I. Principles of Electrostatic Protection

 

1. Prevent the accumulation of static electricity in areas where it is likely to be generated, keeping it within a safe range.

2. Rapidly eliminate and discharge any static electricity that has already accumulated.

 

II. Methods for Electrostatic Protection

 

1. Use of Anti-Static Materials:

Metals are conductors; however, because they allow for high leakage currents, they can damage electronic components. Conversely, insulating materials are prone to generating static electricity through friction. Therefore, neither metals nor insulating materials are suitable as anti-static materials. Instead, "electrostatic conductors"—materials with a surface resistance of less than $1 \times 10^5 \, \Omega\cdot\text{cm}$—and "electrostatic semi-conductors"—materials with a surface resistance between $1 \times 10^5$ and $1 \times 10^8 \, \Omega\cdot\text{cm}$—are used. For example, a common anti-static material is rubber mixed with conductive carbon black, which keeps the surface resistance below $1 \times 10^6 \, \Omega\cdot\text{cm}$.

 

2. Leakage and Grounding:

Ground areas where static electricity may be or has already been generated to provide a discharge path. Establish an "independent" ground connection by burying a grounding wire, ensuring the resistance between the ground wire and the earth is less than $10 \, \Omega$.

 

3. Eliminating Static Electricity from Conductors:

Static electricity on a conductor can be dissipated into the earth through grounding. The voltage of a charged object over time can be expressed by the following equation:

$U_T = U_0 e^{-t/RC}$

Where $U_T$ is the voltage at time $t$ (V), $U_0$ is the initial voltage (V), $R$ is the equivalent resistance ($\Omega$), and $C$ is the equivalent capacitance of the conductor (pF).

Generally, it is required that static electricity be dissipated within 1 second—that is, the voltage must drop to a safe level of below 100 V within 1 second. This prevents damage to sensitive electronic components (such as SSDs) that could otherwise be caused by an excessively rapid discharge or an overly high discharge current. For instance, if $U_0 = 500 \, \text{V}$ and $C = 200 \, \text{pF}$, achieving a voltage ($U_T$) of 100 V within 1 second would require a resistance ($R$) of $1.28 \times 10^9 \, \Omega$. Therefore, electrostatic protection systems typically incorporate a 1MΩ current-limiting resistor to keep the discharge current below 5mA. This is a safety feature designed for operators; should an operator within an electrostatic protection system accidentally come into contact with a 220V industrial power source, the risk of harm is mitigated.

 

4. Eliminating static electricity from non-conductive materials:

Since electric charges cannot flow across insulators, grounding—a common method for dissipating static—is ineffective for such materials. The following measures may be employed instead:

(a) Use ionizers (ion blowers) — These devices generate positive and negative ions that neutralize static charges at the source. They can be positioned within the workspace or near the placement heads of pick-and-place machines.

(b) Use antistatic agents — These are surfactants that can be applied to the surfaces of equipment or objects to rapidly eliminate static electricity.

(c) Control environmental humidity — Increasing humidity enhances the surface conductivity of non-conductive materials, making it more difficult for static charges to accumulate. In dry climates (such as in northern regions), this can be achieved through humidification and proper ventilation.

(d) Implement electrostatic shielding — Equipment prone to generating static electricity can be enclosed in a shielded cover or cage, which must then be effectively grounded.

 

5. Process control methods:

To minimize the generation of static electricity during the manufacturing of electronic products, control the accumulation of static charges, and ensure the rapid dissipation or timely release of any existing static, effective measures must be implemented across various areas—including facility design, equipment installation, operational procedures, and management policies.

 

III. Electrostatic Protection Equipment

 

1. Personal electrostatic protection systems: These include antistatic wrist straps, garments, caps, gloves, footwear, and socks.

2. Antistatic flooring: This includes options such as antistatic terrazzo, antistatic rubber flooring, PVC antistatic plastic flooring, antistatic carpeting, and antistatic raised (access) flooring.

3. Antistatic operational equipment: This includes items such as antistatic workbench mats, antistatic packaging bags, antistatic transport carts, and antistatic soldering irons and tools. IV. Electrostatic Measurement Instruments

 

1. Electrostatic Field Testers: Used to measure the surface resistance of items such as tabletops and flooring. Different specifications of instruments should be selected based on whether the surface is flat or non-flat.

2. Wrist Strap Testers: Used to verify the effectiveness of wrist straps.

3. Personnel Electrostatic Testers: Used to measure the amount of static electricity carried by a person, the impedance between a person’s feet, the potential difference between individuals, and the effectiveness of protective equipment such as wrist straps, grounding plugs, and work garments. They can also serve as an entry-point discharge system to prevent static electricity from being carried into the workspace.

4. Megohmmeters: Used to measure the impedance or resistance of conductive, anti-static, and static-dissipative surfaces.

 

V. Technical Requirements for ESD (Electrostatic Discharge) Control in Electronics Manufacturing

 

1. Grounding resistance for the ESD grounding system: < 10 Ω.

2. Flooring or floor mats: Surface resistance, 10⁵–10¹⁰ Ω; triboelectric (friction-induced) voltage, < 100 V.

3. Walls: Resistance, 5 × 10⁴–10⁹ Ω.

4. Work surfaces or mats: Surface resistance, 10⁶–10⁹ Ω; triboelectric voltage, < 100 V; system resistance to ground, 10⁶–10⁸ Ω.

