Requirements of reliable performance of DC-DC module power supply on production environment
In the modern high-tech era, the higher the reliability of DC-DC power modules, but AC-DC power conversion and DC-DC power conversion have gradually become the module or integrated chip industry, and also gradually become an important part of various electronic equipment and industrial automatic control equipment. The quality and reliability of AC-DC power modules and DC-DC power modules also greatly affect the reliability, failure efficiency and maintenance rate of the whole equipment.
The reliability of power supply products is affected by design, process, management, testing and means, incoming materials and other factors, which are the concerns of manufacturers and users of power supply modules. In fact, the reliability of the power module should not only ensure the optimization of various performance indicators, but also ensure that the production environment of the power module is clean and orderly, with good electrostatic protection measures and appropriate temperature and humidity. Only under such conditions can the power module be truly called a reliable power product. With the continuous progress of society, electronic equipment is playing an increasingly important role in industrial production, transportation, communications and other fields. The reliability of electronic equipment also determines the effective operation of various economic activities to a certain extent. Although the cost of power module in electronic equipment is very low, it can be called the "heart" of electronic equipment. The failure of power module may directly lead to the paralysis of electronic equipment, Causing irreparable losses.
1、 Electrostatic protection: during the manufacturing, storage, transportation and assembly of components, due to the relative movement of instruments, materials and operators, electrostatic voltage may be generated due to friction. When the components are in contact with these charged bodies, the charged bodies will discharge through the devices, causing device failure. Most modern integrated circuits use MOS circuits, and most power modules also use MOS tubes and integrated circuit chips. In the production of the power module, if we do not pay attention to electrostatic protection, it will often lead to a high component failure rate. Even if the product passes the test, it may cause slight damage to the MOS tube and integrated circuit chip due to static electricity during the manufacturing process, thus affecting the service life and reliability of the power module. The introduction of electrostatic protection system in the production environment (such as anti-static grounding of human body, anti-static grounding of ground and anti-static grounding of operating devices and instruments) can effectively avoid damage to MOS tubes and integrated circuit chips. Anti static damage of electronic components is a complex system engineering, which runs through the whole process of system or equipment development and production. From the procurement, packaging, transportation, inventory, installation, commissioning, testing of components to the use of users, the whole process, all-round and all personnel shall follow a series of relevant measures to prevent electrostatic loss. Protection is a systematic project, which requires the input of equipment, personnel and effective management and system. It can be seen that the quality of an electrostatic protection system directly reflects the quality management level of an enterprise and shows the strength of an enterprise.
2、 Humidity: moisture can penetrate into porous materials, causing leakage paths between conductors and generating oxygen. Moisture absorption of parts and components will reduce insulation resistance and isolation and voltage resistance. However, excessive drying can also make some materials brittle, rough surface, and even generate static electricity. Therefore, the production environment will also have a certain impact on the reliability of the power supply. Most power modules are produced by soldering components on small PCB boards (printed circuit boards), and then pouring small PCB boards into the shell with resin. In the production process, if the humidity of the production environment is high, especially in the rainy season in the south, the moisture in the air will condense on the PCB board and components. Even if the bubbles are removed by the vacuum defoaming process when the resin is used for potting, the moisture on the PCB board and components cannot be removed. When the power module works at a high ambient temperature, the moisture on the PCB board and components will vaporize and expand, resulting in cracks in the power module, breaking the internal transformer wire, or introducing external moisture, corroding the components inside the power module or causing short circuit in the circuit inside the module. For the occasions with high isolation voltage requirements, the moisture on the PCB board and components will also reduce the isolation capability of the power module, and even cause the first inter stage breakdown, with serious consequences. Too low humidity will also cause too much dust floating in the air, affecting the quality of the power module. Too low humidity will also generate electrostatic charges due to personnel walking. Even if protected by the electrostatic protection system, it may cause electrostatic damage or soft breakdown of components, resulting in the same consequences as described above. The introduction of air conditioning system and dehumidification system in the production environment can keep the humidity of the production environment at an appropriate level, and avoid adverse effects on the reliability of the power module due to moisture condensation or excessive drying of the air. Influence of humidity on the product: moisture in the air is immersed in the resin. At the initial stage of heating, a small amount of water vapor pressure causes delamination of the resin interface. The pressure of water vapor increases with the welding temperature, causing the resin to expand, and the water vapor is discharged through the package crack, creating a bad product phenomenon.
3、 Temperature: the temperature of the production environment also needs to be strictly controlled. High temperature and low temperature will have different effects on components.
3.1 high temperature and high temperature environment will change the resistance, inductance, capacitance, electric power series and other electrical performance parameters in the power supply, making the insulator soft and causing insulation failure; The active element may cause structural failure due to expansion jamming, blistering on the coating surface, acceleration of oxidation and other chemical reactions, reduction of lubricant viscosity and evaporation, and loss of lubricity; The wear of the moving parts increases due to physical expansion and the structural strength decreases.
3.2 low temperature and low-temperature environment will make the plastic and rubber of the power supply lose flexibility and become brittle. When there is moisture, ice will appear, and the lubricant will become colloid and become sticky and lose lubricity; The coating surface is cracked; Structural failure due to physical shrinkage, change of electrical and mechanical functions, etc.
3.3 the temperature control power supply module, especially the small-sized 1W and 2W power supply modules, often adopts the magnetic ring winding transformer with the inner diameter less than 5mm. The winding of this type of transformer can only be produced manually. When the production temperature is high, the palms of the production staff will sweat. When the transformer is wound, the sweat on the hands will stay on the transformer, and the moisture and salt in it will damage the paint skin of the transformer and reduce the insulation capacity of the transformer, Which may have a potential impact on the reliability of the power module. The air conditioning and temperature control system shall be installed in the production workshop to ensure that the temperature of the workshop is maintained at about 26 degrees, so that the production staff can have a cool and comfortable environment, and only then can the power module products with reliable quality be produced.
4、 Dust: more dust will scratch the power supply, wear the finishing surface, cause air hole blockage, lubricant pollution, insulation pollution, generate corona path, and reduce electrical performance. If the production environment is not clean and the dust floating in the air falls on the PCB board, the false soldering and false soldering of components will be greatly increased, which will not only affect the production qualification rate of products, but also affect the reliability and service life of products. Paying attention to the cleaning of the production environment and doing well in 5S management is a guarantee to ensure the production of qualified and reliable products. The sand and dust in the north are more severe than those in the south, so more attention should be paid to control, and air filtration, sealing, smoke exhaust system and other methods can be adopted to solve the problem.
5、 Storage and safekeeping: improper storage and safekeeping is another important reason for the reliability reduction or failure of components, which must be paid attention to and corresponding measures taken. If the temperature and humidity of the warehouse should be controlled within the specified range, use a moisture-proof box, pay attention to moisture-proof and anti-static, do not allow harmful gases to exist, and regularly recheck. Containers for storing components shall be made of materials that are not easy to carry static electricity and cause chemical reaction of components. Sensitive components shall be regularly inspected. Electronic raw materials should also be handled and handled with care. Ceramic capacitors, magnetic materials and other raw materials are easy to fall and crack, and special attention should be paid to their use and handling.