ESD protection and elimination methods in switching power supply design and production

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ESD protection and elimination methods in switching power supply design and production [Copy link]

1 Introduction

ESD protection is a very important part in the design or production of switching power supplies.

The degree of damage caused by static electricity varies according to the type of electronic components. Even the lowest static voltage of 100V can cause damage to them. In recent years, as electronic components have become more integrated, the corresponding static voltage has also been required to be continuously reduced.

The static voltage induced by the human body is usually above 2-4KV, which is usually caused by slight movements of the human body or friction with insulating materials. In other words, if the static potential in our daily life comes into contact with IC, almost all ICs will be destroyed. This danger exists in any working environment where no static protection measures are taken. The damage of static electricity to IC is not only reflected in the manufacturing process of electronic components, but also in the process of IC assembly and remote transmission.

When designing a switching power supply, you can actually take some static protection measures, such as adding a 104 capacitor to the VCC pin of the IC and a 100K resistor between the G pole of the MOS and the ground.

What is more important is the control of the process during the production. Below, we will have a deeper understanding of static electricity and its protection. The sources of static electricity include the human body, plastic products, related testing instruments and equipment, and the electronic components themselves.

2 Static Source

1. Human body static electricity:

The human body is the most important source of static electricity. There are three main reasons for this. First, the human body has a wide contact surface and a large range of activities. It is easy for the human body to be charged by contact or friction with objects with static charges. There are also many opportunities to transfer the charge carried by the human body to components or discharge through devices. Second, the capacitance between the human body and the earth is low, about 50~250PF, with a typical value of 150PF, so a small amount of human static charge can lead to very high static electricity. Third, the human body has a low resistance, which is equivalent to a good conductor. Therefore, the human body is easily induced to be charged in an electrostatic field, and charging of one part of the human body can cause the whole body to be charged.

2. Static electricity of measuring instruments and equipment:

Instruments and equipment can also carry static electricity due to friction or electrostatic induction. For example, during the transmission process, the transmission belt generates static electricity due to contact and separation with the shaft, or the metal shell of the instrument with poor grounding generates static electricity in the electric field. After the instrument and equipment are charged, contact with components will also generate static discharge, causing static damage.

3. Static electricity of the device itself:

The friction between the shell of electronic components (mainly ceramic, glass and plastic packaging tube shell) and insulating materials will also generate static electricity. After the device shell generates static electricity, it will be released through a grounded pin or external lead, which will also cause static electricity damage to the device.

4. Other sources of static electricity:

In the process of manufacturing, installing, transporting, testing, and storing electronic devices, various items made of insulating materials are encountered, such as workbenches, work clothes, packaging containers, etc. These items will generate high static electricity when they rub against each other or the human body.

3 Switching power supply production process

In the production process of switching power supplies, electronic components may be damaged by static electricity. The production process can be divided into:

1. Power printed circuit board (semi-finished product) production process:

Components receiving, acceptance, storage, PCB insertion, welding, quality control, semi-finished product warehousing;

2. Power supply assembly process:

Circuit board (semi-finished product) receiving, assembly, aging and burn-in, electrical parameter testing, quality control and shipment.

In the whole process, at every small step in every stage, the components may be affected by static electricity. In fact, the most important and easily overlooked point is the process of conveying and transporting components. In this process, not only is static electricity easily generated due to the movement of the package, but the entire package is easily exposed to high-intensity electromagnetic fields from the outside world (such as passing near high-voltage equipment, frequent movement of workers, rapid movement of carts, etc.) and damaged, so special attention should be paid to the conveying and transportation process to reduce losses.

4 General methods for electrostatic protection of switching power supplies

The fundamental purpose of electrostatic protection is to prevent the hazards caused or potentially caused by the mechanical and discharge effects of static electricity through various protective measures during the manufacturing and use of electronic components, semi-finished assemblies, and power supplies, or to limit these hazards to a minimum, so as to ensure that the design performance and performance of components, semi-finished assemblies, and power supplies are not damaged by static electricity.

In principle, electrostatic protection should be carried out from two aspects: controlling the generation of static electricity and controlling the dissipation of static electricity. Controlling the generation of static electricity mainly involves controlling the process and the selection of materials in the process; controlling the dissipation of static electricity mainly involves quickly and safely discharging and neutralizing static electricity. The combined effect of the two may result in the static electricity level not exceeding the safety limit, thus achieving the purpose of electrostatic protection.