5. Resistance from the seat of a work chair to its casters: 10⁶–10⁸ Ω.

6. Work garments, caps, and gloves: Triboelectric voltage, < 300 V; shoe soles: triboelectric voltage, < 100 V.

7. Wrist strap connection cable resistance: 1 MΩ; system resistance when wearing a wrist strap: 1–10 MΩ. Heel grounder (shoe strap) system resistance: 0.5 × 10⁵–10⁸ Ω.

8. System resistance from the platform of a material handling cart to its wheels: 10⁶–10⁹ Ω.

9. Material handling equipment (e.g., component bins, totes, PCB racks): Surface resistance, 10³–10⁸ Ω; triboelectric voltage, < 100 V. 10. Frictional voltage for packaging bags and boxes: <100V.

11. Total human body resistance: 10⁶–10⁸ Ω.

 

VI. Anti-Static Measures in Electronic Product Manufacturing and General Requirements for Electrostatic Protected Areas (EPAs)

 

SMT production equipment must be properly grounded; placement machines should utilize a three-phase, five-wire grounding system with an independent ground connection. Flooring, workbench mats, and seating within the production area must meet anti-static requirements. The workshop environment must be maintained at a constant temperature and humidity. Facilities such as anti-static component trays, turnover boxes, PCB racks, transport carts, anti-static packaging materials, wrist straps, and anti-static soldering irons and tools must be provided.

 

・Establish Electrostatic Protected Areas (EPAs) in accordance with anti-static requirements, marked with clear warning signs. Classify work areas into levels 1, 2, and 3 based on the electrostatic sensitivity of the components being handled, and implement specific protective measures for each level:

Level 1 sensitivity: 0–1999V

Level 2 sensitivity: 2000–3999V

Level 3 sensitivity: 4000–15999V

Components with a sensitivity threshold above 16,000V are considered non-electrostatic-sensitive.

 

・Electrostatic Protected Areas (EPAs) should be maintained at a temperature of 23±3°C and a relative humidity of 45–70% RH. Handling of ESD-sensitive devices (SSDs) in environments with a relative humidity below 30% is prohibited.

 

・Regularly measure the surface resistance of flooring, workbenches, turnover boxes, and other surfaces.

 

・Non-production items—such as tableware, tea sets, handbags, wool fabrics, newspapers, or rubber gloves—must not be placed on workbenches within Electrostatic Protected Areas (EPAs).

 

・Personnel must discharge static electricity before entering an anti-static area. Operators are required to wear designated work uniforms, anti-static footwear, and socks. Before beginning any operation, a safety check of anti-static measures must be performed; production may only commence once these checks are successfully passed.・Wear an anti-static wrist strap during operation and verify its functionality daily.

 

・When testing Static-Sensitive Devices (SSDs), remove one unit at a time from its packaging (box, tube, or tray), test it, and then return it to its packaging; do not pile units on the workbench. Devices that fail testing must be returned to storage.

 

・When performing powered tests, follow the correct power-on and power-off sequences: apply power in the order of low voltage → high voltage → signal voltage. Power down in the reverse order. Ensure correct power supply polarity, and do not exceed the rated supply voltage.

 

・Inspectors must be familiar with the specific models and types of SSDs, testing procedures, and the fundamentals of electrostatic discharge (ESD) protection.

 

VII. Requirements for the Transport, Storage, and Use of Static-Sensitive Devices (SSDs)

 

1. SSDs must not be dropped during transport, and they must remain in their original packaging.

2. The relative humidity in the storage area for SSDs should be maintained between 30% and 40% RH.

3. SSDs must be kept in their original packaging during storage; if repackaging is necessary, use anti-static containers.

4. Storage locations for SSDs must be clearly marked with designated anti-static labels.

5. When issuing SSDs, verify the quantity by visual inspection while the devices remain in their original packaging.

6. When performing write, erase, or data protection operations on EPROMs, ensure that the programmer/eraser is properly grounded and wear an anti-static wrist strap.

7. Personnel involved in assembly, soldering, board repair, or debugging must strictly adhere to all ESD protection requirements.

8. Before final packaging, printed circuit boards (PCBs) that have passed testing and inspection should be treated with an ionized air gun to eliminate any accumulated static charge.

 

VIII. Management and Maintenance of Anti-Static Work Areas

 

1. Establish an anti-static management policy and designate specific personnel to oversee it.

2. Maintain a supply of anti-static garments, footwear, and wrist straps for use by visitors or external personnel.

3. Regularly maintain and inspect anti-static equipment to ensure its continued effectiveness.

4. Check the functionality of wrist straps on a weekly (or daily) basis. 5. The grounding properties of table mats and floor mats, as well as the performance of static eliminators, shall be inspected once a month.

6. The anti-static properties of anti-static component racks, printed circuit board (PCB) racks, turnover containers, transport carts, table mats, and floor mats shall be inspected once every six months.