The harm of static electricity to the assembly of electronic equipment- Rio Tinto brand
Date: 2013/8/3 21:24
The harm caused by static electricity to the assembly of electronic equipment Hits: 3096 Published: 2009-01-18
First, electrostatic hazards can be divided into two categories: one is the adsorption of floating dust caused by electrostatic attraction; the other is the dielectric breakdown caused by electrostatic discharge.
2. Electrostatic discharge and dielectric breakdown
The starting and discharging power source of electrostatic discharge is space charge, so its stored energy is limited, so it can only provide transient breakdown energy. Although the energy of electrostatic discharge is small, its discharge waveform is very complicated and it is more troublesome to control. Soft breakdown of semiconductor devices is related to it.
The breakdown of components caused by static electricity is the main way of electrostatic hazards in electronic equipment, and it is the most common and severe hazard in the manufacture of electronic equipment.
Electrostatic discharge can cause hard or soft breakdown of the device. Hard breakdown is a permanent failure of the device, such as the output and input of the device open or short. Soft breakdown can degrade the performance of the device and reduce its index parameters and cause hidden troubles. Because the soft breakdown can make the circuit change from time to time (caused by the decrease of the index parameters), and it is not easy to find, it causes a lot of trouble for the whole machine to run and find the fault. When the soft breakdown occurs, the equipment can still work with "illness", the performance has not changed fundamentally, it is likely to pass the factory inspection, but it may cause another failure at any time. Multiple soft breakdowns can cause hard breakdowns and make electronic equipment operate abnormally.
The human body also generates static electricity. The human body's electrostatic discharge may cause the human body to be shocked and reduce work efficiency, and may cause secondary accidents (ie, device damage), so it should be paid sufficient attention.
In military training, the human body forms static electricity because the human body converts the consumed mechanical energy into electrical energy during activities. The human body is an electrostatic conductor. When the body is insulated from the ground (for example, the sole of the shoe being worn is an insulating material), the body forms a capacitance with the ground to store the charge, and its charging voltage is generally ≤50kV. When the charge accumulates to a certain level, it will discharge to form a spark once the conditions are mature, the instantaneous discharge voltage can reach thousands of kilovolts, and the discharge power can reach several thousand kilowatts.
When the human body is charged and discharged, the human body will have different degrees of reflection. This reflection is called the shock sensitivity. When the human body is subjected to electrostatic shock, although no major physical obstacles will occur, it may affect people's work efficiency, or cause mental stress and secondary damage.
Second, the anti-static of electronic equipment that should be paid attention to
Due to the rapid development of electronic equipment, small-scale and highly integrated devices have been mass-produced, which has led to smaller and smaller wire spacings, thinner insulation films, and lower breakdown voltages. However, the electrostatic voltage generated by electronic equipment in the process of production, transportation, storage, and transfer far exceeds its breakdown voltage threshold, which may cause breakdown or failure of the device, affect the technical indicators of the equipment, and reduce its reliability. .
The prevention of static electricity is mainly to suppress the generation of static electricity, accelerate the leakage of static electricity, and perform static neutralization. When a person wears non-conductive shoes, charges can be generated and accumulated due to walking and other activities, and can reach a potential of the kilovolt level. When two different objects come into contact with each other, a charge movement occurs at the interface, and positive and negative charges are arranged oppositely to form an electric double layer. If the objects are separated, an equal amount of charge of different polarity will be generated on each of the two objects. The principle to prevent this kind of static electricity is: Exclude as much as possible the main factors that generate static electricity (object characteristics, surface state, charging history, contact area and pressure, separation speed, etc.); make the objects in contact with each other in the charged sequence Position as close as possible; make the contact area and pressure between objects small, the temperature should be low, the number of contacts should be small, the separation speed should be small, and the contact status should not change sharply. Powder, liquid, and gas can generate static electricity due to friction during transportation. Therefore, measures such as limiting the flow rate, reducing the bending of the pipeline, increasing the diameter, and avoiding vibration should be adopted.
In addition to reducing the speed, pressure, friction and contact frequency, selecting appropriate materials and shapes, and increasing the conductivity, static protection can also take the following measures: ① grounding. ② Lap (or jump). ③ Shielding. ④ Use an antistatic agent on the insulator that can hardly leak static electricity to increase the conductivity and make it easy to leak static electricity. ⑤ Use methods such as spraying and watering to increase the ambient humidity and suppress the generation of static electricity. ⑥ Use a static eliminator to neutralize static electricity. This is the most effective way to eliminate static electricity.
Third, the way to eliminate static electricity in the production process of electronic equipment
Anti-static is mainly to prevent electrostatic discharge. Controlling electrostatic discharge should start from two aspects: controlling the generation of static electricity and controlling the elimination of static electricity. Controlling the generation of static electricity is mainly controlling the process and the choice of materials during the process; controlling the elimination of static electricity is mainly to accelerate the leakage and neutralization of static electricity. These two points work together to make the electrostatic voltage not exceed the safety threshold to achieve the purpose of electrostatic protection.
Static electricity can cause harm to electrostatic sensitive devices, but it is controllable and can be eliminated.
1. Elimination of static electricity:
① Prevent the accumulation of static charge in places where static electricity may be generated. That is, take certain measures to avoid or reduce the generation of electrostatic discharge. The purpose of eliminating charge accumulation can be achieved by generating while leaking.
② Existing charge accumulation should be eliminated quickly. When an insulated object is charged, the charge cannot flow and cannot leak. You can use a static eliminator to generate anisotropic ions to neutralize the static charge. When a charged object is a conductor, a simple ground leakage method is used to completely eliminate its charge. You can install an ion fan in the work area to form a complete static safe work area, which should include at least an effective static table mat and static eliminator (Siwo Technology brand): ion fan, ion wind rod, ion air nozzle, ion Wind drum, static elimination equipment, manual electrostatic dedusting gun (ion wind gun), automatic static elimination ion wind nozzle, ion wind rod, ion copper rod, ion wind copper rod, induction static elimination rod, high voltage generator. Desktop ion fan, hanging double head ion fan, hanging three head ion fan, horizontal ion fan. Anti-static equipment desktop ion fan, induction ion air nozzle, horizontal ion fan, hanging ion fan, ion air gun, ion air nozzle, ion wind rod, induction ion air nozzle, dedicated ground wire and anti-static wrist strap Wait. If you have any questions, you can consult with the Siwo Anti-static Equipment Manufacturing Center. Manufacturing Center: Pattern Fax: 010-62716673, National Sales Hotline: 013911222754.
2. Control of static electricity: The static electricity control technology adopts comprehensive measures to control static electricity hazards within the allowable range when the accumulation of electrostatic charges is unavoidable.
