ESD & Lab Safety

ESD — electrostatic discharge — is the static-electric shock you've felt walking across a carpet and touching a doorknob. To you, it's harmless. To a CMOS chip, a few hundred volts (well below what you can feel) is enough to destroy it. The damage is often invisible and often delayed.

Why it matters

Many of the parts we handle — ESP32 microcontrollers, BME280 sensors, USB-C controllers, anything CMOS — have gate oxides only a few nanometres thick. A spark of static jumps from your finger across those layers and either:

1. Kills the part outright — the part doesn't work when soldered down.
2. Wounds it — the part works at first, gradually drifts out of spec or fails weeks/months later in the field.

The second case is the dangerous one. Wounded parts ship inside customer products. The board passes initial test and then fails in three months on a Lagos rooftop, well after the customer has assumed it just works.

What kills a part

You don't need a visible spark. A static potential of 100 V is enough to damage modern CMOS gates, and 100 V is below the threshold you can feel (which is around 3 kV). So the rule has to be: assume you're charged. Always.

Sources of static at the bench:

• Walking across a carpet, especially in dry weather (hot Harmattan season is the worst).
• Sliding a chair backwards then sitting back down.
• Synthetic clothes (polyester, nylon).
• Sliding a part across a plastic tray.

What the next slide covers

Protection is straightforward — wrist strap, mat, antistatic bag, conscious handling — and the discipline is uniform across the lab whether you're working on a one-off prototype or a thousand-unit production run. Slide 4.2 covers the practical bench setup.

The TL;DR for this slide: ESD damage is invisible, common, and entirely preventable. The rest of the lesson is how to prevent it.

ESD protection is one of those disciplines that feels excessive until you've watched a board die from skipping it. Two pieces of equipment, one habit. That's the whole system.

The three protections, in order

1. The wrist strap (the most important one).

A wrist strap is a conductive band around your wrist, connected through a built-in 1 MΩ resistor to a grounded mat or earth point. The resistor is the key — it limits the discharge current if you accidentally touch live mains, so the strap doesn't electrocute you while keeping you at ground potential for static.

Routine: strap on before you handle any IC. Strap off only when you're not handling parts.

2. The mat.

An ESD mat is a conductive rubber surface on the bench. It's connected to the earth point that your wrist strap also connects to. Parts placed on the mat are at the same potential as the mat (which is at the same potential as you, via the strap). No potential difference → no static discharge.

Rule: parts go on the mat, not on the bench wood next to it. Static-sensitive parts go on the mat the moment they come out of the antistatic bag.

3. Antistatic packaging.

ICs ship in pink antistatic bags (slightly conductive plastic) or static-dissipative tubes. Keep the part in the bag until you're ready to install it. When you're done with a part, put it back in the bag.

The habit: don't slide

When you move a part across the bench, don't slide it. Lift and place. Sliding generates static; lifting doesn't.

Handing a part to someone

The right way: both of you on grounded mats, both wearing wrist straps, hand off above the mat. If they're not at a workstation, walk the part over to their bench inside its antistatic bag. Never hand-off across a bench gap without protection.

The wrong way: throw it, drop it from height, set it on the wood, take it out of the bag prematurely. All of these are how parts die.

The single-sentence summary

Strap on, mat down, bag closed until needed, lift-don't-slide. That's ESD protection in practice.

Soldering is the most physical thing you'll do in this module — and the most dangerous if you're not careful. Iron tips at 350°C, lead-free flux fumes, hot solder spitting if you rush. Each one is manageable; together they need a few habits to handle safely.

Iron temperature

Through-hole soldering runs at 320–380°C depending on the joint mass and the solder. Set your soldering station to this range; don't change it without a reason.

What if it's not hot enough? Use a slightly larger tip, not a higher temperature. The mass of the tip carries the heat. Cranking the temperature up doesn't speed up soldering — it just burns flux faster than it can clean.

What if it's too hot? You'll see flux fume aggressively, hear it sizzle, and the pad may start to discolour. Drop the temperature and let the iron cool.

Ventilation and fume extraction

Solder flux fumes are not good to breathe. Lead-free flux is worse than the old lead-tin flux on that front — the rosin breakdown products irritate eyes and lungs.

Use the fume extractor. A fume extractor is a small box with a fan and a filter cartridge. Position it so the intake is between your face and the joint, about 15 cm above the work. Watch the smoke go into the extractor, not past it.

Open the window if you can. A breeze across the bench doesn't replace the extractor (the fumes still hit your face on the way past) but it helps thin the lab air.

The little injuries to avoid

• Burns. Iron tips are 350°C. Don't grab the wrong end of the iron. Park it in the cradle between joints — never on the bench.
• Solder spit. When you put the iron on a wet joint or a still-warm joint, water (or excess flux) can flash to vapour and spit hot solder. Wear safety glasses. Always.
• Cutting trimmed leads. When you snip excess lead lengths after soldering, the cut piece flies somewhere. Hold the lead with one hand and snip with the other, cupping the cut piece in your palm so it doesn't end up across the room (or in someone's eye).

When to stop

If you feel light-headed, your eyes start watering, or you're getting careless with the iron — stop. Take five minutes off the bench. Soldering done while tired is how the bad joints happen and how injuries happen.