How does esd damage

Logic devices are not the only devices requiring anti static precautions to be taken. Even ordinary bipolar transistors can be damaged by potentials of around V. This is particularly true of the newer transistors which are likely to have much smaller internal geometries to give higher operating frequencies.

This is only a broad indication of a very few of the ESD susceptibility levels. However it indicates that all semiconductor devices should be treated as static sensitive devices, SSD. It is not only semiconductor devices that are being treated as SSDs these days.

In some areas even passive components are starting to be treated as static sensitive. With the trend to miniaturisation individual electronics components are becoming much smaller. This makes them more sensitive to the effects of damage from ESD.

The effects of electrostatic discharge, ESD, are dependent on a large number of variables. Most of these are difficult to quantify. The level of static which is built up varies according to the materials involved, the humidity of the day, and even the size of the person has an effect. Each person represents a capacitor on which charge is held. The average person represents a capacitor of about pF but this will vary greatly from one person to the next. The way in which the discharge takes place also varies.

Often the charge will be dissipated very quickly: typically in less than a hundred nanoseconds. During this time the peak current can rise to as much as twenty or thirty amps. The peak current and the time for the discharge are dependent upon a wide variety of factors. However if a metal object is used, like a pair of tweezers or thin nosed pliers the current peak is higher and reached in a shorter time than if the discharge takes place through a finger.

This is because the metal provides a much lower resistance path for the discharge. However whatever the means of the discharge, the same amount of charge will be dissipated. In order to combat ESD and to prevent damage resulting it is necessary to look at the different scenarios that may occur and to characterise them. These scenarios will exhibit different levels of voltage build up, different charge levels, and different discharge characteristics.

Currently there are a number of methods for rating integrated circuits for ESD performance within the manufacturing environment. This charge may be transferred from the material, creating an electrostatic discharge or ESD event. Additional factors, such as the resistance of the actual discharge circuit and the contact resistance at the interface between contacting surfaces, also affect the actual charge that is released.

Typical charge generation scenarios and the resulting voltage levels are shown in Table 1. Also, the contribution of humidity to reducing charge accumulation is shown.

However, it should be noted that static charge generation still occurs even at high relative humidity. An electrostatic charge may also be created on the material in other ways, such as by induction, ion bombardment, or contact with another charged object.

However, triboelectric charging is the most common. When two materials contact and separate, the polarity and magnitude of the charge are indicated by the materials' positions in a triboelectric series. The triboelectric series tables show how charges are generated on various materials. When two materials contact and separate, the one nearer the top of the series takes on a positive charge, the other a negative charge. Materials further apart on the table typically generate a higher charge than ones closer together.

These tables, however, should only be used as a general guide because there are many variables involved that cannot be controlled well enough to ensure repeatability. A typical triboelectric series is shown in Table 2. Virtually all materials, including water and dirt particles in the air, can be triboelectrically charged.

How much charge is generated, where that charge goes, and how quickly, are functions of the material's physical, chemical, and electrical characteristics. A material that prevents or limits the flow of electrons across its surface or through its volume, due to having an extremely high electrical resistance, is called an insulative material. A considerable amount of charge can be generated on the surface of an insulator.

Since an insulative material does not readily allow the flow of electrons, both positive and negative charges can reside on an insulative surface at the same time, although at different locations. The excess electrons at the negatively charged spot might be sufficient to. However, electrons cannot easily flow across the insulative material's surface, and both charges may remain in place for a very long time. A material that allows electrons to flow easily across its surface or through its volume is called a conductive material.

When a conductive material becomes charged, the charge the deficiency or excess of electrons will be uniformly distributed across the surface of the material. If the charged conductive material makes contact with another conductive material, the electrons will be shared between the materials quite easily.

If the second conductor is attached to AC equipment ground or any other grounding point, the electrons will flow to ground, and the excess charge on the conductor will be neutralized. Electrostatic charge can be created triboelectrically on conductors the same way it is created on insulators.

As long as the conductor is isolated from other conductors or ground, the static charge will remain on the conductor. If the conductor is grounded, the charge will easily go to ground. Or, if the charged conductor contacts another conductor of different electrical potential, the charge will flow between the two conductors.

Dissipative materials have an electrical resistance between insulative and conductive materials. There can be electron flow across or through the dissipative material, but it is controlled by the surface resistance or volume resistance of the material. As with the other two types of materials, a charge can be generated triboelectrically on static dissipative material.

However, like the conductive material, the static dissipative material will allow the transfer of charge to ground or other conductive objects. The transfer of charge from a static dissipative material will generally take longer than from a conductive material of equivalent size.

Charge transfers from static dissipative materials are significantly faster than from insulators and slower than from conductive material. Charged materials also have an electrostatic field and lines of force associated with them.

Conductive objects brought into the vicinity of this electric field will be polarized by a process known as induction. See Figure 4. A negative electric field will repel electrons on the surface of the conducting item that is exposed to the field. A positive electric field will attract electrons near the surface, thus leaving other areas positively charged.

No change in the actual charge on the item will occur in polarization. Knowledge Base Search. Log in. Options Help Chat with a consultant. Include archived documents. This content has been archived , and is no longer maintained by Indiana University. If you run a business that deals with lots of sensitive equipment, a grounding mat, and even a grounding table is also highly recommended. If the computer no longer boots after working inside of it, try the below recommendations.

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