① The purpose of the process control method is to generate as few electrostatic charges as possible in the production process. Preventive measures should be taken in the process of material selection, equipment installation, and operation management in the process flow to control the generation of static electricity and the accumulation of charge, suppress the electrostatic potential and discharge energy, and minimize the harm.
② The purpose of the leakage method is to eliminate static charges through leakage. Generally, electrostatic grounding is used to leak the charge to the earth, and static electricity is usually leaked by increasing the conductivity of the object.
③ The electrostatic shielding method uses a grounded shield to isolate the charged body from other objects, so that the electric field of the charged body will not affect other objects around it. This shielding method is called internal field shielding. Sometimes a grounded shield is used to surround the isolated object from the external electric field. This shielding method is called external field shielding.
④The compound neutralization method and other methods can achieve the elimination of static charge through the compound neutralization method. Usually use static eliminators (Siwo Technology brand): ion wind gun, ion fan, ion wind rod, ion wind nozzle, ion wind drum, the positive and negative ions generated to neutralize the charge of the charged body, and may make the charged object The smooth surface and cleaner surroundings reduce the possibility of tip discharge.
Static Control / Static Elimination in the Electronics Industry
With the development of nanotechnology, the integration density of integrated circuits is getting higher and higher, and the corresponding breakdown voltage (Vesd) is getting lower and lower. On the other hand, some polymer materials with high surface resistivity such as plastics , The widespread application of rubber products and the destructive nature of modern production processes, the US electronics industry's losses due to ESD in the year alone amount to tens of billions of dollars. ESD Electrostatic Discharge is a "hard virus" that is common in the electronics industry. It will occur when certain internal and external conditions are met. You can follow the following four principles to establish an effective electrostatic control program.
Embrace static control in your design
To achieve more effective ESD control, first of all, in the design of devices and products, the idea of electrostatic protection should be fully reflected, and electrostatic protection elements (ESDProtectionDevice) should be set up inside the device. Use static-sensitive devices as much as possible and The electrostatic discharge sensitive (ESDS, ESD-sensitive) device provides proper input protection, making it more reasonable to avoid ESD damage.
MOS process is the leading technology for integrated circuit manufacturing, with metal-oxide-semiconductor field effect transistors as the basic structural element. Since the gate and source of the field effect management in the MOS device is a sub-micron-level insulating slab oxide layer, its input impedance is usually greater than 1000M, and it has an input capacitance of about 5 pF, which is extremely vulnerable to electrostatic damage. Therefore, a resistor-diode protection network is set in the input stage of the MOS device. The series resistance can limit the peak current, and the diode can limit the instantaneous peak voltage. Common protective components in the device are: capacitors, bipolar transistors, thyristors (SCR, see Figure 1), etc. When ESD occurs, they respond quickly before the protected device, absorbing and releasing ESD energy, The impact of the protected device is greatly reduced. Under normal circumstances, the protection element works in its first breakdown (FirstBreakdown) area, and will not be damaged by ESD. Once the external voltage or current is overstressed, the protection element entering the SecondaryBreakdown area will be irreversibly damaged. , Lose the protective effect on the device.
At present, many manufacturers have developed devices with internal protection circuits, and a series of corresponding test standards have also been implemented. For example, the analog switch MAX4551 developed by MAXIM has 15kV ESD protection. They must be in normal operation, shutdown mode, and off. Under electrical conditions, according to standards such as IEC1340-3-1 human body model, IEC1000-4-2 air-gap discharge, IEC1000-4-4 fast transient (FTB) discharge, and other analog ESD tests, to ensure compliance with IEC1000-4 -2Level4 requirements.
In addition, the antistatic design of the production environment is also the key to ESD control. The design is based on the electrostatic breakdown voltage (Vesd) of the insulating film of the electronic device, the Vesd of the sensitive device in the whole machine, and the antistatic performance of the production equipment. Manufacturing must define and adhere to a special ESD control level, which is determined by the most sensitive components in the production process, and the production environment must guarantee this level of security. When the level of the most sensitive components is not known, the manufacturer should implement the EIA-625 standard, which defines the ESD-protected work area as a "safe area" and does not include discharge power sources that may generate more than 200V. Many international papers have proposed using the secondary collapse current as the basis for determining the electrostatic sensitivity level. A transmission line touch wave generator (TLPG) capable of accurately measuring the secondary collapse current has also become an important tool in the development of ESD protection.
Adhere to the principle of prevention, eliminate the process of generating static electricity, and minimize the processes and materials that generate static electricity during the production, storage and transportation process, which can largely eliminate the generation and accumulation of static electricity. In order to suppress the generation and accumulation of static electricity, the use of ordinary plastics, polyethylene, and styrene products with high surface resistivity, such as chemical fiber carpets, nylon clothes, and cloth instrument covers, should be avoided in the EPA area as much as possible. Once these items are rubbed, they will generate static electricity. And it is not easy to release; to reduce the dust as much as possible, the dust particles usually adhere to the charge; the operator should avoid touching the circuit board and various IC pins with hands and clothing; when cleaning the printed circuit board (PCB), use only ESD approved natural Brush and solvent; Minimize the movement of printed circuit assembly (PCA, printed circuit assembly) during all operations and inspections, and reduce the number of operations if possible; The device should be stored in a completely closed shielded container, or with the pins facing down Dissipative grounding mats; labels on PCBs or devices that track work processes (WIP, workinprocess) should also use static dissipative labels.
The logistics of sensitive devices is also a link that cannot be neglected. In this process, the components must inevitably friction with the outer packaging to generate static electricity, and the sensitive devices exposed to the external electric field (such as near high-voltage equipment) are also vulnerable to damage, and it is likely that we have not realized Under sensitive conditions, sensitive devices have been damaged, so dissipative or anti-static shielding packaging should be used for storage and transportation. Nylon and ordinary plastic products that are prone to static electricity cannot be used, and ESD devices should be removed from the package only when they are ready to be used. take out.
Safely discharge or neutralize static electricity
Similarly, no matter how strict the measures are, it is almost impossible to completely eliminate static electricity, so our third principle is to safely discharge or neutralize static electricity, of which grounding is the most basic and effective method. Grounding provides a good discharge channel for electrostatic shock, allows the electrostatic charges accumulated on the charged body to be smoothly discharged, and is quickly introduced to the ground to avoid the discharge of sensitive components. The grounding effect directly affects the entire electrostatic protection effect. If the grounding effect is poor, the entire antistatic system will fail, and the product will be in a dangerous situation full of static electricity. Only from the test discharge point to the final ground junction Any link must be kept open to ensure the safe discharge of static electricity. IEC1340-5-1 specifies the grounding resistance, and the domestic aerospace industry standard QJ1950-90 also has similar regulations. Considering it comprehensively, the grounding resistance of production and use places in the electronics industry should be below 10, and the grounding wire must be firmly connected and sufficient. Mechanical strength, otherwise sparks may be generated in loose parts. The grounding wire of the fixed equipment should be multiple pliable braided wires of 1.25mm or more. The ground wire is provided to the anti-static wrist strap, the floor and the surface of the workbench.
