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Mindray sums up two common senses when customers purchase lead-free reflow
When it comes to choosing a lead-free reflow soldering system, customers often have specific concerns. In response, Mindray R&D engineers have compiled two key factors that consumers should consider when selecting the right reflow oven. These insights are based on the company’s extensive experience in reflow soldering technology.
First, the structure and temperature control of the reflow zones play a crucial role in the soldering process. Both traditional and lead-free reflow ovens typically use similar heating zone structures. Each zone is equipped with a motor-driven impeller that spins at high speeds to generate airflow. This air is heated by resistive elements or other materials and then blown through perforated plates onto the PCB. The motor speed in Mindray's reflow ovens is programmable, ranging from 1000 to 3000 RPM. The higher the speed, the stronger the airflow and the more effective the heat transfer.
However, during the reflow process, flux from the solder paste may evaporate and condense on the impeller, reducing its efficiency and affecting the temperature profile. Regular cleaning of the impeller is essential to maintain optimal performance. Additionally, each heating zone in the reflow oven is controlled by an independent closed-loop system using PID control. Temperature sensors, usually thermocouples mounted beneath the perforated plates, monitor the gas stream temperature and help maintain precise control.
If a zone fails to heat properly or heats too slowly, it could be due to a faulty solid-state relay, aging heater elements, or general wear and tear over time. If the temperature display shows errors, it might indicate damage to the thermocouple wire. These checks are important for ensuring consistent and reliable soldering results.
Second, the reflow curve is a critical factor influenced by the characteristics of the reflow oven. The reflow curve refers to the temperature profile that the PCB must follow during the soldering process. Different ovens have varying numbers of heating zones, air flow capabilities, and overall temperature capacities, all of which affect the final reflow curve.
The number of heating zones determines how precisely the temperature can be controlled. More zones allow for better adjustment of complex profiles, making them ideal for boards with dense components or high-volume production. On the other hand, fewer zones may limit the ability to create intricate curves, which could be a drawback for certain applications.
Airflow also plays a significant role. Most reflow ovens rely on fans to circulate hot air, and the fan speed directly impacts the temperature profile. Higher fan speeds increase airflow and, consequently, the reflow temperature. If a fan motor fails, the temperature curve may drop significantly, leading to issues like cold solder joints or poor cooling. Therefore, regular monitoring of fan speed is essential, especially in programmable systems.
Lastly, the furnace’s thermal capacity is another important consideration. Larger PCBs may require more heat to reach the desired temperature, and if the furnace lacks sufficient power or insulation, the temperature may drop during the process. Thermal capacity is determined by the oven’s design and heater power, which are fixed at the manufacturing stage. Choosing an oven with adequate thermal capacity ensures better performance, energy efficiency, and consistent soldering quality.
In summary, when selecting a lead-free reflow soldering system, understanding the structure, temperature control, airflow, and thermal capacity of the oven is essential. These factors not only influence the soldering outcome but also impact the efficiency and reliability of the entire production process.
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