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 seen significant advancements, driven by evolving production standards, the introduction of new solder pastes, and the development of various substrates. Additionally, innovations in component design and materials have pushed the boundaries of heat treatment processes. The miniaturization of products has led to the emergence of new component packages such as BGA (Ball Grid Array), COB (Chip on Board), CSP (Chip Scale Package), MCM (Multi-Chip Module), and flip chips. These compact designs have resulted in smaller components with higher pin counts and finer pitches, making the reflow process more complex than ever before. To reduce costs, manufacturers are increasingly adopting no-clean and low-residue solder pastes, while also using nitrogen gas more frequently. This trend is largely driven by the growing demand for portable electronic devices, which require more compact, high-density, and lightweight assemblies. As product cycles shorten and I/O density increases, the need for precise and controllable reflow technology becomes even more critical. One of the key developments in this area is the use of nitrogen in the reflow process. Nitrogen provides an inert atmosphere that reduces oxidation, allowing for the use of less active solder paste. This is especially beneficial for low-residue and no-clean pastes, as well as for multi-pass reflow operations. For example, in double-sided PCBs with OSP (Organic Solderability Preservative) finishes, nitrogen protection ensures better solderability of copper pads. It also improves surface tension, giving manufacturers more flexibility when working with ultra-fine pitch components and enhancing the reliability of solder joints. While nitrogen usage comes with additional costs, its benefits in terms of yield improvement and quality control often outweigh these expenses. However, controlling nitrogen consumption remains a challenge, especially in forced convection reflow ovens where airflow is continuous. To manage this, manufacturers implement strategies like reducing furnace inlet size, using baffles or curtains to prevent nitrogen leakage, and designing chambers that take advantage of natural gas stratification. Another major development is the increasing use of double-sided reflow processes. While this approach offers greater design flexibility and cost efficiency, it also introduces challenges such as component shifting during the second reflow or partial melting of existing solder joints. Solutions include using components with different melting points or optimizing the weight-to-tension ratio to ensure stability. A general guideline is that components weighing up to 30g/in² can typically remain in place without falling during secondary reflow. As the industry moves toward higher-density and more complex boards, the reflow process will continue to evolve. With ongoing improvements in materials, equipment, and process control, the future of reflow soldering looks promising. **Technical Support:** [Http://news.chinawj.com.cn](http://news.chinawj.com.cn) Editor: Hardware Business Network Information Center

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