What is reflow soldering? What kinds are there?

Date：2022-06-06 15:29:41Views：1387

The quality of welding directly determines the quality of the whole product, and the welding quality depends on the welding materials, welding equipment and welding technology. Soft soldering technology is adopted in the SMT process, mainly including reflow soldering and wave soldering. In order to help you understand deeply, this article will summarize the relevant knowledge of reflow soldering. If you are interested in what this article will cover, read on.

1、 What is reflow soldering?

Reflow soldering relies on the effect of hot air flow on the solder joint to make the physical reaction of the gel solder paste under a certain high-temperature air flow to achieve smc/smd welding. Because the gas circulates in the welder to produce high temperature to achieve the purpose of welding, it is called reflow soldering.

2、 Classification by technology

1. Hot air reflow soldering

By using the heater and fan to heat, the internal temperature can be continuously increased and then circulated. This kind of reflow welding is characterized by transferring the heat required during welding through the laminar flow of hot air; The advantage is that the heat energy is always kept within a certain temperature range during welding, and there will be no sudden heat or cold, so the welding is easier and the success rate is higher.

2. Hot gas reflow welding

Hot gas reflow welding is characterized by using hot gas for welding. This welding method needs to constantly adjust the welded joints according to the size of welding, which greatly reduces the welding efficiency.

3. Hot wire reflow soldering

Direct welding with heated metal is often used on cables. Its joints have certain flexibility. Therefore, the method of heating without solder paste can be used for welding. Because it is a relatively difficult welding technology, the welding speed is slow, which slows down the work efficiency.

4. Induction reflow soldering

Using a principle of inductive eddy current, this product does not need to contact machinery, which reduces a carrier and greatly improves the heating speed. However, it is difficult to control the temperature because of the lack of carrier, and it is easy to make mistakes if the technology is not perfect.

5. Laser reflow soldering

The laser heating reflow welding is used for welding. Because the laser has good directivity and specificity, the laser welding can be used to process a point that needs to be welded, so that the welding products can be well controlled to reduce deviation.

6. Infrared (IR) reflow soldering furnace

Most of these reflow soldering furnaces are conveyor belt type, but the conveyor belt only supports and transports the base plate. Its heating method is mainly based on the infrared heat source. The temperature in the furnace is more uniform than the previous method, and the mesh is larger, which is suitable for reflow soldering and heating the base plate assembled on both sides. This kind of reflow soldering furnace can be said to be the basic type of reflow soldering furnace. Many are used in China, and the price is relatively cheap.

7. Vapor phase reflow welding

Vapor phase reflow soldering is also called vapor phase soldering (VPS), also known as condensationsoldering. Heat the carbon fluoride (fc-70 fluorochloroalkane solvent was used in the early stage), the melting point is about 215 ℃, and the boiling produces saturated steam. There are condensing tubes above and around the furnace to limit the steam in the furnace. When encountering PCB components to be welded with low temperature, it will release the latent heat of vaporization, so that the solder paste can be melted and the components and pads can be welded. It was first used in the welding of thick film integrated circuits (ICS) in the United States. The release of the latent heat of the gas cypress is not sensitive to the physical structure and geometry of SMA. It can make the components uniformly heated to the welding temperature, and the welding temperature is kept at a certain level. There is no need to use temperature control means to meet the needs of welding at different temperatures. The gas phase of VPS is saturated steam, with low oxygen content and high thermal conversion, but the solvent cost is high, and it is a typical ozone layer depleting substance, Therefore, the application is greatly limited, and the international community no longer uses this environmentally damaging method.

3、 Classification by shape

1. Bench type reflow soldering furnace

Desktop equipment is suitable for PCB assembly and production in small and medium batches, with stable performance and economic price. It is widely used by domestic private enterprises and some state-owned units.

2. Vertical reflow furnace

There are many types of vertical equipment, which are suitable for PCB assembly and production of users with different needs. The equipment is available in high, middle and low grades, with different performance and prices. It is widely used by domestic research institutes, foreign enterprises and well-known enterprises.

3、 Classification according to temperature zone

The length of temperature zone of reflow soldering furnace is generally 45cm ~ 50cm, and the number of temperature zones can be 3, 4, 5, 6, 7, 8, 9, 10, 12, 15 or more. From the perspective of welding, reflow soldering has at least 3 temperature zones, namely preheating zone, welding zone and cooling zone. Many furnaces usually exclude the cooling zone when calculating the temperature zone, that is, only the heating zone, insulation zone and welding zone are calculated.

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