Recently, I have been doing ESD testing of electronic products. From the test results of different products, I found that this ESD is a very important test: if the board design is not good, when the static electricity is introduced, it will cause the product to crash or even the components. Damage. Previously only noticed that ESD would damage components, I did not expect that enough attention should be paid to electronic products.
ESD, also known as Electro-Static discharge. It is known from the learned knowledge that static electricity is a natural phenomenon, usually produced by contact, friction, and induction between electrical appliances. It is characterized by long-term accumulation and high voltage (which can generate static electricity of several thousand volts or even tens of thousands of volts). ), low power, low current and short duration of action. For electronic products, if the ESD design is not designed, it often causes unstable operation or even damage to electronic and electrical products.
There are two methods commonly used in ESD discharge testing: contact discharge and air discharge.
Contact discharge is the direct discharge of the device to be tested; air discharge is also called indirect discharge, which is the coupling of strong magnetic field to the adjacent current loop. The test voltage for these two tests is generally 2KV-8KV, which is different in different regions. Therefore, before designing, we must first understand the market targeted by the product.
The above two cases are basic tests for the human body when the electronic product is in contact with the electronic product due to human charging or other reasons. The chart below shows the air humidity statistics for some regions in different months of the year. It can be seen from the picture that Lasvegas has the least humidity throughout the year, and the electronics in the region should pay special attention to the protection of ESD.
Humidity varies from place to place around the world, but at the same time, in one area, if the air humidity is different, the static electricity generated will be different. The following table is the collected data, from which it can be seen that the static electricity becomes larger as the humidity of the air decreases. This also indirectly indicates the reason why the static spark generated when taking off the sweater is very large in the winter in the north.
Since static electricity is so harmful, how can we protect it? We usually take three steps in the design of static electricity protection: prevent external charge from flowing into the circuit board and cause damage; prevent external magnetic field from damaging the circuit board; prevent electrostatic field generation. Hazard.