What are the factors affecting reflow soldering technology

Reflow welder, also known as reflow welder or "reflow oven", is a machine that provides a heating condition to heat and melt the solder paste so that the surface mounted components and PCB pads can be firmly integrated with solder paste alloy.

Process factors:

In surface mount technology, the factors causing uneven heating of components by reflow soldering process mainly include: the difference between the heat capacity and absorbed heat of reflow soldering components, the edge effect of conveyor belt or heater, and the load of reflow soldering parts.

1. generally, PLCC and QFP have larger heat capacity than a discrete sheet element, and it is more difficult to weld large-area components than small components.

2. in the reflow soldering furnace, the transfer belt makes the transfer weldment reflow again and again. At the same time, it also forms a heat dissipation system. In addition, there are differences in the heat dissipation environment between the edge and the center of the heating part. The edge temperature is usually low. In addition to the different temperature requirements in each temperature zone, the temperature of the same carrier surface is also different.

3. influence of weldment loading difference. The setting of temperature curve of reflow soldering should consider the good repeatability under no-load, load and different load factors. Load factor is defined as: lf=l/ (l+s); Where l= length of assembled base plate, s= interval of assembled base plate.

The larger the load factor, the more difficult the reflow soldering technology is to achieve good repeatability. Generally, the maximum load factor of reflow soldering furnace ranges from 0.5 to 0.9. This shall be determined according to the weldment conditions (element welding density, different substrates) and the different models of the reflow furnace. In order to obtain good welding results and repeatability, practical experience is very important.

Reflow soldering is a welding technology developed with the emergence of miniaturized electronic products. It is mainly used for the welding of components assembled at various levels. The solder of this welding technology is solder paste. Apply appropriate and appropriate solder paste on the solder pad of the circuit board in advance, and then paste the SMT components at the corresponding positions; The solder paste has a certain viscosity to fix the components; After that, the circuit board with the components installed will enter the reflow soldering machine. The transmission system drives the circuit board to pass through the temperature areas set in the machine. The solder paste connects the components to the printed board through drying, preheating, melting, wetting and cooling. The core step of reflow soldering is to use an external heat source to heat, so that the solder melts and flows and soaks again to carry out the soldering process of the circuit board.