SMT electronic components soldering process

IPC-9502, or Printed Wiring Board (PWB) assembly process guide for electronic components, is an important industry standard that provides key guidelines and specifications for the assembly and soldering process of electronic components. The following is a detailed explanation of the standard, including its main content and key points.

1. Overview of IPC-9502 IPC-9502 is a standard developed by the Electronic Circuits and Electronic Interconnections Industry (IPC) in the United States and promulgated in 1999. This standard sets out the constraints in the manufacturing welding process for components that comply with IPC-9501, IPC-9503, IPC-9504, and J-STD-020 to ensure that the components are not damaged during the welding process. It does not address the optimal assembly conditions, but rather gives a guide to ensuring the safe soldering of components.

2. Background and purpose of the standard The packaging technology of electronic components continues to evolve, from in-line to flat-mounted, the connection cable is replaced by FPC soft board, and the resistor capacitor of the components has undergone many generations, developing in the direction of 0201 flat-mount and BGA packaging. These changes all indicate that electronic technology is developing in the direction of miniaturization and miniaturization. Manual soldering is also more difficult, and the slightest negligence can damage components or lead to poor welding. Therefore, the formulation of IPC-9502 is extremely critical to ensure the quality of welding and the reliability of components.

3. Soldering principle and process Soldering is a science, the principle of which is to melt the solid solder wire by heating the soldering iron, and then use the role of flux to let the molten solder flow between the soldered metals, and form a stable and reliable soldering point after cooling. The soldering process mainly includes three physical and chemical processes: wetting, diffusion and metallurgical bonding: Wetting: The molten solder flows along the subtle concave and convex and crystallization gaps on the surface of the base metal with the help of capillary force, and then forms an adhesion layer on the surface of the welded base metal, so that the atoms of the solder and the base metal are close to each other to reach the distance where the atomic gravitational energy can work. The environmental conditions that cause wetting are that the surface of the base metal to be welded must be clean and free of oxides or contaminants. Diffusion: As wetting progresses, the inter-diffusion between the atoms of the solder and the base metal begins to occur. The atoms are in a state of thermal vibration in the lattice lattice, and the atomic activity intensifies when the temperature rises, causing the atoms in the molten solder and the base metal to cross the contact surface into each other's lattice lattice. The speed and number of atoms moving depends on the temperature and time of heating. Metallurgical bonding: Due to the diffusion of the solder and the base metal, an intermediate layer – a metal compound – is formed between the two metals. In order to obtain a good solder joint, a metal compound must be formed between the welded base metal and the solder, so that the base metal can achieve a strong metallurgical bond.

Fourth, the role of flux Flux plays an indispensable role in the soldering process. Its main functions are as follows: Chemical activity: There are many forms of chemical reactions between flux and oxide, including mutual chemical reaction to form a third substance, the reduction of oxide to metal, and the simultaneous existence of the above two reactions. A typical first reaction is the removal of the oxide layer by rosin flux, which reacts with copper oxide to form copper rosin, which is then removed along with the rosin. Prevent re-oxidation: While removing the oxide reaction, the flux must also form a protective film to prevent the surface of the solder from being oxidized again until it comes into contact with the solder. Other features: The flux must also be able to withstand high temperatures without decomposing or evaporating at the temperature of the soldering operation. If it decomposes, it will produce solvent insoluble substances that are difficult to clean with solvents.

5. Interpretation of IPC-9502 key contents IPC-9502 as a guide to the PWB assembly soldering process of electronic components, covers a number of key aspects, and the following is a detailed interpretation of its main contents:

1.Preparation before welding Before welding, a series of preparations need to be carried out to ensure that the welding process goes smoothly and ensures the quality of welding. Cleaning: The surface of the welded base metal must be clean and free of oxides, contaminants or other impurities. This can be achieved through the use of cleaning agents, ultrasonic cleaning, etc. Flux selection: Select the appropriate flux according to the soldering material and soldering conditions. When selecting a flux, consider factors such as its chemical activity, thermal stability, and the effect of residues on the solder joint. Preparation of soldering iron: The soldering iron tip should be clean, without oxidation, hook deformation and other problems. The selection of soldering iron tips is determined according to the type and thickness of the soldering material. At the same time, the temperature of the soldering iron should be controlled within a suitable range to ensure the quality and efficiency of soldering.

2.Welding Process Control The welding process is one of the key focuses of IPC-9502. During the welding process, various parameters and conditions need to be strictly controlled to ensure the quality of the weld and the reliability of the components. Welding temperature and time: The welding temperature and time should be determined according to the type, thickness and welding requirements of the welding material. Generally speaking, the soldering temperature should be controlled above the melting point of the solder wire, but it should not be too high, so as not to damage the components or cause poor soldering. The welding time should be as short as possible to reduce thermal stress and thermal damage. Soldering pressure: Appropriate pressure should be applied when the tip is in contact with the weldment to promote the wetting and diffusion of the solder. However, the pressure should not be too large, otherwise it will damage the components or cause deformation of the solder joint. Soldering position and quantity: The solder wire should be supplied close to the pad to ensure that the solder can be evenly covered on the pad. The supply quantity should be determined according to the size of the pad and the soldering requirements. At the same time, the soldering iron tip should be in contact with the two weldments to be connected to each other at the same time to prevent false soldering or poor soldering.