The static charges on insulators such as ordinary plastics cannot be eliminated by grounding, but they can be neutralized with charges of opposite polarity. At present, a static eliminator (SVCOR) is often used. Under the action of the ground current and high voltage generated by the high-voltage generator, a stable high-intensity electric field is formed, and the ionized air forms ions. It is carried out by the air flow to reach the surface of the object and achieve the purpose of neutralizing static electricity. There is a special cleaner on the ionization device, which can remove the dust on the ionization needle and maintain the normal operation of the ionization device.
Siwo Technology ion wind static elimination equipment has a dedicated ion balance circuit, which can achieve automatic ion balance. The function of eliminating static electricity can solve production problems caused by static electricity, such as solving the problem of dust collection caused by static electricity, the problem of adhesion during the processing of plastic products, and the problem of small parts jumping caused by electrostatic discharge.
A strong electric field is formed near the tip, causing the corona discharge of the air to generate positive and negative ions. The anisotropic ions move to the charged body under the action of the electric field, so that any charge accumulation that may occur on the surface of the insulator can be continuously neutralized.
Moderate control of the temperature and humidity of the environment can also effectively curb the lethality of static electricity. Both temperature and temperature have an effect on ESD. In the same atmospheric environment, the lower temperature area will have a higher relative humidity than the higher temperature area, and the increase in humidity will increase the surface conductivity of non-conductive materials and enhance the air conductivity. The static charge accumulated on the object can leak more quickly. It can be seen that the lower the ambient temperature and the higher the humidity, the more beneficial is the protection against static electricity. Therefore, when the process conditions permit, you can use air conditioning humidification, fan sprayer spray water spray, ground spraying and other methods to increase the relative humidity of the air and reduce the harm of static electricity. Of course, usually the temperature should be controlled in the range of 18-28 degrees, and the humidity should be controlled in the range of 40-65% RH.
Real-time detection of production progress and environment
The electrostatic parameters concerned in the production process are electric field strength, electrostatic potential, charge amount and resistivity. The amount of charge is the most essential physical quantity of static electricity, but it is inconvenient to measure on-site. Usually, it is used to measure the electrostatic potential on the surface of the object. The non-contact electrostatic voltmeter is often used for measurement. Very small. The antistatic performance of an object can be identified by detecting its surface resistivity or volume resistivity, and the electric field strength statically accumulates the energy accumulated in the working environment, which is very important for the determination of EPA. Commonly used testing instruments include field strength meters, hand / wrist band detectors, surface impedance testers, electrostatic voltmeters, charge meters, etc. The latest comprehensive monitoring equipment can comprehensively monitor the static state of the area, and any parameter exceeds the standard That is, automatic alarm.
Detection is a necessary means of ESD control and should be performed in real time in all links of production. Before entering the EPA, operators need to test the performance of hand / ankle straps, anti-static shoes, and anti-static work clothes; someone must be responsible for EPA testing and maintenance, and regularly check whether various ESD equipment, appliances, and grounding devices meet anti-static requirements. Management personnel should regularly check the anti-static situation of each station, and if they do not meet the requirements, they need to make corrections in real time; the test results should be archived and verified as part of the quality management system certification.
to sum up
The above four principles are the basis for establishing ESD control procedures. An effective ESD control system is far from sufficient with anti-static hardware systems. It must also have a set of training, management systems and operating procedures that are effective and implemented. American scholar Dennis Polinski believes that an effective ESD control program should include the following elements: establish an ESD protection coordinator or team, identify losses from ESD, assess your implementation process and needs, identify ESD sensitive projects, and require support from top management , Establishing and implementing procedures and regulations, personnel training and review, review, analysis, reporting, providing feedback and improvement.
ESD protection is a systematic project. It is necessary to implement the overall protection thinking and comprehensively use technologies such as voltage equalization, grounding, leakage, shielding and clamping to form a complete protection system in order to achieve obvious results.
ESD protection technology in SMT production
Editor's note: In the manufacture of electronic products, electrostatic discharge often damages the device and even causes the device to fail, causing serious losses. Therefore, electrostatic protection in SMT production is very important. This magazine invited two experts from Beijing and Shanghai respectively to write and analyze the static electricity generation sources and electrostatic protection principles in the manufacture of electronic products, and introduced some electrostatic protection technology foundations and corresponding measures in SMT production in more detail. For reference.
1. Static electricity and electrostatic hazards
Static electricity is a kind of electric energy. It is stored on the surface of an object. It is the result of the imbalance of positive and negative charges in a local range. It is formed by the conversion of electrons or ions. Electrostatic phenomenon is a general term for electrical phenomena that occur during the generation and disappearance of charges. Such as friction electrification, human body electrification and so on.
With the development of science and technology, electrostatic phenomena have been widely and effectively applied in the fields of electrostatic spraying, electrostatic textiles, electrostatic separation, electrostatic imaging and other fields. But on the other hand, the generation of static electricity will bring great harm and loss in many fields. For example, in the first Apollo manned spacecraft, three astronauts were killed due to an explosion caused by electrostatic discharge; accidents caused by explosion due to electrostatic discharge (ESD) occurred during the gunpowder manufacturing process. In the electronics industry, with the increasing integration, the inner insulation layer of integrated circuits is getting thinner and the width and pitch of interconnecting wires are getting smaller and smaller. For example, the typical thickness of the insulation layer of CMOS devices is about 0.1 μm. The corresponding breakdown voltage is 80-100V; the insulation layer of VMOS device is thinner, and the breakdown voltage is 30V. In the manufacture of electronic products and during transportation, storage and other processes, the electrostatic voltage far exceeds the breakdown voltage of the MOS device, which often causes the device to have a hard breakdown or a soft breakdown (local damage to the device), making it invalid. Or seriously affect the reliability of the product.
To control and eliminate ESD, developed countries such as the United States, Western Europe, and Japan have developed national, military, and corporate standards or regulations. There are corresponding regulations on the design, manufacture, purchase, storage, inspection, storage, assembly, commissioning, packaging of semi-finished products and finished products, and transportation of static-sensitive components. There are also stricter regulations on the manufacture, use, and management of electrostatic protection equipment. Institutional requirements. China has also formulated military and enterprise standards with reference to international standards. For example, there are standards such as the Ministry of Aerospace, the Ministry of Mechanical and Electrical, and the Ministry of Petroleum.
