Vapor Reflow Soldering

What is vapor reflow soldering?

Vapour reflow refers to an advanced PCB soldering technology that uses an inert liquid with a high boiling point. In recent years, this technology has become popular among large PCB assemblers. To solder electronic components to the PCB, manufacturers usually require high temperatures. This is a complicated process, and as electronic components become smaller and smaller, it becomes more challenging. Vapor reflow soldering ensures that the PCB board and its components will not be exposed to temperatures higher than necessary. Therefore, the parts will not overheat. This welding process provides ideal detail wetting. In addition, the entire welding process is performed in an inert atmosphere. Finally, PCB assemblers obtain the highest possible PCB soldering results.

Convection reflow furnace

Convection reflow furnace usually occupies a large area, so it occupies a large area in the factory. Although each heating zone has its own temperature control, engineers often face challenges when refluxing dense circuit boards in a convection reflow furnace, because it is impossible to control the temperature at a single element level.

The production line of the printed circuit board is usually placed in the convection reflux between the line and the SMT assembly equipment furnace, thus allowing relatively high throughput without additional processing. However, each product needs its own backflow curve, which the engineering team must create before starting production.

Gas-phase reflow soldering

Unlike convection, this type of oven uses condensation or vapor phase welding. The steam comes from boiling perfluoropolyether, an inert heat transfer liquid. Compared with the convection reflow soldering furnace, the gas phase reflow soldering furnace occupies a much smaller area, and the PCB assembly moves vertically up and down rather than laterally.

When the component is located in it, the steam layer transfers heat to the PCB and related components. High heat transfer rate, good wettability, much less power input required. This process produces a small temperature difference between components with different thermal qualities on PCB. This makes the process very suitable for densely populated PCB.

In the gas phase furnace, the limitation of physical temperature can reliably prevent the overheating of any parts in the welding process. Because steam has a higher density, it is heavier than the surrounding air. This allows the welded parts to remain sealed in a neutral atmosphere. For example, an inert fluid boils at 230 ° C and forms a vapor layer above it at 230 ° C. However, the air above the gas phase will not heat more than 50-80 ° C.

The heat transfer fluids used in modern gas-phase reflux furnaces, such as perfluoropolyether, do not contain any CFCs or other harmful components that may restrict the transportation and storage of these fluids. Its main performance is excellent chemical resistance and heat resistance, high electrical insulation performance, non-toxic, low viscosity, no flash point or ignition point.

Composition of vapor phase reflux

Vpr process relies on three different layers, which provide ideal conditions for top-level welding. These three layers are basic fluid layer, steam layer, and preheating zone.

In the basic fluid layer are the chemicals you heat to provide the necessary steam for welding. In order to obtain satisfactory results, it is best to choose the liquid with appropriate quality. We have outlined some of these features.

The actual welding process of steam layer treatment. The advantage of the steam layer is that there is no temperature fluctuation. This means you don't have to worry about overheating components.

Preheating layer helps to avoid welding defects. When you hover the PCB directly over the vapor layer, actual preheating occurs. Keep in mind that there are many preheating techniques depending on the machine you are using.

Characteristics of vapor phase soldering

Vapor Reflow Soldering Advantage:

• Higher heat transfer rate: the vapor phase reflow process requires a lower temperature to ensure the ideal solder. Most reflow methods require additional heat up to 35 ° C to achieve a perfect weld. However, Vpr only needs 5 to 10 ° C higher than the melting point of solder paste to complete the same task. This is because the heat transfer rate of VPR process is higher.
• Good wettability: the gas phase reflux process also provides a completely oxygen-free atmosphere. So you can get excellent wettability at no extra cost. The energy consumption is much lower than that of the convection furnace reflux process. With the insulation in Vpr, very little heat is released to the surrounding environment, which means you don't need additional air conditioning.
• Environmental protection: gas-phase reflux process is also one of the cleanest and safest processes. Initially, many older reflow welders used freon, which may be unstable. Current Vpr machines do not require VOCs to run. Fluorinated fluid is inert, non-toxic, non-corrosive, non-combustible, and nonpolluting. The liquid usually evaporates completely from the plate, leaving no residue. It makes Vpr one of the most environmentally friendly reflux processes.
• Uniform heating: another significant advantage of this technology is uniform heating. The size, shape, color, or geometry of PCB components will not affect the vapor phase reflow process. Vpr exposes each part of each element to exactly the same temperature. It makes the gas phase reflow process very suitable for reflow multilayer board and a large board. Vpr is also very suitable for panels with various size components and densely populated circuit boards.
• Temperature control: one of the biggest benefits of using gas-phase reflux technology is that it provides excellent temperature control. At atmospheric pressure, the temperature of the vapor is the same as that of the boiling liquid. This means that the temperature fluctuation is minimal. It is different from other reflux processes, such as convection furnaces and infrared heating. If you raise the temperature, the rate of steam generation will increase, but the weather won't change.
• Space-saving: the gas oven is also more compact than a convection oven. If saving space is one of your concerns, this is a considerable advantage.

Disadvantages of gas-phase reflux

The main disadvantage of the gas phase reflux process is that it requires more manual operation than some other alternatives. Therefore, the VPR process is more suitable for mass production, which will affect the potential throughput. There are gas-phase systems that cater for mass production, but they tend to cost more than most convection ovens. Another disadvantage of gas-phase reflux technology is that it is more time-consuming than other solutions.