How Does Static Electricity Hazard Form in the Electronics Industry?
Static electricity hazards in the electronics industry can be divided into two categories: one is the adsorption of airborne dust caused by electrostatic attraction; the other is dielectric breakdown caused by electrostatic discharge.
1. Electrostatic Adsorption
In the manufacturing process of semiconductor components, due to the extensive use of tools and materials made of quartz and polymers, which have high insulation properties, unavoidable friction during use can cause surface charges to accumulate continuously, increasing the potential.
Due to the mechanical effects of static electricity, airborne dust in the workplace can easily adhere to the chip surface under these conditions. Even small dust particles can affect the performance of semiconductor devices. Therefore, the production of electronic products must be carried out in a clean environment, and operators, tools, and the environment must take a series of anti-static measures to prevent and reduce the formation of static electricity hazards.
2. Classification of Dielectric Breakdown
The breakdown of components caused by static electricity is the main form of static electricity hazard in the electronics industry. In a strong electric field, as the field strength increases, charge accumulates. When it reaches a certain level, the dielectric loses its polarization and becomes a conductor, eventually leading to thermal damage. This phenomenon is called dielectric breakdown. Dielectric breakdown can be categorized into three types: thermal breakdown, chemical breakdown, and electrical breakdown.
(1) Thermal Breakdown
When a dielectric is in operation, if the heat generated by energy loss exceeds the heat dissipated to the surrounding environment, the dielectric temperature rises rapidly, increasing conductivity until thermal damage occurs. Therefore, the core issue in thermal breakdown is heat dissipation. Thermal design is a crucial aspect of product design.
(2) Chemical Breakdown
Under high voltage, a strong electric field can cause localized air collision ionization near defects or pores on the dielectric surface or within the dielectric. This ionization causes dielectric glow, generating chemical substances-ozone and carbon dioxide-which reduce insulation performance and lead to dielectric damage.
(3) Electrical Breakdown
Electrical breakdown occurs when a dielectric is subjected to a strong electric field, causing it to emit free electrons. Free electrons increase rapidly with increasing electric field strength, thus destroying the insulating properties of the dielectric. It is evident that electrical breakdown is essentially caused by charge accumulation; therefore, preventing charge accumulation can prevent electrical breakdown.
3. Electrostatic Breakdown and Discharge
(1) Electrostatic Discharge
Although electrostatic discharge and discharge generated by an external stable power supply are both caused by charge accumulation, they have significant differences. First, in the case of electrostatic discharge, the discharge source is space charge, and therefore its stored energy is limited, unlike an external power supply which has the ability to continuously discharge. Thus, it can only provide energy for short-term, localized breakdown. Although the energy of electrostatic discharge is relatively small, its discharge waveform is very complex and difficult to control. Soft breakdown of semiconductor devices is related to this.
(2) Electrostatic Breakdown
Component breakdown damage caused by electrostatic discharge is the most common and serious hazard in the electronics industry, especially in the manufacturing and assembly of electronic products. Electrostatic discharge can cause hard breakdown or soft breakdown of devices. Hard breakdown is a one-time permanent failure of the device, such as an open circuit or short circuit between the device's output and input. Soft breakdown can degrade the performance of components and reduce their specifications, creating potential for failure. Because soft breakdown causes circuits to malfunction intermittently (due to reduced specifications) and is difficult to detect, it causes significant trouble for overall system operation and troubleshooting. During soft breakdown, equipment can still operate with a "fault," its performance not fundamentally changed, and it may pass factory inspection, but it is prone to failure again at any time. Multiple soft breakdowns can lead to hard breakdown, causing abnormal equipment operation, resulting in losses for users, damage to the manufacturer's reputation and product sales, and even irreparable losses to the country.
4. Static Electricity from the Human Body
In industrial production, a major cause of component damage and interference with the normal operation of electronic equipment is electrostatic discharge from the human body. Electrostatic discharge from the human body can cause electric shocks and injuries, and can also trigger secondary accidents (i.e., component damage), therefore, it should be taken seriously. Static electricity is generated by the human body converting the mechanical energy consumed during daily work into electrical energy. The human body is a static conductor. When insulated from the ground (e.g., with shoes made of insulating material), a capacitor is formed between the body and the ground, storing electrical charge. The charging voltage is typically ≤50kV.
A very common and subtle action can generate a considerably high static voltage. When the human body discharges a charged substance, it will react to varying degrees; this reaction is called electric shock sensitivity. While a static shock will not cause major physiological damage, it may affect health or harm the body.
The limit for electric shock injury is 3.0kV. Furthermore, touching static-sensitive devices with a charged body can damage these devices.
III. Anti-static Control Technology (Measures)
Based on the principles, hazards, and laws of electrostatic discharge, the following principles can be followed to establish effective anti-static control measures to prevent harm.
a) Incorporate electrostatic control into the design
b) Prevent the accumulation of electrostatic charge and suppress and reduce the generation of static electricity
c) Establish a fast and safe discharge channel
d) Detect and monitor the effectiveness of anti-static measures
1. Incorporate electrostatic control into the design
(1) Anti-static design of the production environment
The anti-static design of the production environment for electronic products is the key to ESD control. The design is based on the insulating film of electronic components, the electrostatic breakdown voltage of electrostatic sensitive devices (ESDS) in the whole machine, and the anti-static performance of the production equipment. Manufacturers must determine a specific ESD control level, which is determined by the most sensitive components in the production process, and the production environment must ensure the safety of this level. According to DGJ08-83-2000 "Technical Specification for Anti-static Engineering", the engineering design for controlling static electricity is specifically divided into three levels: Level 1 standard is that the absolute value of the electrostatic potential in the control room is not greater than 100V; Level 2 standard is that the absolute value of the electrostatic potential in the control room is not greater than 200V; Level 3 standard is that the absolute value of the electrostatic potential in the control room is not greater than 1000V. The applicable locations for the anti-static engineering classification standards are shown in Table 5 below:
Since static electricity damage is invisible, eliminating ESD hazards requires prevention as the primary approach. Electrostatic protected areas (EPAs) must be set up in the work area. According to IEC 1340-5-1 (1995) "General requirements for protection of electronic devices," the core requirement for EPAs is equipotential bonding, which connects personnel, materials, and work surfaces together and electrically connects them to a common ground to prevent potential differences between different objects. Because ESD does not occur between materials that maintain the same potential or zero potential, ESD-prone devices or circuit boards in an EPA environment are protected from ESD damage.