Static electricity

As you know, static electricity occurs when two non-conductive objects rub against each other, and its importance in industrial environments is well known. Generally, in workshops and factories that work on electronic boards, Static electricity is of particular importance because static electricity on electronic boards can create high voltages that can damage sensitive components on the board, such as ICs, because the wiring  The interior of some integrated circuits is very sensitive and the smallest voltage can cause them to be destroyed. This issue is also significant in gate MOSFETs because if an electrical load is applied to the gate, a high voltage is created and the MOSFETs are destroyed. It is believed that this issue increases the rate of board rejection by the quality control unit. On the other hand, if static electricity chooses the path of the assembler's body for discharge, it will cause an unpleasant sensation in the person's body.

  To keep the residual voltage for the production line location at a safe voltage level, the total resistance connected to the ground system should not exceed 10 megaohms, which is based on the human body capacitive resistance model and the RC time constant and the total time considered. Taken, it takes 2 seconds to reach a stable value (10 volts) and discharge static electricity. The 2 second time is considered the maximum time for personnel contact.

To limit the current generated for static discharge, the minimum resistance of the discharge path from the wristband, leg strap, ESD protected footrest, and ESD protected tabletop must be at least 1 megaohm. Also, if the above items are It was connected in series to the ground bus, the total resistance of the connected ground bus should be less than 10 megaohms.

In order to control the conditions, it is necessary to perform tests and even install equipment for this purpose, among the main Tests that are performed with the aim of controlling and monitoring conditions include testing the performance of antistatic flooring, testing the grounding system, and testing the connection between the grounding system and the flooring. It is also possible to install equipment that monitors The performance of static discharge systems will be discussed. In the following, in two sections, a brief introduction to static discharge systems and systems for monitoring performance and measuring static electricity will be discussed.