The importance of ESD protection
There are two reasons why ESD has been difficult to control in a modern manufacturing environment.
First of all, ESD damages electronic components is completely undetectable. To generate a discharge that can hear a "click" sound requires about 2000V of charge accumulation. The 3000V charge can feel like a small electric shock. Only 5000V can see the spark. . Ordinary circuits such as CMOS or EPROM chips can be damaged by the ESD potentials of 250V and 100V, respectively, and more and more modern circuit devices, including the Pentium processor, can be paralyzed with a potential of 5V.
Second, the main cause of ESD damage actually comes from the normal behavior of the production staff every day. The natural motion friction of the workers at the workbench will form a potential of 400~600V. If they are always in contact with the PCB during the opening or packaging of the foam substrate carton or the bubble plastic bag, the net charge accumulation on the surface of the body may be Approximately 26000V is reached.
Although this is not a problem with ESD itself, if the employees on the production line do not strictly follow the ESD control system, or they use ESD shielding equipment that is faulty, improperly installed or not adequately protected when handling PCBs or components, it will soon appear. problem.
ESD has not received much attention for a long time, but it is one of the common causes of damage to circuit boards and components in electronic assembly. Although most companies use some form of ESD protection, they usually only provide a lower level of protection for damage. Manufacturers always mistakenly believe that they are manufacturing products in a fairly safe environment for ESD. This is not the case.
It is for these reasons that ESD has cost the world's electronics industry billions of dollars each year in terms of yield and early field failure. Therefore, effective ESD protection should be considered as one of the factors critical to product yield and quality, just like any other part of the assembly process.
Recently, ESD equipment manufactured by some suppliers has made progress in networking and protection capabilities, allowing precise control and effective monitoring of ESD. Simply put, it connects the entire production process by connecting ESD protection products into a network, automatically reading important ESD data and analyzing it with a standard PC.
This networked system can discover and record individual ESD events as they occur, as well as find out when and where they occur (such as specific workbench, date, and time) for subsequent research. In addition, as long as the serial number of the failed final product is given, it can link the field failure to the actual ESD event at the time the factory was manufactured.
Although the accuracy of this ESD processing is very high, the networked protection system can't solve all the ESD problems regardless of its capabilities. To truly control it, users need to understand the causes of ESD damage and how to effectively implement protection. For example, what are the elements of a valid ESD solution? What kind of ESD monitoring and protection equipment is available? How can I connect them all to a closed loop system? The answers to these questions can completely end the endless struggle with ESD in the past.
Operators are a major threat to ESD-sensitive electronic components due to frequent access to the defined ESD protection zone (EPA), so anyone in the EPA must wear appropriate clothing such as anti-static shoes, overalls and ankle elastics. Etc. All of these are designed to prevent employees from carrying charge while the plant is moving.
In addition, during assembly and after assembly, PCBs should also be protected from ESD during transport. There are a variety of board packaging products available, including ESD shielding bags, shipping cases and mobile carts.
The primary method of protecting a PCB from ESD hazards is undoubtedly the anti-static wrist strap worn by the operator, which allows the voltage to flow slowly and safely from the operator to the ground through a large electrical resistance (typically 1 MΩ). The problem is that the entire industry does not effectively monitor and control the performance of the operator's wristband. As a result, the method of protecting ESD often does not work at all.
For example, many manufacturers use an automatic tester that allows the operator to insert a wristband into it for testing and then issue proof that they have passed the test. But what we often see is that after the operators go to work, they sign their names directly and leave without testing. Or they fail the test, but they pass the test in an abnormal way (such as using another one). Grasp the slack wristband with bare hands to achieve the desired skin-to-ground contact). Therefore, the traditional wristband test method cannot be traced and is easily misused. It does not let the manufacturer know when his employees have not passed the test, but only know when they passed the test.
There is now an automatic wristband tester that solves these problems. It also doubles as a shoe and garment test. This data acquisition product allows the company's ESD staff to record the results of the wristband test program on the computer with full tracking. Sex. (such as ACL-750, ACL-780 human body static tester)
Although the automatic tester is a big step forward, it is not a completely independent solution to the ESD protection problem. This is because the wristband tester only tests the wristband performance at the test point on the wall, but does not actually touch the product. Test on the side of the workbench.
Another major cause of ESD is the poor grounding of the workbench and tools. Although grounding equipment such as grounding points, work chairs, and ESD dissipating pads keep all items in the EPA at the same potential, grounding can easily be overlooked. Therefore, in order to further implement the ESD protection scheme, a method is needed to continuously monitor the performance of the actual application of the wristband and other ESD facilities in real time. In addition to the standard ESD facilities described above, continuous ESD monitoring equipment (which can be used in ESD products or a separate one) is required. When ESD performance exceeds ESD safety specifications and ESD events occur, it should be automatic. Call the police.
Another advantage of such a device is that it can be quickly discovered if an ESD facility fails. Any ESD protection solution must not only ensure that the training staff understands and understands the ESD, but also regulates their behavior in an ESD-safe manner from beginning to end, while ensuring that all facilities used to protect the ESD actually play their respective roles. We often find that manufacturers are using ESD facilities that are completely ineffective or even useless, and they don't know this at all; similarly, we also find that sometimes manufacturers think their ESD problem is because the facility is faulty, but actually the facility itself works. Normal but not working properly.