In the production process, the core of electrostatic protection is to "eliminate static electricity". To this end, an electrostatic safety work area can be established, that is, by using various anti-static measures, the electrostatic voltage that may be generated in the area is kept below the threshold that is safe for sensitive devices. The substrate methods include:

1. Process control method:

Try to generate as little static charge as possible during the production process, and take measures from aspects such as process flow, material selection, equipment installation and operation management to control the generation and accumulation of static electricity, suppress the static electricity level and discharge capacity, and reduce its harm.

2. Release method:

The purpose of eliminating static electricity is to discharge it to the ground, such as adding anti-static agents or humidifying. The most common method is the anti-static belt and static grounding pole worn by the staff.

3. Electrostatic shielding method:

According to the principle of electrostatic shielding, it can be divided into internal field shielding and external field shielding. The specific measure is to use a grounded shielding cover to isolate the charged body from other objects, so that the electric field of the charged body will not affect other objects around it.

4. Composite neutralization method:

Usually, a grounding eliminator is used to generate ions with opposite charges to recombine with the charges on the charged body to achieve the purpose of neutralization and elimination.

5. Cleaning measures:

Cleaning measures are aimed at avoiding tip discharge. Keep the surface of the charged body and surrounding objects as smooth and clean as possible to reduce the possibility of tip discharge.

5 Determine the wire size

Below, let's take a look at the devices used in the above protection methods:

There are two main types of electrostatic protection equipment: antistatic products and static eliminators. Antistatic products are items made of antistatic materials. Their main function is to prevent or reduce the generation of static electricity and discharge the generated static electricity; while static eliminators are used to neutralize static electricity that accumulates on insulating materials and cannot be eliminated by discharge methods. There are many types of antistatic material products, but they can be mainly classified into the following categories:

1. Anti-static work clothes and wrist straps

Anti-static work clothing and wristbands are important components of the human body static electricity elimination system, which can eliminate or control the generation of human static electricity, thereby reducing the main source of static electricity in the manufacturing process of switching power supplies. Including anti-static suits, coats, shoes, hats, anti-static gloves, finger cots, etc. Anti-static clothing is made of anti-static cloth of different colors. The yarn in the cloth contains a certain proportion of conductive yarn, and the static electricity on the clothing is eliminated through the corona discharge and leakage of the conductive yarn. Anti-static wrist is the most important electrostatic protection product for operators when they come into contact with electronic components. Through the grounding path, the static electricity carried by the human body can be safely discharged. It consists of anti-static elastic band, movable snaps, spring soft wire, protective resistor and plug. It is most common on the switching power supply production line or other electronic equipment production factories.

2. Anti-static packaging and transportation products, etc.

There are many anti-static packaging products, such as anti-static shielding bags, anti-static packaging bags, anti-static sponges, anti-static IC packaging tubes, anti-static component boxes, anti-static bubble bags and anti-static transport carts, etc. The purpose is to protect the electronic components, switching power supply semi-finished products and power supply finished products from static electricity.

3. Anti-static floor and table mats

Anti-static floor and table mat are also indispensable in electrostatic protection projects. There are many kinds of anti-static floor, which are divided into permanent and temporary according to failure; conductive rubber, PVC and conductive ceramic according to material type; and direct ground laying and overhead raised floor according to laying method. You can flexibly decide to choose according to actual needs and cost.

4. Static eliminator (static eliminator, neutralizer or ion balancer)

Static eliminators are another large category of anti-static equipment besides anti-static material products. Their main principle is to use high-voltage electric fields or radioactive rays to locally ionize the air and generate a large number of ions and electron pairs. Among them, ions with opposite polarity to the charged body approach the charged body and neutralize it, thereby achieving the purpose of eliminating static electricity.

Understand the causes of static electricity and some static electricity protection measures. Start from the design and process flow, and use a comprehensive method to achieve better static electricity protection. Only then will the pass rate in the production process be higher and the quality of power supply products be more guaranteed!

qwqwqw2088

Anti-static is the most important thing in circuit design. If there is no anti-static measure in the circuit, it is a bit of a late repair in the later production links.

人去搂空

langtuodianzi

The switching power supply and its transient overvoltage protection design are also particularly important.