PCBA Tech - What are the types of SMT processing reflow ovens

Reflow oven is the main soldering equipment in PCB assembly. Soldering is one of the most critical processes in SMT. The performance of the equipment has a direct impact on the quality of soldering. In particular, the current lead-free soldering has the characteristics of high temperature, poor wettability, and small process window. Lead-free reflow oven selection should be more cautious. There are many types of reflow ovens, such as hot plate reflow ovens, infrared reflow ovens, hot air reflow ovens, infrared hot air reflow ovens, gas phase reflow ovens, etc. that heat the entire PCB; laser reflow ovens and focused infrared reflow ovens are used for local heating of PCBs., Hot air flow reflow oven, etc.

1) Reflow oven that heats the entire PCB

The hot plate reflow oven was used in the early days of SMT. Due to the low thermal efficiency of this type of reflow oven, the uneven heating of the PCB surface and the special sensitivity to the thickness of the PCB, it was quickly replaced by other reflow ovens. Infrared reflow ovens were popular in the 1980s. When infrared radiation radiates, dark-colored components absorb more heat than light-colored components, and infrared rays do not have the ability to penetrate. Components in shadow areas blocked by large components cannot easily reach the soldering temperature, resulting in a large temperature difference on the PCB, which is unfavorable for soldering. Therefore, it is basically Need not. The hot air reflow oven has been used since the mid-1980s and has continued to this day. In recent years, hot air reflow ovens have adopted various measures in airflow design, equipment structure, materials, software and hardware configuration, etc. Therefore, all hot air reflow ovens have become the first choice for today's SMT reflow ovens. Infrared hot air reflow oven means that the heating source has both hot air and infrared rays. Due to the high soldering temperature of lead-free soldering, the reflow zone is required to increase thermal efficiency, so infrared heaters are added at the entrance of the hot blast stove and the bottom of the reflow zone, which not only solves the problems of high soldering temperature and speeds up the heating rate, but also saves energy. Therefore, the infrared hot air stove also has a certain utilization rate in today's lead-free soldering. Gas phase reflow furnaces were used in the early 1970s, but due to the high cost of equipment and media, they were quickly replaced by other methods. However, the gas-phase reflow oven has the advantages of accurate temperature control, heating media with different boiling points to meet different soldering temperatures of various products, high heat conversion efficiency, rapid heating, oxygen-free environment, uniform temperature throughout the PCB, and good soldering quality. Therefore, with the development of lead-free, the gas-phase reflow furnace has once again attracted people's interest, and is used for high-reliability and difficult-to-heat surface mount boards.

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2) Reflow oven for local heating of PCB

The laser beam reflow oven utilizes the excellent directivity and high power characteristics of the laser beam. The laser beam is concentrated in a small area and within a short period of time through the optical system, so that the welded part forms a highly concentrated local heating zone. A kind of reflow oven. During the soldering process, the substrate and the component body are kept at a lower temperature, the soldering stress is low, and the components and the substrate will not be damaged. However, because the equipment is very expensive, it is only used for thermal components, precious substrates and fine pitch Local welding of components. Focused infrared reflow ovens are generally suitable for rework stations for rework or partial soldering. Hot air flow reflow furnace refers to a type of reflow furnace in which air or nitrogen is introduced into a special heating head and hot air flow is used for welding. This kind of reflow oven needs to process nozzles of different sizes for different sizes of solder joints, and the speed is relatively slow, so it is mainly used for rework or development.