February 11, 2020
Mechanism of electrostatic breakdown
Electrostatic discharge and their damages (from electrostatic breakdown) are a major problem for industrial manufacturing processes. Not only it can damage the production and machines, it also endangers workers.
That is why we have been covering this topic through several articles to explain how we can support factories (especially for the electronics industry) in preventing ESD from happening:
- Static electricity:
- Measures against static electricity:
- Our solutions for ESD prevention:
- Case Study of an installation: Manufacturing of car audio system
To complete this sequence of articles, today we will explain the mechanism of electrostatic breakdown in the electronics industry.
Electrostatic breakdown is a phenomenon in which electronic components such as integrated circuits (ICs) are destroyed by static electricity. Damages by static electricity occur due to high voltage temporarily flowing through the ICs coming from an electrostatic discharge.
When ESD happens, a thin film (insulating layer) such as highly insulating silicon oxide is broken on the ICs. Therefore, the circuit inside is destroyed.
In recent years, electronic components have become lighter and smaller. Therefore, their sensitivity to static electricity has also increased.
In particular, metal–oxide–semiconductor (MOS) lose their function as semiconductors when only a voltage of about 80 to 100 V is applied.
To give an indication, we feel the electrostatic shock being painful when the voltage is about 3 kV. This gives you an idea of how small the voltage is and still damages the production of semiconductors. In fact, in some cases, such as when the oxide film is incomplete, it can be destroyed at lower voltages.
Nowadays, as semiconductor devices become finer and more complex circuits, the wiring spacing (the size of the elements themselves) also becomes smaller. So their electrostatic resistance becomes lower. That is why more sophisticated measures for managing static electricity are required from manufacturers.
Here are some examples of common damages due to electrostatic breakdown from electrostatic discharge, related to the semiconductors:
- When peeling off wafer rack: due to exfoliation charging that occurs during wafer transfer and removal from the wafer rack.
- When peeling the protective film from the substrate: due to peeling electrification that occurs when a protective film is peeled from a liquid crystal glass substrate.
- Sheet peeling during chip mounting: due to peeling electrification that occurs when chips are picked from a wafer sheet.
Charged objects that cause electrostatic breakdown
Workers, equipment, and the semiconductor element itself can be considered as charged objects that cause electrostatic breakdown.
In order to implement the correct solution to prevent ESD, there are 3 existing ESD test models:
- The Human Body Model (HBM): When a charged worker carelessly brings a finger close to a semiconductor element, electrostatic discharge occurs between a terminal of the element and the finger. (Because humans move around and perform various tasks, they are extremely easily charged.)
- The Machine Model (MM): The device is charged when the device comes into contact with the charged conductor. And the device is grounded, causing electrostatic breakdown.
- The Charge Device Model (CDM): The circuit of a semiconductor device is charged, and is discharged when a terminal of the device approaches a nearby conductor, causing electrostatic breakdown in an internal circuit.
1. Human body charging model (HBM)
The device is charged due to discharge when an electrostatically charged person touches the lead of the device. And when the device is grounded, a discharge current flows through the circuit, causing electrostatic breakdown.
In this way, the discharge model from the external electrostatic charge to the semiconductor device is called the “human body charge model”.
The amount of charge released from the charged human body is large, and the discharge energy is extremely large compared to the case of insulator.
2. Machine model (MM)
If the electrostatically charged object is a device, it is called a “machine model”.
If the equipment used in the manufacturing process is not grounded, the conductors will also become charged. Then, when the charged body touches the external terminal of the semiconductor device, electric current penetrates through the device and causes electrostatic breakdown.
3. Charged device model (CDM)
Even if human body models and machine models are adequately protected against static electricity, there is a possibility that ESD induced destruction will occur during the production and assembly of semiconductor devices.
This is due to electrostatic discharge damage when the device itself is charged, and is called “device charging model”.
In this discharge model, the device itself is charged by friction on the surface of the semiconductor device. As a result, conductors such as circuits and leads cause electrostatic induction by an external electric field. In this state, if the lead is grounded, the internal electric field will change abruptly and the discharge current will flow, causing electrostatic breakdown.
How can IKEUCHI help?
As mentioned, electronics components are becoming smaller and smaller. Therefore, more sophisticated measures are required to help manufacturers preventing electrostatic breakdown damages on their production.
That is why, as “the Fog Engineers” we’ve studied the optimal solution to prevent electrostatic discharge (ESD), by adding humidity in working environment. Our none-wetting Dry Fog humidifier offers the adequate solution for sensitive working stations.
Contact one of our engineers to assess the optimal solution to prevent ESD in your production site.
Nina MONCEAUX – IKEUCHI EUROPE B.V.