A reflow soldering oven mainly consists of an airflow structure, heating system, transmission system, cooling system, nitrogen system, flux exhaust recovery system, exhaust system, and top cover lifting system. Its primary function is to complete the soldering of SMT components to the PCB, with advantages such as easy temperature control, oxidation prevention, and controllable cost.
1. Structural Components of a Reflow Soldering Oven
Airflow Structure
The airflow structure design varies among manufacturers. Common designs include vertical airflow, horizontal airflow, large return air, and small return air. Different airflow patterns affect temperature uniformity and the direction of hot air flow inside the oven, which directly influences soldering quality. A well-designed airflow system distributes heat more evenly across the PCB, avoiding local overheating or cold spots and ensuring soldering consistency.
Heating System
The heating system consists of a hot air motor, heating tubes or heating plates, thermocouples, solid-state relays, and a temperature control unit. The hot air motor drives hot air circulation, the heating elements generate heat, and the thermocouples measure temperature. The solid-state relays control the switching of the heating elements, while the temperature control unit regulates their operation based on thermocouple feedback. This allows precise control of the oven temperature according to a preset temperature profile.
Transmission System
The transmission system moves the circuit board from the reflow oven entrance to the exit at a controlled speed. It includes guide rails, a mesh belt or center support, chains, a drive motor, rail width adjustment, and speed control. Common transmission methods are chain plus mesh belt, and chain plus center support. Chain plus mesh belt ensures board stability during transport, while chain plus center support provides better support for large boards and prevents warpage. For non-standard guide rails, custom mesh belts, or precision center support components required for special board sizes, Hansheng Automation can provide custom machining based on customer drawings.
Cooling System
The cooling zone is located after the heating zones and rapidly cools the soldered PCB. Cooling can be air-cooled or water-cooled, depending on equipment configuration. Cooling speed and time must match the temperature profile and the cooling device. Rapid cooling solidifies solder joints quickly, improving joint strength and reliability. Air cooling is generally sufficient for standard electronics, while water cooling may be chosen for lead-free nitrogen-protected soldering.
Nitrogen System
Nitrogen protection has been used in reflow soldering for a long time and is widely applied. Full-process nitrogen protection in the preheat, soldering, and cooling zones prevents oxidation of solder joints and copper foil at high temperatures, improves wetting of the molten solder, reduces internal voids, and enhances solder joint quality. In lead-free soldering, nitrogen protection can lower the soldering temperature and reduce thermal damage to components while improving reliability.
Flux Exhaust Recovery System
This system usually includes an evaporator that heats flux volatiles above 450°C to gasify them. A water chiller circulates cooled water through the evaporator, and the gas is drawn out by an upper fan, condensed into liquid, and collected in a recovery tank. This reduces environmental pollution from flux exhaust and allows flux recovery, lowering production costs.
Exhaust System
Forced extraction ensures effective flux emission. A specialized exhaust filtration system keeps the working environment clean and reduces contamination of exhaust ducts. A good exhaust system removes flux fumes from the oven promptly, preventing their accumulation and protecting both soldering quality and the workspace.
Top Cover Lifting System
The upper furnace body can be opened as a whole for easy cleaning and maintenance. When internal cleaning or removal of a dropped board is needed, the operator activates the lift switch, and a motor drives the lifting rod. Limit switches stop the movement at the upper and lower positions. This design improves equipment maintainability and availability.
2. Functions of a Reflow Soldering Oven
Soldering Function
In the SMT process, the reflow oven receives PCBs with placed components and passes them through heating, soaking, soldering, and cooling stages. Solder paste changes from paste to liquid under high temperature and then solidifies after cooling, completing the soldering of SMT components to the PCB and forming reliable electrical and mechanical connections.
Temperature Control Function
The core of reflow soldering is using an external heat source to melt the solder and allow it to reflow and wet the joints. Reflow ovens have developed into various types, including vapor phase, infrared, far infrared, infrared hot air, full hot air, and water-cooled designs. A key capability is precise temperature control. By setting an appropriate temperature profile according to soldering requirements and solder characteristics, the oven maintains accurate and stable temperatures throughout the process, protecting temperature-sensitive components from overheating damage.
Oxidation Prevention Function
Through devices such as the nitrogen system, the reflow oven provides inert gas protection during soldering. This prevents oxidation of solder joints and copper foil at high temperatures, improves the wetting ability of molten solder, reduces internal voids, and raises solder joint quality. In lead-free soldering, nitrogen protection is especially effective in preventing reactions between solder joints and oxygen.
Cost Control Function
Reflow soldering offers easy temperature control and oxidation prevention, which also makes manufacturing costs easier to manage. Solder paste is pre-applied to the PCB pads in the correct amount and pattern, SMT components are placed on the paste, and the board enters the reflow oven for soldering. Precise temperature control and oxidation prevention reduce soldering defects, improve production efficiency, and lower overall manufacturing costs.
