

Protection

Equipment / practice	Purpose
Wrist strap with a series resistor (about 1 MΩ) connected to a ground point	keeps the technician at the same potential as the aircraft/bench; the resistor limits current for personal safety
Conductive or dissipative work mats and floor mats	drain charge slowly
Conductive bags / boxes (metallised shielding bags), pin shorting caps	protect parts in transport and storage
Ionisers, humidity control	reduce charge generation on insulators
Handling	touch only the case or board edges, do not touch pins or connectors, keep protective caps on connectors until installation
Before handling	ground yourself first, then the unit; test wrist straps regularly

Key fact: Never remove an ESD-sensitive LRU or card without first connecting the wrist strap; store it only in the approved conductive packaging.