Static electricity prevention technology
In order to effectively fight and prevent electrostatic discharge (ESD, electrostatic discharge), the right equipment must be used in the right way. Thanks to a series of powerful closed-loop ESD prevention, monitoring and ionization equipment, ESD can now be regarded as a process control problem.
Electrostatic discharge (ESD) is a familiar and underestimated source of circuit board and component damage in electronic assembly. It affects every manufacturer, no matter how big or small it is. Although many people think that they are producing products in an ESD safe environment, in fact, ESD-related damage continues to cost the world's electronics manufacturing industry billions of dollars a year.
What exactly is ESD? Electrostatic discharge (ESD) is defined as the discharge (current of electrons) to or from a charge (insufficient or surplus of electrons) that has been electrostatically (fixed). The charge is stable under two conditions:
When it "sinks" into a conductive but electrically insulating object, such as a metal screwdriver with a plastic handle.
When it resides on an insulating surface (such as plastic) and cannot flow on it.
However, if an electrically insulated conductor (screwdriver) with a sufficiently high electric charge is close to an integrated circuit (IC) with an opposite electric potential, the electric charge "crosses", causing electrostatic discharge (ESD).
ESD occurs very quickly with extremely high intensity, and usually generates enough heat to melt the internal circuit of the semiconductor chip, and looks like a small bullet hole blown out under the electron microscope, causing immediate and irreversible damage.
What’s more serious is that this hazard is only one-tenth of the time so bad that it causes the entire component tested after * to fail. In the other 90% of cases, ESD damage causes only partial degradation-meaning that the damaged component can pass the *post-test unnoticeably, and only has premature field failure after it is shipped to the customer. The result is * reputational damage, a place for a manufacturer to correct any manufacturing defects * to pay a price.
However, the main difficulty in controlling ESD is that it is invisible, but it can damage electronic components. To produce an audible "tick" discharge requires a relatively large charge of about 2000 volts to accumulate, while a small electric shock can be felt at 3000 volts, and a spark can be seen at 5000 volts.
For example, common components such as complementary metal oxide semiconductor (CMOS, complementary metal oxide semiconductor) or electrical programmable read-only memory (EPROM, electricall programmable read-only memory) can be affected by ESD potential differences of only 250 volts and 100 volts, respectively. Destruction, and more and more sensitive modern components, including Pentium processors, can be destroyed as long as 5 volts.
The problem is compounded by daily activities that cause damage. For example, walking across a vinyl factory floor creates friction between the floor surface and the shoes. The result is a purely charged object, accumulating a charge of 3 to 2000 volts, depending on the relative humidity of the local air.
Even the friction caused by the natural movement of workers on the stage can generate 400~6000 volts. If the worker has handled the insulator during the process of unpacking or packing the PCB in the foam box or bubble bag, the net charge accumulated on the surface of the worker's body can reach approximately 26,000 volts.
Therefore, as the main source of ESD hazards, all workers entering the electrostatic protected area (EPA, electrostatic protected area) must be grounded to prevent any accumulation of charges, and all surfaces should be grounded to maintain everything at the same potential to prevent ESD occurs.
The main product used to prevent ESD is a wristband, which has curled corduroy and a dissipative surface or bedding-both must be properly grounded. Additional aids such as dissipative footwear or heel straps and suitable clothing are designed to prevent personnel from accumulating and maintaining a net charge when moving in an electrostatic protected area (EPA).
During and after assembly, PCB should also prevent ESD from internal and external transportation. There are many circuit board packaging products that can be used in this area, including shielding bags, shipping boxes, and movable carts. Although the correct use of the above equipment will prevent 90% of ESD-related problems, in order to reach the last 10%, another kind of protection is needed: ionization.
The most effective way to neutralize assembly equipment and surfaces that can generate electrostatic charges is to use an ionizer-a device that blows out a stream of ionized air over the work area to neutralize any charge accumulated on the insulating material.
A common fallacy is that because the bowl belt is worn at the workstation, the insulators in the area, such as polystyrene cups or cardboard boxes, will be safely dissipated. By definition, an insulator does not conduct electricity, except that it is impossible to discharge through ionization.
If a charged insulator remains in the EPA, it will radiate an electrostatic field, causing a net charge to any nearby objects, thus increasing the risk of ESD damage to the product. Although many manufacturers attempt to ban insulating materials from their EPA, this method is difficult to implement. Insulation is too much part of everyday life-from the foam cushion that the operator sits on comfortably, to something in the plastic cover.
Due to the use of ionizers, manufacturers can accept the fact that some insulating materials appear in their EPA. Because the ion generation system continuously neutralizes any charge accumulation that may occur on the insulator, they are a reasonable investment for any ESD program.
There are two basic forms of ion-generating equipment in standard electronic assemblies:
Desktop type (single fan)
Overhead type equipment (in a single overhead unit, there are a series of fans)
There are also indoor ion generators, but they are mainly used to clean the room environment.
The choice of depends on the size of the area to be protected. The desktop ionizer will cover a single working surface, while the overhead ionizer will cover two or three. Another advantage is that the ionizer can also prevent dust from attaching to the product statically, which may degrade the appearance.
However, if there is no normal testing and monitoring of the effectiveness of ESD equipment, then no protection plan is perfect. Top ESD control and ionization experts reported examples of manufacturers who used failed (and therefore useless) ESD equipment without knowing the failure.
In order to prevent this situation, in addition to standard ESD equipment, ESD suppliers also provide various constant monitors, which automatically alarm if a performance exceeds the regulations. The monitor can be used as an independent unit or connected together in a network. There is also network software for automatic data collection, which displays the system performance of related operators and workstations in real time.
The monitor can simplify ESD planning by eliminating many daily tasks, such as ensuring that the bowl belt is properly measured every day, the ionizer is balanced and properly maintained, and the grounding point of the workbench is not damaged.
in conclusion
The first step to prevent ESD is to correctly evaluate how small details may cause irreparable damage if ignored. An effective plan requires not only the use of effective ESD protection equipment, but also strict operating procedures to ensure that the behavior of all plant personnel on the ground is ESD safe.
Although many manufacturers use automatic bowl belt testers, it is often seen that operators pass the test or fail because the bowl belt is too loose. Many operators attempt to pass the test by simply holding the tester close to their wrist with the other hand.
Nevertheless, the good news is that ESD is avoidable. The time and cost invested in the right equipment and improving safety procedures will be rewarded with a corresponding increase in the pass rate.