How to protect against static electricity in electronic equipment
Electrostatic discharge (ESD) is a familiar and underestimated source of circuit board and component damage in electronic assembly. It affects every manufacturer, regardless of its size. 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. ESD occurs very quickly with extremely high intensity, and usually generates enough heat to melt the internal circuits of the semiconductor chip, and looks like small bullets/bullet holes blown out under the electron microscope, causing immediate and irreversible damage.
What's more serious is that only one-tenth of this hazard is so bad that the entire component tested in the final test fails. In the other 90% of cases, ESD damage causes only partial degradation-meaning that the damaged component can pass the final test unnoticeably, and only has premature field failure after shipment to the customer. The result is the worst reputation and the most costly place for a manufacturer to correct any manufacturing defect.
The main product used to prevent ESD is a wristband, with curled corduroy and a dissipative surface or anti-static rubber mat-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, the 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 electrical charge accumulated on the insulating material.
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:
1. Desktop type (single fan; 2. Over-the-top type equipment (in a single over-the-top 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 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 statically adhering to the product, which may degrade the appearance.
However, if there is no normal testing and monitoring of the effectiveness of ESD equipment, no protection plan is perfect. Leading 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, 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 a standalone 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 workbench ground point is not damaged.
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 factory floor personnel is ESD safe.
Although many manufacturers use automatic bowl strap testers, it is often seen that operators pass the test or fail because the bowl strap is too loose. Many operators attempt to pass the test by simply holding the tester with the other hand* near their wrist.
Nonetheless, the good news is that ESD is avoidable. The time and money invested in the right equipment and improving safety procedures will be rewarded with a corresponding increase in the pass rate.