Discussion on the development of reflow soldering process (1)

**Discussion on the Development of Reflow Soldering Process** In recent years, Surface Mount Technology (SMT) has experienced significant advancements. These changes are driven by evolving production standards, the introduction of new solder pastes, and the development of different substrates and component designs. As a result, heat treatment processes have also evolved to meet the demands of modern electronics. The miniaturization of products has led to the use of advanced component packages such as BGA (Ball Grid Array), COB (Chip on Board), CSP (Chip Scale Package), MCM (Multi-Chip Module), and flip chips. These components are smaller, with higher pin counts and finer pitches, which increases the complexity of the reflow process. To reduce costs, no-clean and low-residue solder pastes are becoming more popular. Additionally, the use of nitrogen in reflow ovens is increasing due to its ability to minimize oxidation during soldering. This not only improves solder joint quality but also supports the use of less active solder pastes, especially for low-residue and no-clean applications. Nitrogen also enhances surface tension, allowing for better control over fine-pitch components and improving the reliability of solder joints. While nitrogen offers many benefits, it also comes with cost considerations. The amount of nitrogen used depends on factors like machine design, location, and availability. Some manufacturers are exploring ways to reduce nitrogen consumption by optimizing furnace design or using solder pastes that require lower nitrogen concentrations. Although nitrogen can be seen as an added cost, its long-term benefits in terms of yield and quality often make it a worthwhile investment. Another key development is the growing adoption of double-sided reflow processes. This technique allows for greater PCB utilization and reduced manufacturing costs. However, it presents challenges, such as the risk of components falling off during the second reflow or partial melting of existing solder joints. Solutions include using components with specific size constraints, selecting solder pastes with different melting points, or applying cold air to the bottom of the board during the second reflow to prevent overheating. The relationship between component weight and solder joint surface tension plays a crucial role in determining whether components will stay in place during secondary reflow. A standard value of 30g/in² is often used as a conservative design guideline to ensure stability without requiring extensive testing for each component. As technology continues to advance, reflow soldering will need to adapt to even higher levels of density and complexity. With ongoing improvements in process control, equipment design, and material science, the future of reflow soldering looks promising. **Technical Support:** Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn

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