Introduction
In modern electronics manufacturing, reflow soldering oven is a key step in the SMT assembly line. It directly affects the quality of soldering between electronic components and PCB, and one of the most central factors is – temperature control.
In this paper, we will discuss the importance of temperature control in the reflow process, and how to do a good job of temperature control, to help you enhance the productivity of the SMT assembly line.
I. What is reflow oven?
Reflow oven is a kind of heating to make the solder paste melting, so as to realize the components and PCB pads to form a solid electrical connection between the process. The whole process is usually divided into four main stages:
- Preheat Zone: The temperature gradually rises in preparation for subsequent soldering.
- Soak Zone: Further heating, so that the solder paste to reach the melting point, and begin to dissolve.
- Reflow Zone: Temperature control in this zone is critical to ensure that solder joints are formed completely and evenly.
- Cooling Zone: A cooling zone where the solder joint cools and solidifies quickly to form a stable solder structure.
Each stage of the temperature has specific requirements, any part of the temperature deviation may lead to welding defects, affecting the reliability of the final product.
II. Why is temperature control so important?
1. Preventing false or cold soldering of welded joints
Insufficient or uneven temperature distribution can lead to incomplete melting of the solder, resulting in false or cold soldering and affecting the reliability of the electrical connection.
Accurate temperature control ensures that the solder fully wets the pads and prevents such defects.
2. Avoid component damage
Some sensitive components (such as IC, LED, etc.) are very sensitive to high temperatures. If the temperature is too high or the holding time is too long, the internal structure of the component may be damaged, or even burned out.
3. Control Solder Ball and bridging
Excessive heating rates or localized high temperatures can lead to splattering of solder paste, formation of solder balls or bridging of adjacent solder joints.
Segmented temperature zone design (preheating rate <2 / s) can stabilize the flux evaporation, reducing the risk of splattering.
4. Improve yield and consistency
Good temperature control can ensure that each piece of PCB soldering effect is consistent, reduce human debugging and post-testing costs, improve overall production efficiency and pass rate.
III. The temperature control points of the reflow oven
| Area | Temperature Range (℃) | Main Role | Control Points |
| Preheating zone | 50 – 150 | gradually heating, activation of flux | Rising temperature rate should not be too fast to avoid local overheating lead to deformation |
| Constant temperature zone | 150 – 180 | Uniform temperature, remove the solvent of the solder paste | Time control in 60-90 seconds is appropriate |
| Reflow zone | 210 – 260 (peak) | Solder paste melts, forming solder joints | The peak temperature should be higher than the melting point of the solder paste, but not exceeding the component tolerance limit. |
| Cooling zone | Drop to about 75 or less | Solder joints solidify | Rapid cooling helps to form a good crystalline structure |
Note: Different types of solder paste (such as lead-free solder paste Sn96.5Ag3.0Cu0.5) on the temperature profile requirements are slightly different, should be adjusted according to the specific material.
IV. How to optimize the reflow oven temperature control?
1. Set the appropriate reflow temperature curve: According to the parameters provided by the solder manufacturer and the heat resistance of the components, set the appropriate reflow temperature curve.
2. Real-time temperature monitoring: Through the thermocouple and other temperature sensors to monitor the temperature in the reflow oven in real time to ensure the accuracy of the temperature.
3. Regular maintenance: Regular cleaning and maintenance of the reflow oven to maintain its stable performance.
V. Common Problems and Solutions
| Problem | Possible cause | Solution |
| Void soldering | Temperature is too low, the temperature is too slow | Increase the peak temperature, speed up the rate of temperature rise |
| Solder ball | Uneven heating, solder paste spattering | Adjust the time of the constant temperature zone, optimize the solder paste printing |
| Component damage | Too high peak temperature | Lower the maximum temperature, shorten the high temperature residence time |
| Bridging | Too much solder paste or uneven reflow | Improve stencil design, optimize reflow profile |
Summary
Reflow soldering machine as the core of the SMT process, its temperature control directly affects the soldering quality and long-term stability of electronic products. An accurate and stable temperature profile not only improves product yield, but also extends the service life of the equipment and reduces maintenance costs.
Company profile
Zhejiang NeoDen Technology Co., LTD., founded in 2010, is a professional manufacturer specialized in SMT pick and place machine, reflow oven, stencil printing machine, SMT production line and other SMT Products. We have our own R & D team and own factory, taking advantage of our own rich experienced R&D, well trained production, won great reputation from the world wide customers.
We believe that great people and partners make NeoDen a great company and that our commitment to Innovation, Diversity and Sustainability ensures that SMT automation is accessible to every hobbyist on everywhere.
Post time: May-23-2025