Written by the PRIMEAG engineering team — 10 years fitting out electronics factories and cleanrooms. Updated 09/2026.
Summary: “Anti-static” only means something when it comes with a measured value. This article explains the three basic measurements a factory QA team can carry out in-house — surface resistance, resistance to ground, and person–footwear–floor system resistance — the pass ranges for each type of material under ANSI/ESD S20.20 & IEC 61340-5-1, the instruments you need, and how to record results so that auditors accept them.
1. Three terms that often get confused
| Term | Resistance range | What it means | Examples |
|---|---|---|---|
| Conductive | < 10⁴ Ω (surface < 10⁶ Ω/sq) | Discharges very fast — sometimes too fast, causing a spark | Black carbon bins, copper tape, the bottom layer of a two-layer mat |
| Dissipative | 10⁴ – 10¹¹ Ω (in practice, specify 10⁶–10⁹ Ω) | Controlled discharge — the standard level for surfaces that touch components | Bench tops, the top layer of mats, garments, carbon gloves, floors |
| Insulative | > 10¹¹ Ω | Does not discharge — holds charge; prohibited in the EPA unless essential | Ordinary plastics, PE bags, kV-rated insulating mats, electrical insulating gloves |
A common mistake: buying a 22 kV insulating mat for the EPA in the belief that “insulating means anti-static” — the result is the exact opposite.
2. The three measurements and the instruments you need
(a) Surface / point-to-point resistance (Rtt) — place two 5 lb (2.27 kg) electrodes 25 cm apart on the surface and measure at 10 V (if <10⁶ Ω) or 100 V. Used for mats, benches, floors, bins and trays. Standards: ANSI/ESD S4.1 (worksurfaces), S7.1 (floors), STM11.11 (planar materials).
(b) Resistance to ground (Rtg) — one electrode on the surface, the other lead clipped to the common ground point. It tells you whether the whole chain — “material + ground cord + grounding point + ground” — is continuous. This is the measurement auditors ask about most.
(c) Person–footwear–floor system (S97.1) — an operator wearing ESD footwear stands on the footplate electrode and holds the hand electrode; you measure the total. A good floor with poor footwear shows up immediately in this test.
Instruments: a surface resistance meter with 5 lb electrodes (SL-031, FMX-003) for (a) and (b); a wrist strap / footwear tester (OTS1801D) for daily checks; an electrostatic field meter (Supra 518) to measure charge on insulators and to verify ionizers. A multimeter cannot be used — its test voltage is too low and it has no standard electrodes.
3. Pass ranges by item (values to write into your internal specification)
| Item | Measurement | Pass | Standard | Frequency |
|---|---|---|---|---|
| Bench tops, table mats | Rtg | < 10⁹ Ω (recommended 10⁶–10⁹) | S4.1 | 6 months |
| Floors, floor mats | Rtt, Rtg | < 10⁹ Ω | S7.1 | 12 months + after polishing |
| Person + footwear + floor | System | < 3.5×10⁷ Ω (or <10⁹ Ω when combined with a wrist strap) | S97.1 | Start of shift (tester) |
| Wrist strap + cord | Tester | 0.75 – 35 MΩ | S1.1 | Start of shift |
| ESD garments | Rtt on the fabric | < 10¹¹ Ω (specify 10⁶–10⁹) | STM2.1 | 6 months / after 50 washes |
| Carbon gloves, finger cots | Rtt | 10⁵ – 10⁸ Ω | IEC 61340-4-3 | Every incoming lot |
| ESD bins, trays, Danpla boxes | Rtt | 10⁴ – 10¹¹ Ω (specify 10⁶–10⁹) | S541 | Every incoming lot |
| Shielding bags | Rtt of inner layer + discharge shielding | < 10¹¹ Ω; < 30 nJ (STM11.31) | S541 | Every lot |
| ESD chairs | Rtg (seat → floor) | < 10⁹ Ω | STM12.1 | 6 months |
| Ionizers | Offset balance, discharge time | ±35 V (recommended ±10 V); 1000→100 V < 10 s | STM3.1 | 6 months |
4. Incoming acceptance test procedure (15 minutes per lot)
- Let the material condition for 12 h at shop-floor temperature and humidity (humidity has a strong effect — record the RH in the report; measuring at 30–50 % RH is the most demanding condition).
- Wipe the surface clean with IPA and let it dry.
- Measure Rtt at 3 random points (floors: 5 points per 100 m²); measure Rtg at 1–2 points if the item is already grounded.
- Record: part number, lot, date, RH/temperature, instrument and calibration due date, test voltage, the value at each point, pass/fail conclusion, the person who measured, signature. Keep for 2 years.
- If it fails → quarantine the lot and notify the supplier; PRIMEAG replaces the lot or carries out a comparison measurement on site.
5. Frequently asked questions
We measured 10¹⁰ Ω — is that a pass? Under S20.20 it still passes (<10¹¹), but it is a sign of degradation — new mats and floors should read 10⁶–10⁸. Check the floor finish, the humidity and the cleaning routine.
Should we measure at 10 V or 100 V? Measure at 10 V first; if the reading is >10⁶ Ω, switch to 100 V. Automatic meters do this for you.
How often should the meter be calibrated? Every 12 months; PRIMEAG can send it for calibration on your behalf and keep track of the reminder schedule.
Need a set of test instruments plus a procedure for your QA team? Get in touch via the contact form — PRIMEAG will send a report template and run a one-session training at your factory when the instruments are delivered.