ESD protection equipment
To control or monitor static electricity, various types of equipment may be used.
One, personnel grounding strap
Personnel handling ESD products should wear a wrist, leg or ankle grounding strap that is in contact with the skin. The function of these grounding straps is to discharge the static charge of the human body to the ground. In the case of not using a personnel grounding wrist strap, a human body grounding system consisting of conductive shoes or heel grounders and an ESD protective floor can be used.
1. Issues to be considered for personnel grounding straps
The personnel grounding strap should have an appropriate resistance to ground to prevent personal safety from being endangered, and the resistance to ground should be able to limit the current to less than 5mA. Examples of personnel grounding straps include:
A. Carbon-impregnated volume conductive plastic grounding strap
B. Volume conductive plastic grounding strap
C, retractable metal grounding strap
D. Extensible metal zone with insulated external surface
E. Elastic cloth braided grounding straps connected to wires or conductive fibers.
Each of the above-mentioned various grounding straps may have protective resistance, or be connected to the grounding strap itself, or connected to the grounding wire. For human safety, the resistor should be placed close to the contact point with the human skin to reduce the chance of short-circuit and shunting of the quilt to the ground. The metalized outer surface or the carbon-impregnated grounding strap should have an insulated outer surface to prevent unintentional hard work.
The personnel grounding strap shall be directly connected to the ground through a protective resistor. The personnel grounding strap should include a quick strap release mechanism so that the straps can be released in an emergency.
The personnel grounding strap should be evaluated in detail from two aspects: personal safety and charged materials or other pollutants caused by the components of the grounding strap. Carbon-impregnated materials and metal wires can shed conductive materials, just as the metal covered on synthetic fiber fabrics is used on some types of grounding straps.
Second, the protective floor
The protective floor material can conduct (static) electricity or dissipate static electricity. Carpets, vinyl boards, vinyl floor tiles and terrazzo, etc. To use conductive (static) electric synthetic resin flooring, conductive adhesives should be used. Since the waxed surface is highly resistive and easy to generate static electricity, hard surface floors should not be waxed. Conductive (static) electric shoes, insoles, or heel grounders should be used to discharge the body charge on the conductive (static) floor. These items can only be worn inside the ESD protection area and should be kept clear so that pollutants do not prevent their communication interface with the floor. People sitting on the workbench in the ESD protection work area often lift their feet from the floor. Pushing toward the work chair, which helps the floor to eliminate the charge. Therefore, a grounded conductive work chair is often required in the case of a protective floor.
The protective floor should have enough resistance to the ground to limit the current below 5mA.
Painted or enclosed concrete floors and painted wooden floors are typical main sources of static electricity, and should be covered with ESD protective floors or floor mats or treated to provide ESD protection. The floor should be tested regularly, using an electrostatic field meter to measure the amount of charge generated when a person walks over the floor.
Due to electrical safety requirements, protective floors cannot be used in certain areas. In some military installations and operating platforms, insulating floor mats are required for electrical safety, which is a practical application. In these cases, the personnel grounding strap should provide ESD protection to the required degree.
Three, ESD protection floor mat
ESD protective floor mats can be made of materials with various conduction (static) electricity or dissipation resistivity ranges. These floor mats are intended for temporary or semi-permanent installation on existing floors. Floor mats are only effective as part of a continuous human body grounding system consisting of floor mats and conductive (static) shoes or heel grounders.
Fourth, the work surface
Workbenches that come into contact with ESDS products and personnel should have an ESD-protected work surface. The surface of the workbench should be connected to the ground through a grounding cable. The resistance of the grounding cable on the top of the workbench should be placed in the point or accessory that is in contact with the top surface of the workbench. At the same time, it should have a large enough resistance to ground to limit the current below 5mA. Here, all parallel resistance to ground should be considered, for example Ground the wrist strap, desktop, and conductive (static) or dissipative static electricity. And the quilt can be installed on the workbench temporarily or permanently. The materials available for the work surface are listed as follows:
A. Carbon impregnated plastic
B. Plastics treated with surfactants
C. Laminate
D Other materials that are processed or made in a certain way to conduct (static) electricity or dissipate static electricity
Five, static detector
Types of static detectors include electrometer amplifiers, electrostatic voltmeters, electrostatic field meters, and foil deflection electroscopes. The electrostatic field reading of the electrostatic field measuring instrument is obtained by a non-contact probe or sensor through the induction of a charged object, and the primary reading is provided by the charged object at a calibrated distance and is given by the strength of the electrostatic field or the static voltage. Some electrostatic field measuring instruments use radioactive sources similar to those of radioactive ion generators. Under certain circumstances, radioactive meters will cause beta fog on the radiation detection film, which may lead to false radiation exposure indications. They are not suitable for use in the size of the static charge that exists in the power of the atom. In addition, they can be used to measure the approximate amount of static charge and triboelectric charge generated by human movement.
