Factory safetyReading time 11 min
No spark, no warning, and the part is already damaged
About half of all ESD damage is latent, the part survives the line and fails in the field. That kind of defect never traces back.
01Where static comes from
When two materials touch and separate, electrons move from one to the other, triboelectric charging. The triboelectric series sets the direction: skin, glass and nylon tend positive; PTFE, PVC and silicone tend negative.
| Motion | 10 – 20% RH | 65 – 90% RH |
|---|---|---|
| Walking across carpet | 35,000 V | 1,500 V |
| Walking on vinyl flooring | 12,000 V | 250 V |
| Rising from a work chair | 18,000 V | 1,500 V |
| Picking a PE bag off the bench | 20,000 V | 1,200 V |
| Peeling tape off a roll | over 15,000 V | a few thousand V |
02Three discharge models
| Model | Full name | Scenario |
|---|---|---|
| HBM | Human body model | A charged person touches the part. The most common case. |
| MM | Machine model | A charged metal fixture or piece of equipment touches the part |
| CDM | Charged device model | The part itself is charged and touches ground. Extremely fast discharge. |
03EPA: the ESD protected area
The core idea in IEC 61340-5-1 is the ESD protected area, a zone where every conductor, people included, is bonded to the same ground reference so no potential difference exists between them.
- Wrist straps. The primary way to ground a person, with a 1 MΩ resistor in series to limit current. Test them at the start of every shift.
- ESD bench and floor matting. Surface resistance of 10⁶ to 10⁹ Ω, too low is a shock hazard, too high does not dissipate.
- ESD footwear and flooring. How you ground standing or moving operators.
- Ionizers. They handle charge on insulators, plastic housings, tape and packaging cannot be grounded, only neutralized.
- Packaging. Conductive (black), shielding (silver) and dissipative (pink) bags all serve different purposes; only a shielding bag blocks an external field.
04Humidity and environment
Higher relative humidity forms a thin film of moisture on surfaces, raising surface conductivity so charge bleeds away on its own. The usual recommendation for an EPA is 40 to 60% RH:
- Below 30%: static risk climbs sharply.
- Above 70%: metal parts and PCBs risk oxidation and condensation.
05How you prove it works
| Item | Frequency | Tool |
|---|---|---|
| Wrist strap function | Every shift start | Wrist strap tester |
| Bench / floor mat surface resistance | Quarterly | Surface resistance meter |
| Ionizer balance voltage | Quarterly | Charged plate monitor (within ±35 V) |
| EPA ground resistance | Annually | Ground resistance tester |
| Charge on people and tools | Spot checks | Non-contact electrostatic fieldmeter |