1.When conducting any test, the first thing we need to understand is what the test is? Let's see what is electrostatic discharge?
Electrostatic discharge, commonly abbreviated as ESD, refers to the transfer of electrostatic charges between two objects with different electrostatic potentials due to direct contact or electrostatic field induction. After the energy of electrostatic field reaches a certain level, the phenomenon of discharge through the medium is electrostatic discharge.
Common static discharge phenomena in daily life: During dry seasons such as winter, when we turn off the lights and take off clothes to sleep at night, we often hear crackling sounds and sometimes we can even see small sparks. Accidentally touching someone else's finger or touching a metal handle when opening a door, you will feel electric.
There is static electricity when touching the door handle
2. After understanding the above, let's see why we need to conduct an ESD (electrostatic discharge) test?
Electrostatic discharge may cause changes in the electric and magnetic fields, leading to equipment malfunctions, and may also cause damage to semiconductor devices through energy exchange. So, the test aims to detect the electrostatic discharge immunity of EUT by simulating the discharge of the operator or object in contact with EUT.
Typical semiconductor
Some friends may not fully understand immunity.
Immunity refers to the ability of a device, equipment, or system which can still operate without degrading performance when facing electromagnetic interference. For example, when the mobile phone suffers from electrostatic, still it can keep making calls, sending messages, surfing the internet and other normal functions, then we can say that the mobile phone has good immunity to electrostatic. On the contrary, if the phone has no signal or other functional abnormalities after being exposed to electrostatic, then we can judge that the electrostatic immunity of the phone is not qualified.
3. After understanding the purpose of ESD test, how do we carry out the test?
Let's take medical equipment as an example. There is a corresponding standard YY0505 in the industry, which specifies how we should conduct experiments, what equipment is needed for the experiment, the preparation work before the experiment, the experimental steps, and the content that should be included in the experimental report. In other words, we have a standard for reference. The electrostatic discharge test in the EMC (electromagnetic compatibility) test of medical devices is mainly based on YY0505 and GB17626.2.
4. What equipment required for electrostatic discharge test?
ESD Simulator
Insulated table
HCP & VCP
GRP (ground reference plane)
ESD table
Test site and equipment
5. Electrostatic discharge experimental environment
The laboratory climatic conditions and electromagnetic reference environment: The climate conditions should meet the atmospheric pressure range of 86kpa to 106kpa, the ambient temperature of 15℃ to 35℃, and the relative humidity of 30% to 60%. The electromagnetic environment should be able to ensure the normal operation of EUT equipment without affecting the test results. (There is currently no consensus in the industry on how to determine whether it affects this. In my opinion, if the electromagnetic environment is in a controlled state, we can consider it unaffected. For example, if there is no radio transmission center, each equipment has an EMC certificate from the factory.)
Condition of temperature and humidity
6. ESD test result, the evaluation results are divided into the following four categories.
- Normal performance within the technical scope specified by the manufacturer or user.
- Function or performance is temporarily reduced, but the EUT can recover on its own after the harassment stops, without the need for operator intervention.
- Temporary loss of function or performance, but require operator intervention to return to normal.
- Reduction or loss of function that cannot return to normal state due to hardware or software damage or data loss.
Since the equipment is non-life support equipment, the first two items' results are acceptable and the rest items are unacceptable. That is, if the results are the first two items, then considered qualified, otherwise is unqualified.