Sixth, the selection of electrostatic detectors need to be considered
The main defect of the simple analog electrostatic meter is its response time. Most meters cannot respond to signals with fast rise times and short pulses. High-speed storage oscilloscopes can be used to measure static charges generated and dissipated in a shorter time than the response time of the meter. When measuring instantaneous ESD voltage, analog meters may be better than digital meters due to their faster response time.
To monitor and identify the ESD protection work area, a portable electrostatic meter can be used. In places where Class 1 sensitive products are handled, more sophisticated laboratory-type detectors may be required.
When choosing a table turtle detector, the characteristics to consider are:
A. Sensitivity at small voltage levels that can be accurately measured
B. Response time
C. The voltage range that can be measured
D, accuracy
E. Radioactive drive or electric drive
F. Portability
G. Durability
H. Operation and simplicity and legibility
I. Accessories such as mobile probe and strip recorder output
J. Calibration requirements
K, maintainability
Seven, electrostatic sensor and alarm
The electrostatic sensor and alarm system is suitable for continuously monitoring the electrostatic level generated in a protection zone. Some systems have multiple remote sensors that can monitor several stations at the same time. Some systems also include a strip pattern recorder that provides a permanent record of static electricity in a certain area.
8. Other equipment
Now, there are a variety of auxiliary equipment that can help users establish a protective zone and monitor the equipment in the protective zone. This equipment consists of a small static voltage detector that presets audiometric and audible alarms at a predetermined voltage level, a surface resistivity detector that uses light emitting diodes to read out and displays the resistivity range, and a continuous wristband monitoring device. . The selection and use of these devices should be based on a complete knowledge of their functions. In addition, it is highly desirable to calibrate any detectors, monitors, alarms, or other instruments used in the implementation or supervision of ESD control programs. The ability to repair and calibrate each product on-site should be considered part of the selection process.
Nine, electrical equipment, tools, soldering irons, soldering baths, flow soldering equipment
The soldering iron, solder bath and or flow soldering equipment should be properly grounded. The resistance from the hot end of a soldering iron to the ground should be less than 2Ω. The potential difference between the ground and the hot end of the soldering iron should not be greater than 2MV (effective value). Other electrical power supply equipment that comes into contact with ESDS products should also be properly grounded. The ESD protection welding inhaler should be grounded.
10. Assembly, testing and packaging equipment
During the design and implementation of the ESD control program, the ESD damage potential caused by assembly, testing, and packaging equipment is often ignored. For example, vacuum pick-up and tin solder** tools can be caused by airflow during electronic assembly operations. The source of triboelectric charge. Automatic and semi-automatic parts handling machines commonly used for picking up, positioning, and soldering surface mount devices can also be ESD voltage sources that can cause damage. Other possible damage to the ESD voltage sources include automated stations that use parts automatic feeding troughs, integrated electric rails and continuous shaking parts containers, and robot assembly arms and fixtures when the assembly board increases. Automated testers, such as "bed-of-needle" detectors, are also possible sources of static voltage during operation.
Automatic packaging equipment, including foaming and shrinking packaging devices and foam plastic installation in place equipment are other possible damage to the static voltage source.
Due to the wide variety of available semi-automatic, automatic, and robotic assembly, testing and packaging equipment, no general conclusion can be drawn about the suitability or non-applicability of any specialized machine or equipment. In order to obtain qualification data on ESD, it is extremely difficult to include damage during operation of this model. For this reason, each user should rely on the sensitivity level of the product and the specific semi-automatic, automatic and robotic equipment selected to evaluate the effect.