First, what is EOS ?
EOS is an abbreviation for Electrical Over Stress , which refers to all excessive electrical stress. When the external current or voltage exceeds the maximum specification of the device, device performance may be impaired or even damaged.
EOS is usually produced in
1. Power (AC/DC) interference, power supply noise, and overvoltage.
2. Transient current / peak / low frequency interference due to test program switching (hot switching) . The duration of the process can be from a few microseconds to a few seconds (and possibly a few nanoseconds), and damage caused by very short EOS pulses is similar to ESD damage.
3. Lightning.
4. Test the transient / glitch / short-time pulse waveform interference caused by the program switch .
5. The test design is poor, for example, sending a test signal to the device if the device has not been powered up or has exceeded its operating limit. For example, add a test signal before powering the device, or exceed the maximum operating conditions.
6. Pulse signal interference from other devices, ie pulses sent from other devices.
7. Inappropriate work steps, the workflow is not very reasonable
8. Ground point bounce (high voltage due to fast current conversion due to insufficient grounding point)
Second, what is ESD ?
ESD is the reduction of the English Electrical Static Discharge , and the Chinese interpretation is electrostatic discharge. The charge is transferred from one object to another. Static electricity is an objective natural phenomenon that occurs in a variety of ways, such as contact, friction, and the like. Static electricity is characterized by high voltage, low power, low current and short duration of action. The body's own actions or contact with other objects, separation, friction or induction can generate static electricity of several thousand volts or even tens of thousands of volts. Static electricity causes serious harm in many areas. Frictional electrification and human body static are two major hazards in the electronics industry. The main measures for electrostatic protection during production are electrostatic leakage, dissipation, neutralization, humidification, masking and grounding. The human body electrostatic protection system mainly consists of anti-static wrist straps, ankle straps, overalls, shoes and socks, caps, gloves or finger sleeves. It has functions such as electrostatic leakage, neutralization and masking. Electrostatic protection work is a long-term system engineering. Any mistake or omission in any link will lead to the failure of static electricity protection work.
Third, the contrast difference
EOS | ESD |
Typically, the power generated by the test equipment and | ESD is a special case of EOS , limited energy , caused by static charge |
The duration of the event is in the microseconds to the second . ( may also be nanoseconds ) | Event duration in picoseconds to nanoseconds |
Damages include metal wire melting, heat generation, high power, latch-up effects | The visibility is not strong and the damage location is not easy to find . |
Short EOS pulse damage looks like ESD damage | It usually causes damage at the transistor level. |
Fourth, static protection
1. Set the electrostatic area
Description : Set the static sensitive area at the production site, and make obvious warnings so that everyone at the scene can pay attention.
2 , precautions in the static area
a. The operator should wear an anti-static wristband, should wear anti-static clothing, shoes, scarves, chairs should be equipped with anti-static sleeves. (One end is in contact with the human body and the other end is connected to the ground wire)
b. It is possible to place an anti-static tablecloth in the area where the PBA is placed , and to connect the anti-static grounding buckle.
c. All items in the electrostatic area should not exceed 100V . The container in the electrostatic area should be made of antistatic material. If the static voltage of the items in the static area exceeds 100V , this should be done by using a deionizing fan to eliminate static electricity on the surface of the object. Note: Items not related to production activities should not be placed in the anti-static area.
3. The ambient humidity should be 50%~60% left
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