2. Static sensitive devices (SSD)
Devices that are sensitive to electrostatic reactions are called electrostatic sensitive devices (SSD). Electrostatic sensitive devices mainly refer to very large scale integrated circuits, especially metallized film semiconductors (MOS circuits). Table 1 is a classification table of electrostatic sensitive devices. According to the SSD classification table, different electrostatic protection measures can be taken for different SSD devices.
3． Static power in electronics manufacturing
(1) Human activities, static electricity generated by friction, contact and separation between people and clothes, shoes, socks and other objects is one of the main static power sources in the manufacture of electronic products. Human body static electricity is the main cause of the device's hard (soft) breakdown. The electrostatic voltage generated by human activities is about 0.5-2KV. In addition, the air humidity has a great influence on the electrostatic voltage. If it is in a dry environment, it will increase by an order of magnitude. Table 2 shows the relationship between relative humidity and the charging of human activities.
After the human body is charged and touches the ground wire, a discharge phenomenon will occur, and the human body will produce different degrees of electric shock response. The degree of the reaction is called electric shock sensitivity. Table 3 shows the shock sensitivities of the human body during different static voltage discharges.
(2) When the chemical fiber or cotton workwear rubs against a work surface or a chair, it can generate an electrostatic voltage of more than 6000V on the surface of the clothing and charge the human body. At this time, contact with the device will cause discharge and easily damage the device.
(3) The insulation resistance of rubber or plastic soles is as high as 1013Ω, which generates static electricity when it rubs against the ground and charges the human body.
(4) When the device encapsulated by resin, paint film, or plastic film is transported in a package, friction between the surface of the device and the packaging material can generate several hundred volts of electrostatic voltage, which can discharge sensitive devices.
(5) Various packaging, boxes, turnovers made of high-molecular materials such as PP (polypropylene), PE (polyethylene), PS (polyethylene), PVR (polyurethane), PVC and polyester, resin, etc. Boxes, PCB racks, etc. may generate 1-3.5KV electrostatic voltage due to friction and shock, which can discharge sensitive borrowings.
(6) The ordinary work surface is subject to friction to generate static electricity.
(7) The insulation resistance of insulated floors such as concrete, waxed and polished floors, and rubber boards is high, and the static charge on the human body is not easy to leak.
(8) In terms of electronic production equipment and tools: such as electric irons, wave soldering machines, reflow soldering furnaces, placement machines, debugging and testing, and other high-voltage transformers, AC / blind current circuits in the equipment will induce static electricity in the equipment. If the device's static discharge measures are not good, it will cause sensitive devices to fail during the manufacturing process. The circulation of hot air in the oven and the friction of the box, and the CO2 steam in the CO2 cryogenic box cooling box can generate a large amount of electrostatic charge.
4． ESD protection principle
It is impossible to produce static electricity in the manufacture of electronic products. The generation of static electricity is not a hazard. The hazard lies in the accumulation of static electricity and the resulting electrostatic discharge. The core of ESD protection is "meditation elimination".
ESD protection principle:
(1) Prevent the accumulation of static electricity in places where static electricity may be generated. Take measures within safety limits.
(2) Eliminate the existing static accumulation quickly and release immediately.
5． ESD protection method
(1) Use antistatic materials: metal is a conductor, and the leakage current of the conductor will damage the device. In addition, because insulating materials are prone to triboelectricity, metal and insulating materials cannot be used as antistatic materials. Instead, a so-called electrostatic conductor with a surface resistance of 1 × 105Ω · cm or less and an electrostatic subconductor with a surface resistance of 1 × 105-1 × 108Ω · cm are used as the antistatic material. For example, the commonly used static protection material is realized by mixing conductive carbon black in rubber, and the surface resistance is controlled below 1 × 106Ω? Cm.
(2) Leakage and grounding: Ground the parts where static electricity may or may have been generated, and provide static discharge channels. The method of burying the ground is used to establish the "independent" ground. Make the resistance between the ground and the ground <10Ω. (See GBJl79 or SJ / T10694-1996)
Grounding method of static protective materials: Connect static protective materials (such as table mats, floor mats, anti-static wrist straps, etc.) to the conductors leading to independent earth wires through 1MΩ resistors (see SJ / T10630-1995). The 1MΩ resistor is connected in series to ensure that the current <5mA is discharged to the ground, which is called soft ground. Equipment enclosures and electrostatic shields are usually directly grounded, called hard ground.
The grounding method of the anti-static workbench recommended in the IPC-A-610C standard is shown in Figure 1.
(3) Elimination of static electricity on the conductor: The static electricity on the conductor can be leaked to the ground by grounding. The voltage and release time of the discharge body can be expressed by the following formula:
UT = U0L1 / RC
The voltage at the UT-T moment (V) U0-the starting voltage (V) R-equivalent resistance (Ω) C-conductor equivalent capacitance (pf)
It is generally required to discharge static electricity within 1 second. That is to reduce the voltage to a safe area below 100V within 1 second. This can prevent the leakage speed from being too fast and the leakage current from causing damage to the SSD. If U0 = 500V and C = 200pf, if you want to make UT reach 100V within 1 second, then R = 1.28 × 109Ω is required. Therefore, 1MΩ current limiting resistors are usually used in electrostatic protection systems to limit the leakage current to less than 5mA. This is designed for operational safety. If the operator accidentally touches the industrial voltage of 220V in the electrostatic protection system, it will not bring danger.
(4) Elimination of static electricity on non-conductors: As for the static electricity on insulators, since the charge cannot flow on the insulators, the static electricity cannot be eliminated by grounding. The following measures can be taken:
(A) Use of ion fan-ion fan generates positive and negative ions, which can neutralize the static electricity of static power. It can be installed in the space and near the placement head of the placement machine.
(B) Use of static eliminators-Static eliminators are surfactants. The surface of the instrument and the object can be washed with static eliminating agent, which can quickly eliminate the static electricity on the surface of the object.
(C) Control of environmental humidity—increasing humidity can increase the surface conductivity of non-conducting materials and make it difficult for objects to accumulate static electricity. For example, in the northern dry environment, humidification and ventilation measures can be taken.
(D) Adopt electrostatic shielding—For equipment that is prone to static electricity, use a shielding cover (cage), and effectively ground the shielding cover (cage).
(5) Process control method: In order to minimize the generation of static electricity in the manufacture of electronic products, control the accumulation of static charges, quickly eliminate the existing static electricity accumulation, and release it immediately, from the aspects of plant design, equipment installation, operation, management system, etc. take effective action.
6. ESD protection equipment
(1) Human body anti-static system includes anti-static wrist straps, work clothes, caps, gloves, shoes, socks, etc.
