ESD protective equipment, equipment and their use
To prevent static hazards, people have developed a variety of ESD protection products and equipment, also known as anti-static supplies, equipment, used in electronic production environments. Due to the wide variety and performance of ESD protection products. To achieve better results, the performance is described in detail below:
1. Human body ESD protection products
There are roughly six types of ESD protection products for human body use.
(1) ESD protective overalls (also known as anti-static overalls)
The ESD protective suit is made of conductive fiber. When rubbed against other objects, the generated static electricity leaks through the contact of the conductive fiber with the human body or through the corona discharge and diffusion between the conductive fibers. Thereby antistatic accumulation.
There are three types of materials and conductive fibers used in ESD protective clothing:
A. Metal fiber clothing: clothing made of a blend of 8 to 50 micrometers of stainless steel wire and cotton.
B. Carburizing (or metal) clothing: spraying and plating conductive materials (conductive carbon black, metal powder) on the surface of synthetic fibers.
C. Conductive synthetic fiber clothing: a conductive material is mixed into the synthetic fiber.
There are the following requirements for the design and use of ESD protective clothing:
Non-antistatic fabrics are generally not used as a lining. When used, the lining used must not exceed 20% of the total lining area.
No metal accessories may be used for the entire garment. When it must be used, it should not be exposed directly to the surface of the garment, and the metal should be discharged.
The detection charge of each piece of ESD protective clothing should be lower than 0.6 microcoulomb/piece of the national GB12014-89 "anti-static work". For the class I ESD protection area, the ESD protective clothing used should be tested according to the method specified in GB12014-89. The power should not exceed 0.01 micro coulombs/piece, the level II area should not exceed 0.1 micro coulombs/piece, and the level III area should be 0.4 micro coulombs/piece.
When wearing ESD protective clothing, it must be used with ESD protective shoes (anti-static shoes).
Re-examination of ESD protective clothing is transmitted every other year according to national standards, when the charge exceeds the above specified value, it shall not continue to be used.
Pure cotton clothing cannot prevent static electricity from accumulating in an environment with a relative humidity of less than 40%, so it is not suitable for ESD protective clothing.
(2) ESD protective shoes (anti-static shoes)
The sole of the shoe is made of synthetic rubber with conductive carbon black, which is used to leak static electricity from the ESDS device operator and prevent static accumulation of the human body.
The national standard GB4386-84 "anti-static rubber sole shoes, conductive rubber sole shoes safety technical conditions" specified anti-static sole resistance value of 5 × 104 ~ 108 ohms, conductive shoe resistance is not greater than 1.5 × 105 ohms. The difference between the anti-static shoes and the conductive shoes is that the anti-static shoes can be used in an environment with electrical equipment to prevent electric shock of 250 volts to the human body. Conductive shoes cannot be used in environments where there is a risk of electric shock.
To ensure the elimination of static electricity in the human body, the resistance between the ground and the earth when wearing the above shoes should be no more than 108 ohms and 0.5 x 105 ohms, respectively. During the transfer process, the bottom of the shoe must not be contaminated with any insulation, and the use of insulating socks is prohibited.
(3) Anti-static wrist straps and foot straps
Anyone who operates ESDS devices should use an anti-static wrist strap and foot strap. The function of the wrist strap and the foot strap is to quickly leak static electricity to the ground.
A general anti-static wrist strap consists of a buckle, a strap, and a grounding cable. The strap, buckle and grounding cable have good electrical contact. To ensure the safety of the operator, a 1 megaohm resistor is usually placed on the grounding connection of the wristband to limit the current flowing through the human body when the electric shock is not more than 5 mA.
There are two types of wrists: one for the general ESDS device operating environment, and its resistance to ground series is 1 megohm. The other is used for special environment ESDS device operation, the resistance of the series connection to the ground is about 50 ohms (see ETS).
When using the wristband, make sure that the wrist strap is in good contact with the wrist, grounding cable, and grounding wire.