What is Reflow Oven?

Introduction

In the field of electronic device manufacturing, reflow oven is a highly efficient and stable surface mount technology widely used in the production process of various electronic products.

Today, we will delve into what solder reflow oven is, understand its basic principles, process flow, and key parameters, and master the fundamentals of SMT technology.

I. Basic Definition of Reflow oven

Reflow oven is a soldering process that melts solder paste through heating to securely weld surface-mount devices (SMDs) to printed circuit boards (PCBs). It serves as the “thermal processing” stage in the SMD production line, typically positioned after the pick and place machine and before the SMT AOI machine.

II. What is the temperature range for the reflow oven?

During the entire reflow soldering process, the PCB is heated in a controlled manner, undergoing several critical stages.

1. Preheat Zone

• Purpose: The first stage of reflow soldering oven, where the temperature of the entire component assembly board is gradually raised to the target preheat temperature. This primarily ensures that the component assembly board can safely and gradually reach the pre-reflow temperature and allows volatile solvents in the solder paste to vaporize and evaporate.
• Temperature Range: Ambient Temperature → Approximately 150°C
• Characteristics: Avoids solder paste splattering or cracking caused by rapid temperature increases.

2. Soak Zone

• Purpose: Removes volatile substances from the solder paste and activates the flux, which begins to undergo oxidation-reduction reactions on the component leads and pads.
• Temperature Range: Approximately 150°C → 180°C
• Features: Excessively high temperatures may cause solder splatter, solder balls, or solder paste oxidation. Excessively low temperatures may result in insufficient flux activation. At the end of the soak zone, just before entering the reflow zone, the ideal condition is for the entire component assembly to have achieved balanced thermal equilibrium.

3. Reflow Zone

• Purpose: The solder paste fully melts in this stage, forming an alloy layer to achieve solder joint connection.
• Temperature Range: Up to 245°C (depending on the type of solder paste)
• Characteristics: This is the most critical stage. Excessively high temperatures may damage components, while excessively low temperatures may prevent proper solder joint formation.

4. Cooling Zone

• Purpose: The processed component assembly board gradually cools and solidifies at the solder joints.
• Temperature Change: From the peak temperature to below approximately 100°C
• Characteristics: Cooling speed affects joint structure and reliability.

III. How many types of reflow ovens are there?

Based on different heating methods, reflow ovens can be categorized into the following mainstream types.

IV. Key Parameters and Considerations for SMT Reflow Oven

To achieve high-quality soldering results, the following parameters must be precisely controlled.

• Peak Temperature: Determines whether the solder paste is fully melted.
• Ramp Rate: Affects flux activity and component heat resistance.
• Time Above Liquidus: The time the solder paste remains in a liquid state. Too short may prevent proper wetting, while too long may damage components.  
• Cooling Rate: Affects the crystalline structure of the solder joint. Too slow may cause cold solder joints.
• PCB design rationality (e.g., copper foil distribution, heat dissipation balance).
• Solder paste printing quality (thickness, position, coverage).
• Component temperature rating (especially sensitive components like BGA and QFN).

V. What is the purpose of a reflow oven in SMT?

In a complete PCB manufacturing line, PCB reflow oven occupies a central position.

• Pre-process: Solder paste printer → SMT SPI machine → Component placement by SMT machine
• Main process: Reflow oven completes the soldering
• Post-process: AOI inspection → Functional testing → Final inspection

It can be said that without a proper reflow soldering process, even the most precise component placement cannot be converted into reliable electronic products.

VI. What does a reflow oven do?

1. Electronic manufacturing

In the field of electronic manufacturing, reflow soldering technology is widely used for connecting various electronic components. This technology precisely controls the temperature and time of the soldering process, ensuring the quality and reliability of solder joints, thereby significantly enhancing the overall performance of electronic products. It also perfectly aligns with the trend toward increasingly miniaturized and high-performance electronic products.

2. Automotive electronics industry

Given the stringent requirements for welding stability and reliability in automotive electronics, reflow soldering technology provides stable and high-quality welding results, offering a robust technical foundation for the safety and stability of automotive electronic products.

3. Aerospace

The aerospace industry imposes extremely high demands on the performance and stability of electronic devices. Reflow soldering technology is widely applied in critical systems such as satellite navigation and flight control, playing an indispensable role in ensuring aviation safety.

4. New Energy Industry

With the rapid development of new energy technology, reflow soldering technology has also demonstrated significant potential in the solar and wind energy sectors. In the manufacturing of solar panels, the efficient and precise soldering capabilities of reflow soldering technology have significantly improved the energy conversion efficiency and service life of solar panels, injecting strong momentum into the sustainable development of the new energy industry.

VII. How to Optimize the Reflow Soldering Process?

For SMT factories, optimizing the reflow soldering process can be approached from the following aspects.

• Use professional reflow oven temperature measurement instruments: Monitor and adjust temperature curves in real time.
• Set scientific reflow oven temperature curves and conduct regular real-time tests of temperature curves.
• Solder according to the soldering direction specified in the PCB design.
• Prevent conveyor belt vibrations during the soldering process.
• Inspect the soldering results of the first PCB.
• Regularly maintain the reflow oven. Due to prolonged machine operation, organic or inorganic contaminants such as resin may accumulate and solidify. To prevent secondary contamination of PCBs and ensure smooth process implementation, regular maintenance and cleaning are necessary.

VIII. What is the difference between a reflow oven and wave soldering machine?

1. Principles

Wave soldering machine: Wave soldering involves spraying molten soft solder to form a solder wave. The PCB, pre-mounted with components, is then passed through the solder wave to achieve mechanical and electrical connections between the component terminals or leads and the PCB pads. During this process, the high-temperature liquid tin maintains an inclined surface, and a special device causes the liquid tin to form wave-like patterns, hence the name “wave soldering machine.”

Reflow oven: In reflow oven, solder paste is pre-applied to the pads before soldering. Then, high-temperature hot air melts the solder paste, connecting the component leads or terminals to the pads. This welding method utilizes the effect of hot airflow on the solder joints, causing the paste-like solder paste to undergo a physical reaction under a certain high-temperature airflow to achieve the welding objective.

2. Welding Methods

Wave soldering machine: Wave soldering involves forming molten solder into a solder wave, then passing the components through the wave for welding. This method is suitable for through-hole electronic components, whose leads are upright and require connection to the pads via the solder wave.

Reflow oven: Reflow oven uses high-temperature hot air to melt the solder, connecting the solder joints to the pads. It is primarily suitable for surface-mount electronic components, whose leads or solder terminals are flat and can directly contact the pads.

3. Applicable components

Wave soldering machine: Due to its soldering method, wave soldering is more suitable for soldering through-hole electronic components, especially those that require solder waves to connect to the pads.

Reflow oven: Reflow oven is more suitable for soldering surface-mount electronic components, as this method effectively achieves electrical interconnection between the components and the pads.

Conclusion

As the most critical step in the SMT process, reflow oven is both a technical challenge and a key factor in ensuring quality. Understanding its working principles, equipment types, and control points can not only help you better manage your SMT production line but also effectively improve product yield and customer satisfaction.

If you are planning an SMT workshop, upgrading your soldering process, or need a customized SMT solution, please contact our professional team for comprehensive technical support and  equipment services!

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.

In this decade, we independently developed NeoDen4, NeoDen IN6, NeoDen K1830, NeoDen FP2636 and other SMT products, which sold well all over the world. So far, we have sold more than 10,000pcs machines and exported them to over 130 countries around the world, establishing a good reputation in the market. In our global Ecosystem, we collaborate with our best partner to deliver a more closing sales service, high professional and efficient technical support.