(2) Anti-static floor includes anti-static terrazzo floor, anti-static rubber floor, PVC anti-static plastic floor, anti-static carpet, anti-static raised floor, etc.
(3) Anti-static operation series: including anti-static: I: as a table mat, anti-static packaging bag, anti-static logistics trolley, anti-static soldering iron and tools.
7. Static measuring instruments.
(1) Static field tester: It is used to measure the surface resistance values of table and ground. Plane structure and non-planar situations should choose different specifications of measuring instruments.
(2) Wristband tester: measure whether the wristband is effective.
(3) Human body static tester: It is used to measure the amount of static electricity carried by the human body, the impedance between the feet of the human body, the difference in static electricity between the human bodies, and whether the wristband, grounding plug, work clothes, etc. are effectively blocked. It can also be used as a primer to discharge the static electricity of the human body from the workshop.
(4) Megohmmeter: It is used to measure the impedance or resistance of all conductive, antistatic and electrostatic discharge surfaces.
8. Technical requirements for antistatic technology in electronic product manufacturing
(1) Anti-static ground electrode ground resistance <10Ω.
(2) Ground or floor mat: surface resistance value is 105-1010Ω; friction voltage is less than 100V.
(3) Wall: resistance value 5 × 104-109Ω.
(4) Work surface or pad: surface resistance value is 106-109Ω; friction voltage is less than 100V; system resistance to ground is 106-108Ω.
(5) The resistance of the work chair to the casters is 106-108Ω.
(6) Friction voltage of work clothes, caps and gloves <300V; friction voltage of soles <100V.
(7) The resistance of the wristband connection cable is 1MΩ; the system resistance is 1-1OMΩ when the wristband is worn. The resistance of the heel belt (shoe harness) system is 0.5 × 105-108Ω.
(8) The resistance of the logistics platform facing the wheel system is 106-109Ω.
(9) The surface resistance of a logistics transfer device such as a material box, a turnover box, and a PCB rack is 103-108Ω; the friction voltage is less than 100V.
(10) The friction voltage of packaging and box 1 is less than 100V.
(11) Human body comprehensive resistance 106-108Ω.
9 Anti-static measures in electronics manufacturing and general requirements for static work areas (points)
The SMT production equipment must be well grounded. The placement machine should adopt a three-phase wireless grounding method and be independently grounded. The floor, work surface pads and chairs of the production site should meet the requirements of anti-static. Keep a constant temperature and humidity in the workshop. Facilities such as anti-static material boxes, turnover boxes, PCB racks, logistics trolleys, anti-static packaging tapes, anti-static wrist straps, anti-static soldering irons and tools should be provided.
(1) Set up anti-static area according to anti-static requirements, and have obvious anti-static warning signs. According to the electrostatic sensitivity of the devices used in the work area, it is divided into 1, 2, and 3 levels, and different protective measures are formulated according to different levels.
Level 1 electrostatic sensitivity range: 0-999V
Level 2 electrostatic sensitivity range: 2000-3999V
Level 3 electrostatic sensitivity range: 4000-15999V
Above 16000V are non-static sensitive products.
(2) The room temperature of the static-safe area (point) is 23 ± 3 ° C, and the relative humidity is 45-70% RH. It is forbidden to operate SSD (static sensitive components) in less than 30% of the environment.
(3) Regularly measure the surface resistance values of the ground, table, and turnover box.
(4) Non-production items such as tableware, tea sets, bags, woolen fabrics, ⎝⎛龙博线上娱乐⎞⎠papers, rubber gloves, etc. are prohibited on the workbench in the electrostatic safety zone (point).
(5) The workers enter the anti-static area and need to discharge. Operators must wear work clothes and anti-static shoes and socks when performing operations. Before every job, you must do an electrostatic protection safety inspection before you can pass the production.
(6) Wear an anti-static wrist strap during operation, and measure whether the wrist strap is effective every day.
(7) When testing the SSD, take one piece from the packing box, tube, and tray, measure one piece, and put one piece on it. Unqualified devices after testing should be returned to the warehouse.
(8) The power-up test must follow the power-up and power-down sequence: low voltage → high voltage → signal voltage. The order of calls is reversed. At the same time, pay attention that the polarity of the power supply cannot be reversed, and the power supply voltage must not exceed the rated value.
(9) The inspector should be familiar with the model, variety, and testing knowledge of the SSD, and understand the basic knowledge of electrostatic protection.
10． Requirements for transportation, storage, and use of static sensitive components (SSD)
(1) Do not drop onto the ground during SSD transportation, and do not arbitrarily leave the packaging.
(2) Relative humidity of the warehouse where the SSD is stored: 30-40% RH.
(3) Keep the original packaging during SSD storage. If it is necessary to replace the packaging, use an antistatic container.
(4) In the warehouse, an antistatic special label should be affixed to the place where the SSD device is placed.
(5) Apply the visual inspection method when issuing SSD devices, and count the quantity in the original packaging of the SSD devices.
(6) When writing, erasing, and information protection operations on EPROM, the writer / erase device should be fully grounded, and an antistatic bracelet should be worn.
(7) Operators in assembly, welding, board repair, and commissioning must operate strictly in accordance with electrostatic protection requirements.
(8) The printed circuit boards that pass the test and inspection shall be sprayed once with an ion spray gun before packaging to eliminate the possible static charge accumulation.
11. Management and maintenance of anti-static work area
(1) Formulate anti-static management system and have someone responsible.
(2) Spare anti-static work clothes, shoes, bracelets and other personal items for use by outsiders.
(3) Regular maintenance and inspection of the effectiveness of anti-static facilities.
(4) Check the wristband once a week (or day).
(5) Check the groundability of the table mats and floor mats and the performance of the static eliminator once a month.
(6) Anti-static components rack, printed board rack, turnover box; anti-static performance of transport vehicles, table mats, floor mats is checked every six months.
Electrostatic protection of electronic products (top)
In people's daily life and work, static electricity is often encountered. So, what exactly is static electricity, its mechanism of generation and what harm does it have, and how to prevent and eliminate these harms is a problem we must consider and solve.
1. What is static electricity?
Static electricity is a kind of electrical energy. It exists on the surface of an object. It is a phenomenon that occurs when the positive and negative charges are locally imbalanced. Electrostatic phenomenon refers to a general term for the phenomenon that electric charges show in the process of generation and disappearance. For example, triboelectricity is an electrostatic phenomenon.
