At present, there is a lot of information about lead-free soldering materials and lead-free soldering processes. For factories that need to develop lead-free soldering processes, it is very important to select these information correctly and combine them organically. To develop a sound, high-quality lead-free soldering production line requires careful planning, and efforts to implement the plan and strict process monitoring to ensure product quality and keep the process under control. These controls are related to many changes, such as materials, equipment, compatibility issues, pollution issues, statistical process control (SPC) procedures, etc.
The use of lead-free soldering materials will have a serious impact on the soldering process. Therefore, in the development of lead-free soldering processes, all relevant aspects of the soldering process must be optimized. Georze Westby's five-step method for developing lead-free soldering processes helps lead-free soldering process development and process optimization.
1 Choose the appropriate materials and methods In the lead-free soldering process, the choice of soldering materials is the most challenging. For the lead-free soldering process, the selection of lead-free solder, solder paste, flux and other materials is the most critical and the most difficult. When choosing these materials, we must also consider the type of soldering components, the type of circuit board, and their surface coating conditions. The selected materials should be proven in their own research, or recommended by authoritative institutions or literature, or have been used in experience. List these materials for preparation in the process test, in order to conduct an in-depth study of them, to understand their impact on all aspects of the process.
For the soldering method, you should choose according to your actual situation, such as component types: surface-mounted components, through-hole plug-in components; circuit board conditions; the number and distribution of components on the board. For the soldering of surface-mounted components, reflow soldering is required; for through-hole plug-in components, wave soldering, dip soldering or spray soldering can be selected for soldering. Wave soldering is more suitable for welding of through-hole plug-in components on the whole board (large); dip welding is more suitable for welding of through-hole plug-in components on the whole board (small) or local areas on the board; local spray flux is more suitable Welding of individual components or a small number of through-hole components on the board. In addition, it should also be noted that the whole process of lead-free soldering is longer than that of leaded solders, and the required soldering temperature is higher. This is because the melting point of lead-free solders is higher than that of leaded solders, and its infiltration Sex is worse.
After the welding method is selected, the type of welding process is determined. At this time, it is necessary to select equipment and related process control and process inspection instruments according to the welding process requirements, or upgrade. The choice of welding equipment and related instruments is the same as the choice of welding materials, which is also very critical.
2 Determine the process route and process conditions After the first step is completed, the welding process test can be performed on the selected welding material. Determine the process route and process conditions through experiments. In the test, the welding materials selected in the list need to be fully tested to understand their characteristics and impact on the process. The purpose of this step is to develop samples for lead-free soldering.
3 Develop and improve the welding process This step is the continuation of the second step. It is to analyze the test data collected in the second step of the process test, and then improve the materials, equipment or change the process in order to obtain a sound process under laboratory conditions. In this step, it is also necessary to understand the possible contamination of the lead-free alloy welding process, know how to prevent it, determine the process capability (CPK) value of various welding characteristics, and compare it with the original tin / lead process. Through these studies, the inspection and test procedures of the welding process can be developed, and at the same time, some treatment methods for the process runaway can be found.
4. We also need to conduct reliability test on the welding samples to verify whether the quality of the products meet the requirements. If the requirements are not met, the cause must be found and resolved until the requirements are met. Once the reliability of the soldered product meets the requirements, the development of the lead-free soldering process is successful. This process is ready for large-scale production after the quasi-ready operation. Everything is ready, and it is now possible to switch from sample production to industrial production. At this time, the process still needs to be monitored to maintain the process in a controlled state.
5 Control and improve the process The lead-free soldering process is a dynamic stage. Factories must be alert to various problems that may arise to avoid process runaway. At the same time, they also need to continuously improve the process so that the quality and qualified crystal rate of products can be continuously improved. For any lead-free soldering process, improving the soldering materials and updating the equipment can improve the soldering performance of the product.
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