Electrostatic discharge (ESD) damage to PCBA processing

In PCB processing, triboelectrification and electrification of human body often occur. In the process of PCB production, packaging and transportation, as well as processing, debugging and testing of the integrated machine, it is inevitable that the contact friction of the outside world or itself forms a high surface potential. If the operator does not take electrostatic protection measures, the electrostatic potential of the human body can be as high as 1.5~3kV, so whether triboelectric or human static electricity, it will cause damage to electrostatic sensitive electronic devices. According to the mechanics of electrostatic discharge and discharge effect, the electrostatic damage is generally divided into two categories, which is the adsorption of dust caused by electrostatic discharge, and the breakdown of sensitive components caused by electrostatic discharge.

1. Electrostatic adsorption:

SiO2 and polymer materials are widely used in the manufacturing process of semiconductors and semiconductor devices. Due to their high insulation, high static electricity is easy to accumulate in the production process, and it is easy to absorb charged particles in the air, resulting in the breakdown and failure of semiconductor interface. To prevent hazards, the manufacture of semiconductors and semiconductor devices must take place in a clean room. At the same time, the walls, ceiling, floor, operators and all tools and appliances of the clean room should take anti-static measures.

2. Electrostatic breakdown and soft breakdown:

Ultra-large scale integrated circuits have high integration and high input impedance, and the electrostatic damage of these devices is more and more obvious. In particular, metal oxide semiconductor (MOS) devices have a higher probability of electrostatic breakdown.

Now take MOS field effect transistor (MOSFET) as an example to illustrate: the aluminum gate of MOS field effect tube is covered in SiO2 film, and covers the whole channel, because of the good insulation performance of silicon oxide film, the input impedance of the device is as high as 1012Ω or more, when the static charge appears on the aluminum gate, the high impedance of SiO2 film makes it unable to leak. And it builds up on the aluminum grid. At this time, the aluminum gate, SiO2 film and semiconductor channel are equivalent to a plate capacitor, and the thickness of SiO2 film is only 103A, and its voltage resistance value is only 80~100V, while the input capacitance value of field effect tube is only 3pF. Even a trace charge will increase the voltage, and when the voltage exceeds 100V, the SiO2 film will be broken down. Resulting in grid channel communication, device damage. Voltage breakdown, often SiO2 film at individual points in a certain overvoltage dot breakdown, later as long as the lower voltage, that is, a large area of avalanche breakdown, causing permanent failure. Sometimes high voltage static electricity will directly damage the lead in the chip, so that the IC permanent failure.

The damage of electrostatic discharge to electrostatic sensitive devices is as follows:

Hard breakdown. Cause the failure and damage of the whole device at one time.

Soft breakdown. It causes local damage to the device, reduces the technical performance of the device, and leaves hidden dangers that are not easy to be found, so that the device cannot work normally. The damage caused by soft breakdown is sometimes more dangerous than that caused by hard breakdown. In the early stage of soft breakdown, the performance of the device is slightly decreased. In the process of use, as time goes by, the soft breakdown will develop into permanent failure of PCB components and lead to equipment damage.

There are two main reasons for the failure of devices caused by static electricity: the damage caused by electrostatic voltage mainly includes dielectric breakdown, surface breakdown and gas arc discharge; The damage caused by electrostatic power mainly includes thermal secondary breakdown, volume breakdown and metal spraying melting.

In production, the electronic Device that is Sensitive to electrostatic reaction is often called Static Sensitive Device (SSD). This kind of electronic devices mainly refer to very large scale integrated circuits, especially metal oxide film semiconductor (MOS) devices