2. Why anti-static?
Due to the rapid development of the electronics industry, small-scale, highly integrated devices have been mass-produced, which has led to smaller and smaller wire spacings, thinner and thinner insulation films, and lower breakdown voltages. However, the electrostatic voltage generated during the production, transportation, storage and transfer of electronic products far exceeds its breakdown voltage threshold, which may cause breakdown or failure of the device, affect the technical indicators of the product, and reduce its reliability. . 由此可见，静电是电子行业发展中的一大障碍。所以预防静电必须提到议事日程上来，以确保产品的质量。
5．6．1 外出维修时应使用防静电维修箱（包） ． ．
An electrostatic connection point should be set on the product to be repaired on site, so that the maintenance technician can connect the ground wire of the wristband before opening the cover of the device. Spare parts should be transported in static shielding bags or cases unless they do not contain electrostatic discharge sensitive components. If the module is working in an exposed state, connect a static-dissipative floor mat to the product's electrostatic bonding point and use it as a work surface.
9. Related standards
In 1987, the United Kingdom made its first attempt to document practices, with the result being BS5783. Rather than calling it a standard about what tests should be performed, it is better to call it a code of practice. The second phase of this work is to translate this standard into a specification in the European organization, whose number is CECC000151, and its title is: "Basic Specification: Protection of Electrostatic Sensitive Components Part 1: General Requirements." This standard was published in 1991 and renumbered as EN1000151 in 1992. The other sections were published in 1993 (part two: requirements for low humidity conditions) and 1994 (part three: requirements for clean areas, part four: requirements for high pressure environments). The content of these sections is beyond the scope of this article.
The standard not only includes requirements for installation, maintenance, and inspection of the measures described in this article, but also details the detailed requirements of the electrostatic protection device itself, including test methods.
The continuous development of technology and processes and the experience accumulated in the implementation of standards and the widespread use of automated machinery and equipment have led to the continuous improvement of these standards, including the rationalization of their structure, and the separation of user guides from standardized versions. The revision work has been included in the international forum organized by the International Electrotechnical Commission. The new standards will be published in the IEC1340 series. There is no doubt that this is complementary to European standards. The relevant standards are shown in Table 2:
Table 2 International Electrotechnical Commission 1340 scheme structure
Guide to electrostatic principles
Definitions and terms
Static measurement method
Consumption of electrostatic charge
Resistance and Resistivity
Static Effect Simulation Method
IEC 1340-3-3 charging element model
Field effect model
Standard test methods for special occasions
Estimates of floor mats
Protection details of electrostatic sensitive components
Static control technology and method for evaluating its effect
Anti-static measures for the electronics industry
Static electricity is ubiquitous in life and production. It is from the rubbing of hands and feet to the flow of dry air. The static electricity is the last thing. If the conditions are suitable, the starting point is about a few volts and the peak is over a few hundred. Thousands of volts can be realized in an instant. These all pose a great threat to static-sensitive circuits such as CMOS, let alone the damage caused by equipment leakage. Therefore, the electronics industry takes static electricity as its enemy and makes every effort to open the door outer.
Static electricity is relative to "dynamic electricity", that is, the flowing charge in a conductor, which is a charge that does not flow under normal circumstances. It is mostly caused by friction between insulators or dry air and friction between insulators. When its energy has accumulated to a certain degree When the insulator that prevents it from being neutralized can no longer be blocked, a severe discharge occurs, that is, electrostatic discharge (ESD), and the maximum voltage at this time can reach thousands or even tens of thousands of volts. It is bound to cause damage to static-sensitive components (see Table 1 and Table 2)
Table 1.Electrostatic voltages that are easily generated at the production site.
Humidity 10 ~ 20%
Humidity 65 ~ 90%
When walking on the carpet
When walking on vinyl floors
When holding a vinyl plastic bag in your hand
When contacting polyester bags at the assembly line
When contacting the polyurethane with the operating station
Table 2 Breakdown voltage of static electricity on some electronic devices.
Minimum sensitivity for EOS / ESD
(Expressed by electrostatic voltage V)
SAW (Surface Acoustic Wave Filter)
SMD film resistor
Emitter-Coupled Logic Circuit
30 ~ 1800
100 ~ 200
100 ~ 300
100 or more
140 ~ 7000
150 ~ 500
190 ~ 2500
250 ~ 3000
300 ~ 2500
300 ~ 3000
380 ~ 7800
500 ~ 1500
680 ~ 1000
100 ~ 2500
Lightning is formed by high-voltage electrostatic discharge caused by friction between air currents and water droplets in clouds. When high-voltage charged clouds pass near buildings, some of the charges can be neutralized by the "tip discharge" effect of the lightning rod; when the amount of charge in the clouds is too large, or the clouds move When it is too fast to fully neutralize, a lightning strike will be formed by a lightning discharge from the lightning rod. In both cases, especially during the lightning strike, the entire building and the nearby ground are charged, and the damage caused by the lightning strike is mainly direct lightning and lightning induction. Because people are in the "equal-potential" state in buildings, like birds falling on high-voltage lines, they are generally not subject to lightning strikes. However, lightning induction (ultra high-voltage electrostatic induction and strong electromagnetic induction) can cause damage to electrostatic sensitive devices.
Equipment leakage, especially the small leakage that does not cause electric shock to people is not static electricity. Although most people can hardly feel it, but due to its universality (any electrical equipment always has some leakage) and high internal resistance It has the characteristics of generating peak electrical pulses with a maximum approximate power supply voltage (100 ~ 400V) and a short time, which is still enough to cause electrical overload (EOS) damage to electrostatic sensitive devices. Therefore, it is also an extremely important aspect in electrostatic protection systems.
The main mechanisms of electrostatic discharge (ESD) and electrical overload (EOS) causing damage to electronic components are: thermal secondary breakdown; metal coating melting; dielectric breakdown; gas arc discharge; surface breakdown; body breakdown and so on. See Schedule 3
Voltage-induced dielectric breakdown and subsequent high-current phenomena
Large short circuit leakage
Diode (PN.PIN Schottky)
Junction field effect tube
Bipolar integrated circuits, MOSFET and MOS integrated circuits
Secondary breakdown and micro-diffusion of microplasma caused by excess electrical energy and overheating
Increase in current beam caused by diffusion of Si and AL (electrothermal migration)
Thin film resistor
Hybrid integrated circuit (thick film, thin film) resistor monolithic integrated circuit thin film resistor
Hermetic film resistor
Dielectric breakdown, destruction of voltage-dependent current paths and micro-current paths related to Joule heat
Comb cover transistor
Burnout of metal related to Joule heat energy
Field effect structure and non-conductive cover plate
Barrier of positive ions and surface area due to ESD, causing surface inversion or grid threshold voltage drift
Performance degradation and failure
Crystal Acoustic Surface Wave
Crystal breaks due to mechanical force caused by excessive voltage
Performance degradation and failure
Small distance between electrode valves
Surface acoustic wave device
Various microcircuits in IC
Electron discharge causes electrode material to melt
Performance degradation and failure
The basic principle of antistatic should be to prevent and suppress the generation and accumulation of electrostatic charges, and to quickly and safely and effectively eliminate the generated electrostatic charges. However, many measures of antistatic are a set of system engineering, and the omissions in one link may be thousands of miles away. The embankment is broken in the anthill's urn, so don't be careless.
