Static damage to the principle of PCB board analysis and how to eliminate the hidden danger of static electricity

When it comes to electronic products such as PCB boards, if there is no problem in the development technology, once the failure, most of them are related to static electricity. As we all know, static electricity is everywhere, for some tiny electronic components, as long as the electrostatic breakdown, then the entire production line will also face collapse.

The basic physical properties of static electricity are the following three: attraction or repulsion, a potential difference with the earth, will generate a discharge current. These three characteristics of the impact on electronic components.

1. Static electricity attracts dust and reduces the insulation resistance of components, thus shortening component life.
2. Electrostatic discharge or current generated by heat, so that components are potentially damaged.
3. Electrostatic discharge produces a large amplitude and extremely wide spectrum of electromagnetic fields, causing interference and even damage to electronic components.
4. Electrostatic discharge damage, so that the components are damaged can not work.

It can be seen that electrostatic hazards are incalculable, companies should do a good job of comprehensive protection to prevent losses caused by electrostatic hazards.

ESD hazards to the chip computer consist of boards, and today's boards are mostly manufactured using MOS technology, and their circuits are quite sensitive to electrostatic high voltage. When a person or object with static electricity touches these devices, electrostatic discharge (ESD) will be generated. When the electrostatic high voltage impacts the MOS circuit, its internal oxide film will be broken, destruction, resulting in electrical parts on the spot being damaged or working improperly. Of course, the general electrostatic discharge of the device does not immediately fail, which is the reason most people do not pay attention to ESD.
Static electricity is everywhere in daily life, the practice has proved that people can feel static electricity at least 3.5kV or more, and can hear the sound of static electricity to be more than 4.5k, as for the flash of static electricity on the sweater is to reach more than 5kV.
In addition to the above ESD direct damage to the device, ESD will also induce the MOS circuit internal locking effect (or called parasitic SCR effect), the result is a large increase in MOS internal current, internal logic function failure, resulting in the so-called locking effect. Once the MOS circuit is in a locked state, as long as the power supply is not cut off, the circuit will always be deadlocked, For a long time there can be a burned circuit or degrade the performance of the circuit. For example: when plugging the printer connector with power leads to computer abnormalities (the mouse can not move, the printer alarm), the first remedy is to immediately shut down the computer.

To this end, international organizations have developed a corresponding standard, the ESD caused by electrical failure is divided into the following categories: 

•  Operation ESD failure operating a computer with static electricity, when he touches the computer's exterior such as the keyboard, mouse, and reset button, it is possible that the following computer failure is caused by ESD: computer restart, pause, crash, and other abnormalities, the light need to reset or reinstall a software, the heavy need to replace the hardware.
• Maintenance ESD failure of the person operating the computer with static electricity, and he touched the internal metal conductive parts of the chassis. For example, hand molding internal boards and cards will cause the above-mentioned failure.
• Maintenance ESD failure of the person operating the computer with static electricity, and touching the computer's CPU, board, and other ESD that occurs will cause damage to the parts.