The main process parameters of reflow soldering are heat transfer, chain speed control and wind speed control. Guangshengde will share with you in detail.

1. Control of heat transfer in reflow soldering

At present, many products use lead-free process, so the reflow welder is mainly hot air reflow soldering. In the process of lead-free welding, we need to pay attention to the heat transfer effect and heat exchange efficiency, especially for the components with large heat capacity, if the heat transfer and exchange can not be fully achieved, the heating rate will obviously lag behind the small heat capacity devices, resulting in the transverse temperature difference. The air transport mode of reflow furnace directly affects the heat exchange rate. The two hot air transfer modes of reflow soldering are microcirculation hot air transfer mode and small circulation hot air transfer mode.

The hot air of microcirculation is blown out from the hole of heating plate. The hot air flows in a small range, and the effect of heat transfer around is not good. The design of small circulation is due to the concentrated flow of hot air and clear direction. The results show that the heat transfer effect of hot air heating increases about 15%, and the increase of heat transfer effect will play a greater role in reducing the transverse temperature difference of large and small heat capacity devices.

2. Control of reflow chain speed

The control of reflow chain speed will affect the lateral temperature difference of PCB. Generally speaking, reducing the chain speed will give the device with large heat capacity more heating time, thus reducing the transverse temperature difference. But after all, the setting of furnace temperature curve depends on the requirements of solder paste, so it is unrealistic to reduce the chain speed without limit in actual production.

3. Control of air velocity and air volume in reflow soldering

Keep other conditions in reflow soldering furnace unchanged, and only reduce the fan speed in reflow soldering furnace by 30%, the temperature on the circuit board will drop about 10 degrees. It can be seen that the control of wind speed and air volume is very important for furnace temperature control.

In order to realize the control of wind speed and air volume, we need to pay attention to two points

a. The speed of fan should be controlled by frequency conversion to reduce the influence of voltage fluctuation;

b. Try to reduce the exhaust air volume of the equipment, because the central load of the exhaust air is often unstable, which is easy to affect the flow of hot air in the furnace.