1. Buried anti-static ground wire:
(1). The lightning rod of the factory building is generally welded with the reinforced concrete of the building and properly grounded. When a lightning strike occurs, the grounding point and even the entire building floor will become the discharge point of high voltage and large current. "Step voltage" will be generated within the range of 20M, that is, the ideal zero potential is no longer within this range. In addition, as the neutral line of the three-phase power supply cannot be absolutely balanced, an unbalanced current will also be generated and flow into the neutral line. Grounding point, so the buried point of the anti-static ground wire should be 20 meters away from the building and equipment ground (see Figure 1)
(2). Buried method: In order to ensure reliable grounding, at least three points should be grounded, that is, a pit deeper than 1.5m every 5m, and an iron pipe or angle iron of more than 2m is driven into the pit (that is, the angle iron is inserted above 2m underground) ), Then these three places are welded together with a 3mm thick copper bar, and 16m㎡ insulated copper core wires are welded and introduced into the indoor trunk line.
(3). Appropriate amount of charcoal powder and industrial salt shall be applied in the pit to increase soil conductivity. After the landfill is measured with a ground resistance tester, the ground resistance shall be <4ω. (See Figure 2) and tested at least once a year. <>
2. Laying and testing of anti-static ground wire:
(1). All anti-static ground wires use 6m㎡ multi-strand copper-core insulated wires. Each floor or appropriate section uses copper bars or more than 40A switches, and the gate is connected to the main line to facilitate inspection and maintenance.
(2) The anti-static ground cable should be well insulated from the equipment case, workbench iron frame, work light frame, etc. to prevent short circuit, overlap or broken connection.
(3). Paving another inspection line at the "trunk end" of the segmented copper bar or switch. (1.5 ~ 2m2 is enough). Each workshop shall have 2 ~ 3 inspection points, fixed and clearly marked.
(4). Measurement: use pointer multimeter, resistance file.
a). The resistance between each antistatic test point and the antistatic ground wire is 5 ~ 15Ω, ideally it should be 0Ω. But the actual measurement is 2m㎡, the resistance from the test point to the summary point + 6m㎡, the conductor from the summary point to the measured point The sum of the point resistances, this value is about 5-15Ω and is basically unchanged.If the measurement result tends to infinity, it is because the anti-static ground line or the measurement line has a broken wire, and it should be repaired in time.
b) The resistance between the anti-static ground and the equipment ground. This resistance value is composed of the line resistance of the anti-static ground wire itself + the line resistance of the equipment ground wire + the ground resistance between the two ground wires. However, due to the dryness and wetness of the ground between the two ground wires The influence of ground current is very complicated, especially the current, the frequency of the direction, etc. are changing every moment, and the measurement result is mainly determined, so it can only be measured with a pointer meter, and its value ranges from a dozen ohms to hundreds of K It is normal, only that there is no short circuit or open circuit between the two places.
3. Anti-static floor (see Figure 4):
The most standardized anti-static floor is a composite structure similar to anti-static rubber.The lower layer is a conductive layer connected to the anti-static ground, and the upper layer is an insulating anti-static generation layer, which will not generate static electricity due to walking friction. The conductive layer should be insulated when laying. The mat is separated from the building floor and wall to prevent the floor from static electricity during a lightning strike, and the conductive layer is connected to the anti-static ground through a 1MΩ20W resistor. It plays a role of electrostatic shielding and electromagnetic shielding. This floor is too expensive, but it can be effective Prevent various hazards of lightning and static electricity.
General electronic factories often use simple anti-static floors (only the insulation anti-static generation layer is mostly paint or floor glue), which is directly laid on the building floor, which greatly reduces the cost and can also prevent the static electricity generated by walking. The ultra-high voltage electrostatic induction and strong electromagnetic induction generated by lightning strikes have poor protection.
4.Anti-static work surface: as shown in Figure 4
The green surface of the anti-static rubber is an anti-static generation layer, which has a large resistance and a surface resistance of 108 ~ 1010Ω.
The black surface of the antistatic rubber has a small resistance, the surface resistance is 104 ~ 106, and it is well connected to the green surface, which can ensure a good ground. It can act as an electrostatic shield and discharge. It can be connected by a buckle, and a dedicated electrostatic bracelet wire (included) 1M resistor) ground. Or put a 0.2mm thick iron plate or copper foil on the insulating table, solder the wires to the electrostatic ground wire through the 1MΩ resistor, and then flatten the antistatic rubber (black side down, close to the conductive sheet). The 1MΩ resistor also provides a static discharge path to prevent over-speed discharge from sparking and isolating.
Even chairs (stools) should be paid attention to. Most production lines use ordinary plastic stools, which are prone to generate static electricity through friction with clothing. If possible, use anti-static chairs and connect them to static ground through 1MΩ resistors. Put on a static cloth.
5.Grounding and testing of electric equipment such as electric irons, small tin furnaces, test instruments:
Electric soldering irons, small tin furnace testing instruments, etc. must be properly connected to the equipment ground with a three-terminal plug. It is not difficult to do so, but because of frequent occurrences such as: the socket ground terminal is loose, the wire is disconnected, and the soldering iron tip is oxidized and connected to the casing (Ground) disconnection and other phenomena, so it should be tested every shift, and can be tested with self-made simple on-off indicator lights, and immediately replace the problem if found.
6. Anti-static clothing (clothing, shoes, gloves, etc.):
The so-called anti-static clothing is woven with special synthetic fibers. Generally, rubbing and friction will not generate static electricity. However, it is not a static shielding clothing. It cannot eliminate the static electricity generated by other clothing on the body. Therefore, it should be worn only inside. A shirt or underwear, wearing an anti-static clothing. Wearing multiple pieces of chemical fiber in winter, and wearing anti-static clothing with wool clothing is not very useful. Therefore, it is more important to control the temperature and humidity of the environment, and wearing an electrostatic bracelet is more important than electrostatic clothing. Anti-static gloves are used to prevent the generation of static electricity; to isolate hands from products (insulation); to prevent sweat from contaminating the product, and so on, are necessary.
The anti-static wristband is grounded by a stainless steel case that is close to the wrist, and is grounded by a wire and an iron clip through a 1MΩ resistor in the wire. The purpose is not only to discharge the static electricity on the human body at any time, but also to prevent sparks caused by rapid discharge. Causes damage and acts as an isolation. And broken wires or poor contact can make the static hand ring virtual. The so-called wireless bracelet can't actually discharge the static charge carried by the human body.