3.Post-Welding Inspection and Testing After welding, a series of inspections and tests are required to ensure weld quality and component reliability. Visual inspection: Check the appearance of the weld joint by visual inspection or a tool such as a magnifying glass to ensure that the weld joint is smooth, free of cracks, no porosity and other defects. Electrical performance test: Use test instruments to test the electrical properties of the welded joint, such as resistance test, insulation resistance test, etc., to ensure that the electrical performance of the weld joint meets the requirements. Reliability test: Reliability evaluation of welded components is carried out with the help of reliability test methods such as thermal cycling test and vibration test. These tests simulate the forces of a component in a real-world use environment to evaluate its reliability and durability.

4.Special Welding Requirements For some special welding requirements, IPC-9502 also gives corresponding guidelines and specifications. Lead-free soldering: With the improvement of environmental awareness and the development of lead-free trends, lead-free soldering has become an important trend in the assembly of electronic components. IPC-9502 provides requirements and guidance for lead-free soldering, including the selection of lead-free solder, and the control of soldering temperature and time. High-density assembly: With the development of electronic component packaging technology and the improvement of PCB board density, high-density assembly has become an important direction of electronic component assembly. IPC-9502 provides requirements and guidance for high-density assembly, including the layout of weld joints, control of the welding process, and more. Soldering of micro-miniature components: For the soldering of micro-components, IPC-9502 also gives corresponding requirements and guidance. These requirements include the control of the welding temperature, the adjustment of the welding pressure, etc., to ensure that the micro-small components are not damaged during the welding process and that the welding quality is good.

6. Links between IPC-9502 and other relevant standards There is a close correlation and complementarity between IPC-9502 and other relevant standards. Together, these standards form a complete specification system for the assembly and welding of electronic components. IPC - 9501: This standard provides general requirements and guidance for the assembly and soldering of electronic components. It covers the selection of welding materials, the control of the welding process, and the inspection and testing after welding. IPC-9502 complements and refines IPC-9501 and provides more specific welding process requirements and limitations. IPC - 9503: This standard regulates reliability issues during the assembly and soldering of electronic components. It provides reliability testing methods and evaluation criteria to ensure the reliability and durability of welded components in the actual use environment. IPC-9502 also emphasizes reliability requirements in the welding process and complements IPC-9503. IPC - 9503: This standard regulates quality issues in the assembly and soldering of electronic components. It provides quality inspection methods and evaluation criteria to ensure that the quality of welded components meets the requirements. IPC-9502 also emphasizes the importance of quality inspection in the welding process and complements IPC-9504. J - STD - 020: This standard is a specific requirement and specification for the soldering process of electronic components. It covers the selection of welding materials, the control of the welding process, and the inspection and testing after welding. IPC-9502 and J-STD-020 overlap and complement each other in terms of soldering process, and together constitute a complete specification system for the soldering process of electronic components.

7. Application and significance of IPC-9502 IPC-9502 has a wide range of applications and important significance in the electronics manufacturing industry as a guide to the soldering process of PWB assembly of electronic components. Improved Weld Quality: By tightly controlling the various parameters and conditions in the welding process, IPC-9502 can significantly improve weld quality and reduce weld defects and failure rates. Enhance component reliability: IPC-9502 emphasizes reliability requirements in the welding process and evaluates welded components through methods such as reliability testing. This helps to improve the reliability and durability of the components in the real-world use environment. Promote standardization and standardization: IPC-9502 is an industry standard that provides uniform specifications and guidance for the assembly and soldering of electronic components. This helps to promote the standardization and normalization of the electronics manufacturing industry. Promoting technological innovation and progress: The development and implementation of IPC-9502 requires continuous technological innovation and progress. At the same time, it also points out the direction and provides impetus for technological innovation and progress. Through continuous improvement and optimization of the welding process and technical level, it can promote the continuous development and progress of the electronics manufacturing industry.

8. Conclusion IPC-9502 is an important process guidance document, which provides detailed guidance and specifications for the PWB assembly and welding process of electronic components. Strict compliance with IPC-9502 regulations and requirements can ensure the integrity and reliability of electronic components during PWB assembly and soldering, thereby improving the quality and reliability of products. At the same time, IPC-9502 also provides an important reference and basis for the optimization and improvement of the welding process, which helps to promote the continuous development and progress of electronic component packaging technology and welding technology.

The importance of IPC-9502 in the electronics manufacturing industry cannot be overlooked. It specifies in detail the soldering process of PWB assembly of electronic components from many aspects, including preparation before soldering, soldering process control, post-soldering inspection and testing, special soldering requirements, etc., each link has specific operation points and considerations. In association with other relevant standards, it complements and relates with IPC-9501, IPC-9503, IPC-9504 and J-STD-020 to build a complete specification system for the assembly and welding of electronic components. Its application significance is reflected in improving welding quality, enhancing component reliability, promoting standardization and normalization, and promoting technological innovation and progress. In conclusion, IPC-9502 is a key standard in the electronics manufacturing industry to ensure the high quality and reliability of the PWB assembly soldering process, providing a solid foundation and clear direction for the development of the industry.