Why do ESD problems in semiconductor factories always start with the "desk mat"?
In the safety management system of semiconductor factories, ESD (electrostatic discharge) may seem invisible, but it is a frequent, easily overlooked, and extremely costly hidden danger. More importantly, the vast majority of ESD failures are directly related to the "anti-static rubber mat/desk mat." Yes, not the machine, not the personnel, not the process… but the material on the surface you touch every day.
I. Why do ESD anomalies always start with the "desk mat"?
You may have seen these scenarios: a wristband is working properly, yet an electrostatic alarm still sounds; grounding is normal, yet the tester occasionally breaks down; personnel are operating according to regulations, yet yield drops; the equipment hasn't been moved, yet the electrostatic sensor is flashing red. Many safety officers' initial reaction is to check the equipment, the grounding wire, and the personnel's operation. But the real root cause is often: aging of the anti-static rubber mat, parameter drift, surface contamination, or corrosion by chemicals leading to uncontrolled resistance. This is because the anti-static mat is a material with extremely high contact frequency throughout the entire operation chain.
It serves the following purposes:
1. Tooling placement
2. Temporary placement of batches of wafers
3. Protection against product contact
4. Friction on the bottom surface of testing equipment
5. Static electricity discharge contacts
If the stage mat malfunctions, all other ESD control measures will fail. It's like a highway with a cracked foundation; even the best car won't be able to drive steadily.
II. Why are anti-static mats prone to "potential failure"?
"Potential failure" is the most troublesome situation for safety officers in the semiconductor industry. Anti-static mats are precisely one of the materials most prone to potential failure, for three reasons:
1. Chemical corrosion causes sudden changes in resistance. The semiconductor industry uses a large number of chemicals: developers, cleaning agents, IPA, etching solutions, etc. When these chemicals fall onto the surface of the anti-static stage mat, they will:
① Damage the thin ESD layer on the stage mat surface
② Form an insulating contamination film
③ Accelerate material aging and degradation
The result is: the stage mat looks fine, but the parameters have completely drifted.
2. Surface Cleaner Residue Affects Dissipation Performance
Many work teams overuse strong degreasers or silicone-containing cleaners to maintain a "visually clean" appearance. These residues can lead to:
① Prolonged static decay time
② Uneven charge accumulation
③ The creation of "instantaneous discharge points"
These types of failures are very insidious but extremely likely to damage sensitive components.
3. Aging Causes Volume Resistivity to Soar from 10⁸Ω to 10¹²Ω
Antistatic rubber mats are polymer materials. Prolonged exposure to:
① Temperature changes
② Ultraviolet radiation
③ Friction
④ Corrosion
All of these will cause the resistance value to increase. A typical example is: "The mat looks usable, but the resistance is far beyond the national standard range."
III. What are the specific requirements of various standards for antistatic mats?
Safety officers most frequently encounter standards including: *SJ/T 10694-2022 Electrostatic Discharge Protection Test Methods for Electronic Product Manufacturing and Application Systems*, *ANSI ESD S20.20-2021 ESD Control System for Electrostatic Discharge Protection*, and *IEC 51345-5-1-2024 Electrostatic Discharge Protection for Electronic Devices - General Requirements*. In addition, my country has various national and industry standards, such as Chinese military standards and industry standards from the Ministry of Ordnance Industry, which will not be elaborated upon due to confidentiality requirements. The requirements of different standards are summarized, stipulating that antistatic table mats/rubber materials must be tested for:
① Point-to-point resistance
② Point-to-ground resistance
This is the basis for judging whether a table mat is qualified.
Furthermore, it is recommended to combine the electrostatic discharge decay time and triboelectric voltage parameters, as these are important parameters for calculating electrostatic discharge energy.
It also clearly stipulates:
① The resistance of the anti-static mat must be kept within 1*10⁹ Ω;
② Prevent sudden discharge and spark discharge;
③ Prevent charge accumulation.
These requirements are to avoid "uncontrolled discharge," which is the risk that semiconductor manufacturers fear most.