(1). Standardize the wearing and clamping method of electrostatic bracelet:
a. The stainless steel case of the electrostatic wristband should be worn on the inside of the left wrist, where the contact resistance is the smallest.
b. It should be in close contact with the skin, not loose, and not separated by clothes.
c. Alligator clips should be used to hold the exposed part of the electrostatic ground wire at the root instead of using the front teeth.
d. When leaving work or walking, the operator can take off the bracelet, mobile staff (cadres, quality control) should remove the clip and wrap it around the wrist for mobile use.
(2). The static electricity ring should be tested and recorded in the morning and afternoon each shift. The tightness is subject to passing the test. Any unqualified should be adjusted or replaced immediately.
(3). Do not wear wireless bracelet.
8.Install ion fan:
The temperature of the pre-heating part of the wave furnace is 80 ~ 120 ℃, and static electricity is easily generated under such high temperature and dry hot air. The ion fan uses high pressure to ionize the air into positive and negative ions, and the fan blows the air containing a large number of positive and negative ions into the furnace. In order to neutralize the static electricity generated by the hot air on the PCB and components, an ion fan should be installed at the entrance of the wave furnace. At the entrance of the anti-static work area, the starting point of the conveyor belt or above can also be installed with an ion fan according to actual needs.
9.Add anti-static cleaning roller to the conveyor belt:
Self-made simple device: Wrap a hard plastic tube with a length slightly smaller than the width of the conveyor belt around a towel cloth (it should be flat), and then use iron rods (as shafts) to fix it at both ends of the conveyor belt after wetting. The bottle method is constantly humidified. When the conveyor belt is started, the roller rotates with the conveyor belt under its own weight to clean, humidify and prevent static electricity. This simple self-made device can function as an ion fan of the conveyor belt in certain occasions.
10. PCB on the assembly line (mainly refers to post-DIP repair welding, testing, assembly and other processes) should be equipped with an anti-static sponge pad to prevent static electricity and board surface scratches. Transfer between processes using anti-static board storage trucks Or the card box (the surface resistance is below 106Ω), and the ground is properly connected through a 1MΩ resistor.
It is important to distinguish between static shielding materials (bags) and antistatic materials (bags). Antistatic materials (bags and pads) are mostly pink. They are only used as cheap pads and intermediary packaging for electrostatic sensitive devices. Only static electricity is generated, and if there is an electrostatic discharge, it can pass through these anti-static materials to cause harm. Static shielding packaging is mostly silver, black, gray, aluminum foil-shaped opaque and black, gray translucent materials, and now has a grid-like shape. Full transparent materials, etc., the basic principle is to vacuum-coat a layer of aluminum on the outside of the antistatic material as a conductive electrostatic shielding layer. When an electrostatic potential is generated, the shielding layer will evenly distribute the induced electrostatic potential across the entire packaging surface, reducing the surface potential difference. Prevents local high-potential electrostatic discharge, and also has a good shielding effect on high-frequency and strong electromagnetic fields. With different protection levels, the conductive layer of the electrostatic shielding packaging material is also divided into: outer resistance layer-insulation film-aluminum foil layer-insulation film; insulation film ─Aluminum foil layer─Insulation film; Vacuum coating layer─Insulation film; Printed conductive grid layer─Insulation film and other grades. A little attention can be found when the IC leaves the factory. The outer packaging is 2 ~ 3 layers of electrostatic shielding material, and the internal supporting materials (such as push plates and feeding tapes) are black high-resistance conductive materials, about 106MΩ, which only serves to shield and neutralize the electrostatic potential of each pin. The role of static discharge path. When static-sensitive components (such as ICs) and products are shipped, they must be packaged with static shielding materials instead of anti-static bags.
11. Regulation of temperature and relative humidity:
Electronic operations, especially SMT, have high requirements on temperature and humidity.The general temperature is controlled at 18-28 ° C. Too high or too low will affect the normal operation and accuracy of the equipment; the relative humidity should be 50% to 85%, If it is too low, it is easy to generate static electricity (see Table 1). If it is too high, the equipment is prone to dew condensation and the solder paste contains more water, so monitoring and regulation should be strengthened. For antistatic, when the relative humidity in autumn and winter is low, you can use a humidifier or wet cloth Local solution.
(1) The electric soldering iron should be an antistatic low voltage constant temperature soldering iron as far as possible and well grounded.
(2) Low-voltage DC electric screwdriver (electric driver) using a ground wire.
(3) Anti-static brushes should be used for small batch cleaning of PCBs. Do not use ordinary plastic brushes.
(4) In some occasions, ceilings and walls should use antistatic materials. Generally speaking, even ordinary gypsum boards and lime-painted walls can be used, but the use of plastic ceilings and ordinary wallpapers and plastic wallpapers is prohibited.
If conditions are available, consider adding a "hand-held non-contact static tester", so that you can monitor the generation, size, and tracking of the defects caused by static electricity in real time to understand the improvement effect. Because its price is too expensive, most companies dare not ask.
14.Monitoring and recording:
The anti-static measures must be implemented by a special person and a system can be implemented. Otherwise, all hardware investment may not be effective.
(1). Personnel: Two people should manage, test, and record part-time. In most cases, two people are required to cooperate and prevent the flow of personnel.
(2) Tests and records: In summary, the following tests and records should be completed every day.
a. Static test point -------- Electrostatic ground Analog multimeter
Electrostatic ground ----------- Equipment ground Resistance measurement
b. Grounding the tip of the soldering iron / temperature measurement of the soldering iron tip.
c. Tin furnace grounding / tin furnace temperature measurement.
d. Test instrument ground measurement.
e. Electrostatic wristband grounding test. Electrostatic wristband tester
f. Indoor temperature / relative humidity measurement and regulation. Temperature / hygrometer.
(3) Check the implementation of the staff's dress and anti-static regulations in the anti-static work area.
(4). If necessary, use a static tester to measure the static voltage in various situations at the work site and on the assembly line.
The electrostatic voltage should generally be less than 100V, and in special cases should be less than 25V.
15.Training and literacy: Anti-static knowledge / measures should be taken as an important content of all staff training so that every employee can understand and form good professional habits. For example:
Clothing, drawings and other materials must not touch components, drawings and materials should be placed in anti-static document bags and hung;
Plastic boxes, such as leather, cardboard, glass, etc., which are prone to static electricity, are not allowed to be stacked on static safety workbenches;
You must load the electrostatic ring and gloves before you can touch the components. Hold the PCB or sensitive devices by the edges as much as possible to avoid touching their leads and terminals;
Consciously abide by and implement anti-static rules and regulations.