Anyone who has had a "shock" touching a car door handle knows static electricity. That discharge, which you barely feel, corresponds to a voltage of thousands of volts. For a person it's an annoyance; for a chip with nanometre-scale transistors it can be permanent damage. And the insidious part is that components can be damaged by discharges too weak to be felt.
What an electrostatic discharge is
When two materials touch and separate, some charges move from one to the other. Walking on carpet in rubber shoes, pulling off a synthetic jumper, sliding across an upholstered chair: the body builds up charge. It stays there until it finds a path to an object at a different potential, and then it discharges in an instant. This is known as ESD, electrostatic discharge.
Dry air encourages build-up: in winter, with the heating on and low humidity, shocks are far more frequent than in summer.
How a component gets damaged
A discharge can:
- destroy a junction or an insulating layer outright: the component stops working;
- weaken it: the component works, but with altered parameters, and fails weeks or months later. This is latent damage, the hardest to recognise, because nobody connects it to the moment it happened.
The most sensitive components are those with exposed integrated circuits: memory modules, M.2 SSDs, processors, motherboards, expansion cards, microcontroller modules. A closed power supply or a hard disk in its enclosure is much less vulnerable.
The essential precautions
You don't need a lab. To build or repair a PC at home, a few habits are enough.
- Discharge yourself before touching. Touch an unpainted metal part of the case or another grounded metal object before picking up a component. Repeat it if you get up or walk around.
- Use an antistatic wrist strap. It's cheap: you wear it on your wrist and clip it to a metal part of the case. The cord contains a high-value resistor, normally 1 megohm, which drains charge slowly and prevents sudden discharges.
- Handle components by the edges. Never touch the gold contacts of RAM, the processor pins or the chips.
- Leave components in their bag until it's time to install them. Metallised antistatic bags, silver-grey in colour, act as a shield. Pink or red ones are simply low charge-generating: they don't shield from the outside.
- Choose carefully where to lay boards. Outside the case, a motherboard sits well on its box or on an antistatic mat. The outside of shielding bags can be conductive: don't use it as a surface for a board you're about to power on.
- Work on a suitable surface: wood, laminate or a dissipative mat. Avoid carpet, synthetic fabrics and plastic.
Clothing and environment
A few details reduce the risk considerably:
- avoid wool or synthetic-fibre jumpers while working; cotton generates less charge;
- don't work barefoot on a rug or in rubber shoes on carpet;
- if the air is very dry, a slightly more humid room helps;
- keep ordinary plastic bags, polystyrene and film away from the work surface: they are excellent charge generators.
Case plugged in or unplugged?
This is a common doubt. The safest advice is to unplug it before working: even with the PC off, a connected power supply keeps a standby voltage on the motherboard, and a slipping screwdriver can do damage. With the switch off and the cable out, press the power button for a few seconds to drain any residual charge from the capacitors.
The wrist strap still clips to the metal of the case: the point is to bring body and components to the same potential, so that there's no difference large enough to cause a discharge.
Myths
- "If I don't feel a shock, nothing happened." False: the human perception threshold is much higher than the voltage that can damage a sensitive component.
- "Touching the radiator is enough." Touching it discharges the body at that instant, but walking recharges you. The right reference point is the case you're working on.
- "Modern components are protected." They have protection circuits on their external pins, designed to withstand discharges during normal use. They are not meant to be handled carelessly when removed.
Shipping and storage
To store or ship a component, use its original shielding bag, closed, and rigid packaging. In my work I always keep a few empty shielding bags: they come in handy whenever you remove an SSD or RAM module to set aside.
In short
- Electrostatic discharges can damage chips even if you don't feel them.
- The damage can be immediate or latent, with failures arriving months later.
- Discharge yourself on the case, use a wrist strap and touch components by the edges.
- Silver bags shield; pink ones only limit charge generation.
- Work with the PC unplugged, on a suitable surface, away from synthetic fabrics and plastic.
