The chip transformer welding process is crucial in the manufacture of electronic equipment. Problems such as cold soldering and short circuits will not only lead to unstable component performance, but may even cause failures in the entire circuit system. To avoid these problems, it is necessary to systematically control multiple links such as preparation before welding, pad and component processing, solder paste selection and coating, welding temperature control, operator skill improvement, post-welding inspection and process optimization, and build a refined welding process by combining material properties and process principles.
Adequate preparation before welding is the basis for ensuring welding quality. First of all, it is necessary to conduct a comprehensive inspection of the welding equipment to ensure that the temperature control of tools such as reflow ovens and soldering irons is accurate, and the conveyor belt runs smoothly to avoid welding defects caused by equipment parameter deviations. At the same time, the chip transformer and PCB board to be welded should be cleaned, and impurities such as oxides, oil stains and dust on the surface of component pins and pads should be removed with anhydrous alcohol or special cleaning agents. These contaminants will hinder the effective wetting of solder and metal surfaces, resulting in cold soldering. In addition, according to the chip transformer size, pin spacing and PCB board design requirements, select a suitable welding process, such as reflow soldering or manual soldering. Different processes have significant differences in temperature and time requirements, and the process parameters need to be clarified and debugged in advance.
The pretreatment of pads and components directly affects the reliability of welding. The pad design of the PCB board should meet the standards to ensure that the pad size matches the pin of the patch transformer. Too large or too small pads may cause uneven solder distribution and increase the risk of cold soldering and short circuit. For components with fine pins or small spacing, high-precision processes such as laser etching can be used to process the pads to improve the flatness and consistency of the pads. In terms of component pin processing, if the surface plating of the pin is oxidized or damaged, secondary tinning treatment is required to form a uniform solder layer on the surface of the pin through tinning or tinning process to enhance the bonding strength between the pin and the solder paste. During the pretreatment process, the operating force must be strictly controlled to avoid damaging the component pins or PCB pads.
The selection and application of solder paste is a key link in the welding process. The composition, particle size and activity of solder paste directly affect the welding effect. The appropriate type of solder paste should be selected according to the chip transformer material and working environment, such as lead-free solder paste or silver-containing solder paste. Lead-free solder paste meets environmental protection requirements, but has a higher melting point and requires a higher welding temperature; silver-containing solder paste has excellent conductivity and is suitable for high-frequency or precision circuits. When applying solder paste, use a precision steel mesh printing process. The opening size and thickness of the steel mesh must match the component pins and pads to ensure that the amount of solder paste is uniform. During the printing process, control the pressure and speed of the scraper to avoid solder paste accumulation or tipping. For components with dense pins, step steel mesh or nano steel mesh technology can be used to improve the accuracy of solder paste coating and reduce short circuit problems caused by excessive solder paste.
Accurate control of welding temperature is the core of avoiding cold solder joints and short circuits. Taking reflow soldering as an example, a reasonable temperature curve needs to be set according to the melting point of the solder paste and the heat resistance of the component, usually including four stages: preheating, insulation, reflow and cooling. The temperature should be raised slowly during the preheating phase to allow the solvent in the solder paste to fully evaporate, avoiding solder paste splashing and thermal shock to components due to rapid evaporation of the solvent; the temperature should be kept stable during the insulation phase to fully activate the flux in the solder paste and remove oxides on the metal surface; the temperature should reach the melting point of the solder paste during the reflow phase to allow the solder to fully melt and wet the component pins and pads; the cooling rate should be controlled during the cooling phase to allow the solder joints to solidify quickly and form bright and full solder joints. Throughout the process, thermocouples and other temperature measuring tools are used to monitor the temperature in the furnace in real time to ensure that the temperature curve is consistent with the set value, to avoid component burning or excessive melting and flow of solder due to excessive temperature, or solder not completely melted due to low temperature to produce cold solder joints.
The skill level of the operator has a direct impact on the quality of welding. For manual welding scenarios, operators need to undergo professional training, master the correct method of holding a soldering iron with a pen, and control the contact angle and time between the soldering iron tip and the component pins and pads. When welding, the soldering iron tip should contact the pin and the pad at the same time to conduct heat evenly. After the solder paste melts, slowly remove the soldering iron to avoid sharp solder joints or pores. For the welding of tiny components or dense pins, a microscope can be used to assist the operation to improve the accuracy of welding. Operators are regularly organized to conduct skill assessments and experience exchanges, and share problems and solutions encountered during welding. For example, the problem of cold solder joints can be improved by increasing the amount of solder paste or adjusting the welding temperature. For short circuit problems, tin suction wire can be used to remove excess solder, which improves the operator's emergency handling ability and quality awareness.
Post-welding inspection is an important means to promptly detect cold solder joints and short circuit problems. A combination of visual inspection, AOI (automatic optical inspection) and X-ray inspection is used to conduct a comprehensive inspection of solder joints. Visual inspection mainly observes the appearance of solder joints, such as whether they are bright, full, and whether there are defects such as cracks and pores; AOI uses high-definition cameras and image processing technology to quickly detect the size, position and welding quality of solder joints, and can identify tiny cold solder joints and short circuits that are difficult to detect with the naked eye; X-ray inspection is suitable for detecting internal defects of hidden solder joints, such as cold solder joints under pads or insufficient solder filling. For detected bad solder joints, they need to be repaired in time, and components should be carefully removed using a hot air gun or special repair tools. After cleaning the pads, they should be re-welded. During the repair process, attention should be paid to controlling the temperature and time to avoid secondary damage to the PCB board and components.
Continuous process optimization is a long-term mechanism to improve welding quality. Regularly collect statistics and analyze the defective rate during the welding process, identify the main causes of cold solder joints and short circuits, such as uneven solder paste coating, unreasonable temperature curve settings, or insufficient operator skills, and take targeted improvement measures. For example, by introducing a fully automatic solder paste printer to improve coating accuracy, or working with solder paste suppliers to develop a more suitable solder paste formula; for the problem of cold solder joints caused by poor coplanarity of component pins, a pin leveling process can be added before welding. At the same time, pay attention to new technologies and processes in the industry, such as laser welding and ultrasonic welding. These new welding technologies have the advantages of precise heating and small heat-affected zone, which can effectively reduce welding defects and improve chip transformer welding reliability. By continuously optimizing the welding process and forming a PDCA (Plan-Do-Check-Act) cycle, the stability of the production process and product quality are continuously improved.
