CDM electrostatic protection principle, ESD electrostatic discharge protection principle

The electrostatic generator is mainly used to generate static electricity, and the output is usually a single polarity, such as positive or negative polarity, and the output voltage can be adjusted, which is usually used in scientific research, electrostatic applications such as electrostatic precipitation, electrostatic spraying, generating electrostatic fields for biological effect research and other places where static electricity is to be applied. When selecting an electrostatic generator, consider the output voltage, polarity, output current, and accuracy. In general, the polarity of an electrostatic generator should be selected according to the electrostatic characteristics of the material, for example, in the case of thin-film products, a negative polarity electrostatic generator is required.

Now it has been widely used in film positioning, film adsorption, steel plate production, wood board production, plastic plate production, material lamination, glass production, label bonding and other industrial fields. If you want to know more about electrostatic generators, Beijing Airlida welcomes you

1. HBM: the discharge mode of the charged human body.

Because the human body will be in contact with various objects and friction, and in contact with components, the human body is prone to static electricity, and it is easy to cause electrostatic damage to components. It is generally believed that most of the electrostatic damage of components is caused by human static electricity. The electrostatic human body can be equivalent to an equivalent circuit in the diagram, which is also known as the human body model.

2. CMD: the discharge model of the charging device.

In the process of component assembly, transfer, testing, testing, transportation and storage, the shell will be electrostatic due to the friction between the shell and other materials. Once the component leads to ground, the housing will be discharged to ground through the core and lead-out legs. This form of discharge can be used using the so-called charged-device model

model, CDM).

3. mm: the discharge mode of the live machine.

Machines can also be charged due to friction or induction. Electrified machines can also cause damage when discharged through electronic components.

4. It does not mean that this item encounters the maximum value of static electricity.

Through the study of the main electrostatic electricity and the actual electrostatic discharge process, it is believed that there are three main modes that cause damage to components, namely the electrostatic discharge mode of the charged human body, the discharge mode of the charged machine and the discharge mode of the charged device.

Discharge mode (HBM) of a charged human body

Discharge mode (mm) of a live machine

Discharge model (CDM) of a charged device

The sensitivity level of electrostatic sensitive devices is classified according to the three modes of HBM, MM and CDM, and generally speaking, there is no necessary relationship between the three modes of the electrostatic sensitive voltage of the device.

Unless otherwise specified, the human body model is used to describe the problems related to the electrostatic sensitive voltage of the device.

The rating of electrostatic sensitive components is determined by the sensitivity level of the most sensitive devices installed on them.

With the continuous development of electronic technology and production process, the harm of electrostatic discharge of MM and CDM types to devices is becoming more and more common, so the method of using MM and CDM modes for analysis has gradually developed.

Common electrostatic discharge modes:

1.HBM, human body discharge model, that is, the charged human body discharges the device, resulting in damage to the device. The discharge path is: human body - device - ground.

2 mm, machine model, i.e. a live device discharges the device, resulting in damage to the device. The discharge path is: machine - device - ground.

3 CDM, charged device model, i.e., the charged device is discharged directly against the enemy. The discharge path is: device - ground.

4 FICDM, inductive discharge model, i.e., the device is discharged after inductive charge. Route: Electric field - device charged - ground.

Human Body Model:

This model characterizes the discharge of a charged contact device in the human body, with Rb being the equivalent human resistance and Cb being the equivalent human capacitance. The equivalent circuit is shown in the figure below. The ESD levels of the HBM model of the device are also given.

Equivalent circuit diagram of the ESD mannequin and its ESD rating.

machine model

The equivalent circuit of the machine model is similar to that of the human body model, but the equivalent capacitance (CB) is 200pf and the equivalent resistance is 0, the difference between the machine model and the human body model is larger, in fact, the storage capacitance of the machine varies greatly, but for the unity of description, 200pf is taken. Since there is no resistance when the machine model is discharged, and the storage capacitance is greater than that of the human body model, the damage to the device at the same voltage is much larger than that of the human body model.

Equivalent circuit diagram of the ESD machine model and its ESD class.

charged device model:

There are three main types of packaging for semiconductor devices (metal, ceramic, and plastic). In the process of assembly, transmission, testing, testing, transportation and storage, the tube shell will be charged because the tube shell rubs against other insulating materials (such as plastic bags for packaging, plastic containers for transmission, etc.). The device itself acts as a plate of a capacitor to store charge.

The CDM model is based on the failure of the device caused by the ground discharge when the charged device is in contact with the ground through the pins, and the device charge model is as follows:

Equivalent circuit diagram of the ESD charging device model and its ESD class.

The ESD level of the device is generally tested according to the above three models, and most ESD-sensitive device manuals have the ESD data of the device, which is generally given as HBM and mm.

The ESD characteristics of the device can be understood through the ESD data of the device, but it should be noted that the ESD characteristics of each pin of the device are quite different, and the ESD voltage of some pins will be particularly low, generally speaking, the ESD voltage of high-speed ports, high-impedance input ports, and analog ports will be relatively low.

There are two components of ESD protection, one is made of silicon-based materials and the other is made of polymer materials!

The working principle is not the same!

The principle of silicon-based materials is similar to that of TVS tubes! Clamp the high voltage first, and then discharge the ground!