Forced hot air convection is the best choice for SMT reflow soldering and lead-free reflow soldering. It has some different characteristics of infrared and other methods which are closely related to the physical properties. Due to the accelerated popularization and application of lead-free solders, the forced air convection welding process More aroused people's attention. Infrared radiation energy is transmitted directly, when a small, thin device close to large size, high device will shadow, resulting in uneven radiation. Mandatory hot air convection oven there are many obvious advantages.

Forced to increase the speed of hot air, accelerated heat transfer to the PCB chip mounted device speed. Excessive wind speed can cause the device to shift or break away from the original placement. Therefore, the speed of the hot air must be such that the device under the hot air nozzle opening will not cause displacement. Greater wind speeds are received around the PCB because the hot air flow at this location is a mixed air flow of both direct hot air flow and hot air flow transmitted from adjacent locations. In a fixed section of the PCB hot air flow increases, the hot air velocity will inevitably increase.

Due to the difference between reflow hot air flow and wind speed, the pressure on the PCB mounting surface is different. A high pressure zone is created in the center of the hot blast zone of each hot blast nozzle. That is, the farthest part from the center of the PCB is the highest pressure and the adjacent part is lower, which is caused by the hot air flow and the hot air velocity at a fixed PCB section.

Differences in hot air direction are inherent drawbacks in many convection oven designs. For example, use two identical devices, one on the PCB mounting surface and in the longitudinal center of the oven and the other on the edge of the PCB mounting surface. The front mounted device is directed at the hot air nozzle. The hot air flow angle is an orthogonal vector to the mounting surface of the PCB. However, components mounted on the edge of the PCB, in addition to being directly aligned with the hot air flow from the hot air nozzle, Neighboring hot air, the resulting hot air flow vector is less than the acute angle at right angles.

Because of the direction of the hot air flow in contact with their package, the heat rates obtained by the two identical device groups are different. This problem in the ball-pin device and printed circuit board at the bottom of the space between the distribution of hot air flow becomes more prominent. Such as BGA reflow soldering process, the bottom of the package pin and printed circuit board hot air flow less than the printed circuit board mounting surface of the pin device.

In the industry, there is no objection that forced air convection is the best choice for SMT reflow soldering. Many experts also agree that valuable improvements should be made to this technology, including system capabilities to increase the hot air temperature, speed, flow, uniformity and consistency of the PCB mounting surface in the oven.