The Invisible Threat
A person walking across a vinyl floor on a dry winter day can generate 15,000 volts. Touching a doorknob discharges it with an audible snap. Touch a PCB with that same charge, and you may not feel a thing — but the MOSFET gate oxide rated for 20V maximum just experienced a silent, invisible, catastrophic breakdown.
ESD (Electrostatic Discharge) damage falls into two categories:
Catastrophic failure: The device is destroyed immediately. It won't power up. It fails ICT. Easy to catch — but the board is already scrap.
Latent defect: The device is degraded but still functional. It passes all electrical tests, ships to the customer, and fails three months later in the field. This is the expensive one — warranty claims, field returns, reputation damage.
ANSI/ESD S20.20 is the standard for protecting electronic components from both types of ESD damage. It defines the requirements for an ESD control program: facility grounding, personnel grounding, material handling, packaging, and verification.
Superb's ESD Control System
Our workshop implements a multi-layer ESD protection system:
Layer 1: Facility Grounding
| Element | Specification | Verification |
|---|---|---|
| Flooring | Conductive epoxy with embedded copper grounding grid | Surface resistance: 10⁴–10⁹ Ω, tested quarterly |
| ESD earth | Dedicated ground rod, separate from electrical safety earth | <1> |
| Grounding points | At every workstation, every 3m along walls | Continuity verified monthly |
Layer 2: Workstation Grounding
| Element | Specification | Verification |
|---|---|---|
| Table mats | Conductive (10⁴–10⁹ Ω surface resistance) | Tested monthly |
| Common ground point | All mats in a zone connected to a single ground bus | 1 MΩ current-limiting resistor in each ground cord |
| Shelving and carts | All metal surfaces grounded. Conductive wheels on carts. | Visual check daily |
Layer 3: Personnel Grounding
| Element | Specification | Verification |
|---|---|---|
| Wrist straps | 1 MΩ series resistor (current limiting for operator safety) | Tested DAILY at entry gate |
| Continuous monitors | At each workstation — alarms if resistance >35 MΩ | Real-time |
| Heel grounders | Conductive strap on each shoe, contacting conductive floor | Tested daily at entry gate |
| ESD smocks | Conductive fibers woven into fabric; covers personal clothing | Worn at all times in production |
| Gloves/finger cots | ESD-safe when handling bare boards or components | Single-use |
Layer 4: Ionization
Grounding only works on conductors. Insulators — component bodies, PCB substrates, plastic trays — cannot be grounded because charge cannot flow through them. Ionization solves this: overhead ionizing blowers generate positive and negative ions that neutralize static charges on insulating surfaces.
Ionizers are installed at: - AOI and X-ray inspection stations - Final inspection workstations - Manual assembly stations - Rework stations
Verification: Ionizer balance (±35V maximum offset) and discharge time (<2 seconds="" from="" 1000v="" to="" 100v="">
Layer 5: Material Handling
| Item | ESD Requirement |
|---|---|
| Component storage bins | Conductive (<10⁶> |
| PCB transport trays | Conductive, slotted, with lids |
| PCB racks | Grounded metal or conductive plastic |
| ESD bags | Metalized shielding film — Faraday cage protection |
| Packaging foam | Anti-static (pink) or conductive (black) — NEVER standard polyethylene |
ESD Entry Protocol
Everyone entering the production floor follows the same protocol:
Put on ESD smock
Attach heel grounders to both shoes
Step onto conductive flooring
Test wrist strap at the personnel resistance tester
Green light → enter. Red light → fix and retest.
This applies to operators, engineers, managers, and visitors. No exceptions. The cost of 30 seconds of compliance is infinitely less than the cost of one latent ESD defect.
Why ESD S20.20 Matters for Your Boards
If you're comparing PCBA manufacturers, ask:
Do they have conductive flooring in production areas? Or just wrist straps on regular vinyl tile?
Are wrist straps tested daily or "when someone remembers"?
Do they have continuous monitors at workstations, or just a once-a-day test?
Are ionizers installed and verified, or are they relying on grounding alone?
Do they use ESD-safe packaging for finished boards, or whatever box is available?
The answers tell you how seriously they take ESD. A manufacturer with a weak ESD program is shipping boards with latent defects you'll discover months later. A manufacturer with a strong ESD program ships boards that work reliably for their designed lifetime.
At Superb, we treat ESD protection as foundational — not optional, not premium, not negotiable.
