In reflow soldering, lead-free reflow soldering, forced air convection oven compared with the infrared furnace, has the obvious advantage of reducing the heating temperature difference of the plane of the printed circuit board. Even the convection oven, the natural cooling furnace wall, the center of the furnace temperature is higher than the surrounding furnace wall. As a result, the process engineer had to consider having enough heat to reflow the edge-mounted components of the PCB when setting the reflow process parameters, resulting in damage or overheating of the temperature-sensitive components near the center.

Convection reflow oven usually use a group of heaters on the top of the PCB hot air heating, the other heater on the bottom of the PCB hot air heating. Any temperature difference between the two sides of the board will introduce stress to the material, resulting in bending deformation or delamination.

Conventional reflow oven Furnace Road, the hot air flow in contact with the printed circuit board continue to move to the furnace wall furnace direction. The cooled hot air stream is collected by a pressure tank and reheated, which is then repeatedly applied to the printed board. This blowing to the central part of the PCB hot air flow was significantly lower than any point around the PCB. Because the printed circuit board not only received direct hot air flow around, but also to be cooled by the hot air flow through the PCB peripheral parts were eventually collected by the pressure tank.

Convection oven furnace / hot air return flow collection system, the hot air flow and printed circuit board contact continue to flow to the furnace wall was cooled collection, reheating return to the furnace, this phenomenon led to a variety of inconsistencies:

1, PCB peripheral exposure to high hot air flow but low temperature environment, so to further expand the PCB central high temperature hot zone and the surrounding low temperature cold zone temperature difference.

2, Most reflow furnaces use a system called nozzle to deliver hot air flow. However, the flow of hot air directly between the two nozzle openings and the area immediately below each nozzle opening is significantly different.

3, hot air flow at a certain point in the PCB surface is different from another vertical point, making the rate of volatilization of the organic solvents in the solder paste is different, resulting in differences in flux component activity and dehydration conditions.