How to prevent static electricity hazard ？

This article describes, in order to effectively fight and prevent electrostatic discharge (ESD, electrostatic discharge), must be the right way to use the correct equipment. Due to a series of powerful closed loop ESD prevention, monitoring and ion devices, ESD can now be seen as a process control problem.

Electrostatic discharge (ESD) is the source of the electronic circuit board assembly and component damage a familiar and underestimated. It affects every manufacturer, without any of its size. Although many people think they are producing products in ESD safe environment, but in fact, ESD-related damage continues to the world electronics manufacturing industry has brought billions of dollars per year cost.

What exactly is ESD? Electrostatic discharge (ESD) is defined as, to or from the original has been static (fixed) charge (electron deficiency or excess) discharge (electron flow). Charge under two conditions are stable:

1. When it is "trapped" on a conductive but electrically insulating objects, such as metal, plastic handle screwdriver. 2. When it is to stay in an insulating surface (such as plastics), not in the above flow.

However, if charged with a sufficiently high electrical insulation of the conductor (screwdriver) and close to the contrary potential of the integrated circuit (IC), the charge "jumper", causing electrostatic discharge (ESD).

ESD occurs very rapidly at very high intensity, usually will produce enough heat to melt the internal circuit of the semiconductor chip, the electron microscope look like bullet holes blown out of the boy, causing immediate and irreversible damage. More serious is that this harm is only one tenth of a bad situation at the end of the test to cause failure of the entire component. The other 90% of cases, ESD damage caused by downgrade only partial - meaning corrupted elements may be unaware of the adoption of the final test, but only premature field failures after shipping to customers. As a result, most of the damage the reputation of a local manufacturer to correct any manufacturing defects most pay the price.

However, the main difficulty controlling ESD is that it is not visible, but can reach the point of damaging the electronic components. Produce can hear the "tick" sound of the discharge need to accumulate quite a large charge of approximately 2000 volts, and 3000V can feel a small electric shock, 5000 volts can see the sparks.

For example, such as complementary metal oxide semiconductor (CMOS, complementary metal oxide semiconductor) or electrically programmable read-only memory (EPROM, electricall programmable read-only memory) these common elements, the difference were only 250 volts and 100 volts of ESD potential of the destruction, but more and more sensitive modern elements, including the Pentium processor, as long as 5 volts can be destroyed.

The problem is complex with daily activities causing damage. For example, from the factory floor through the vinyl, between the floor surface and the friction shoes. The result is a pure object charge accumulation of 3 to 2,000 volts of charge, depending on local air humidity considerably.

Even workers in the natural friction of the mobile station is formed can produce 400 to 6000 volts. If during PCB open or packaging foam box or bubble bag, workers have been handling the insulator, then the worker body surface accumulated net charge could reach about 26,000 volts.

Thus, as the main ESD hazards source, all staff into the electrostatic protected areas (EPA, electrostatic protected area) must be grounded to prevent any charge accumulation, and all surfaces should be grounded to maintain everything the same potential in preventing ESD occurs.

To prevent ESD's main product is a bowl with (wristband), there Curly corduroy and dissipative surface or litter - both of which must be properly grounded. Additional aids such as dissipative footwear or heel strap and appropriate clothing are designed to prevent personnel (EPA) and moving the accumulated net charge in the holding electrostatic protection areas.

During and after the assembly, PCB should also prevent ESD from both internal and outer transport. There are many circuit board packaging products can be used in this regard, including shielding bags, shipping boxes and moving carts. While proper use of the device will prevent more than 90% of the issues related to ESD, but in order to reach the final 10%, need another protection: ionized.

And the most effective ways to generate electrostatic charge assembly equipment and surfaces is to use an ion generator (ionizer) - A device blown any charge air flow in the work area, and to accumulate on the insulating material ionization.

A common fallacy is to believe that because the workstation to bring a bowl with the insulator in the region, such as polystyrene cups or cardboard boxes, the charge will be safely dissipated. By definition, the insulator does not conduct electricity, in addition to discharge by ionization impossible.

If a charged insulator retained in the EPA, it will radiate an electrostatic field, causing the net charge onto any nearby objects, thus increasing the product ESD damage risk. While many manufacturers attempted to ban the insulating material from the EPA, but this method is difficult to implement. Insulation material is too much a part of everyday life - located comfort foam pad from the operator, the plastic cover something.

Since the use of ion generators, manufacturers can accept the fact that some of the insulating material appearing in its EPA in. Because the ion generating system continuously and can occur in any electric charge accumulation above the insulator, so for any ESD program, they are a reasonable investment.

Electronics assembly standard ion-generating device has two basic forms:

* Desktop (single fan)

* Overhead-type device (within a single unit over the top, there is a series of fan)

There are also indoor ion generator, but now mainly used for clean room environments.

Choose depends on the size of the area to be protected. Desktop ionizer will cover a single work surface and overhead ion generator will cover two or three. Another advantage is that the ion generator also prevents dust electrostatically attached to the product, may make the appearance downgrade.

However, if no ESD device testing and monitoring the effectiveness of normal, so do not have a protection plan is perfect. Class ESD control and the use of expert reports ionization failure (and therefore useless) example of ESD devices without knowing the manufacturer's failure.

To prevent this, in addition to standard ESD device, ESD vendors offer a variety of constant monitors, if a performance that is outside the specified alarm. Monitoring can be used as a standalone unit or connected together in a network. There are also automatic data collection network software, real-time display system regarding the performance of the operator and the workstation.

Monitors can be simplified ESD plans to eliminate many routine tasks, such as guaranteeing a bowl with appropriate measurement day, ionizer balance and proper maintenance, ground table is not damaged.

The first step in preventing ESD is ignored if the correct evaluation of how small details can cause irreparable damage. An effective program requires not only the use of an effective ESD protection equipment, and strict operational procedures to ensure that the behavior of all factory floor personnel are ESD safe.

While many manufacturers use automatic bowl with a tester, but can often be seen with a bowl because the operator or too loose and pass the test or fail. Many attempts by the operator with the other hand holding the tester near its simple wrist pass the test.

Nevertheless, the good news is that ESD is avoidable. Invest in the right equipment and improve safety procedures in time and money will be rewarded by a corresponding increase in yield.