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Reflow soldering, also known as reflow soldering, is developed with the appearance of miniaturized electronic products. It is mainly used in the soldering technology of all kinds of electronic surface assembly components. The solder for reflow soldering is solder paste. Before soldering, apply a proper amount and proper form of solder paste on the pads of the circuit board in advance, and then place the surface mount components on the corresponding pads through the placement machine. The solder paste has a certain viscosity, so that the mounted components are fixed on the pad. Then, the circuit board with the mounted components is transported to the reflow oven through the conveyor belt. The circuit board is preheated, insulated, reflowed, and cooled in the reflow oven. The solder paste is dried, preheated, melted, wetted, and cooled to solder the components to the printed circuit board. The original intention of reflow soldering is to form solder joints by remelting the pre-placed solder. It is a soldering method that does not add any solder during the soldering process. Reflow soldering can be used to solder various high-precision, high-demand components, such as 0603 resistors, 0603 capacitors, and chip packaging devices such as BGA, QFP, and CSP.
There are many types of reflow soldering. According to the different heating areas of the components, reflow soldering is usually divided into two categories: overall reflow soldering and partial reflow soldering. According to different heating methods, reflow soldering is usually divided into three categories: infrared hot air reflow soldering, vapor reflow soldering and laser reflow soldering.
Nowadays, the reflow soldering technology of through-hole components has matured. With the full implementation of lead-free soldering technology, the price of solder has increased, and the advantage of low-cost wave soldering has been gradually lost, which will make more and more electronic products Use reflow soldering process.
Two, SMT wave soldering
Wave soldering is also called group soldering and flow soldering. Wave soldering originated in the 1950s. Mainly used in through-hole inserting process, surface assembly and through-hole inserting mixed assembly process. Surface mount components such as rectangular chip components, cylindrical chip components, SOT, smaller SOP, etc. are suitable for wave soldering technology. The working principle of wave soldering is: the molten liquid solder forms a solder wave with a specific shape on the liquid surface of the solder tank under the action of a pump, and the printed circuit board with inserted components is transmitted through the transmission chain through the solder Wave crest, to realize the soldering of solder joints. The wave soldering process includes five steps: plate advancement, flux coating, preheating, soldering, and cooling.
Although the reflow soldering technology has many advantages compared with the wave soldering technology, the wave soldering technology is still indispensable in the mixed assembly process of SMT at present and even in the future for a long time. Wave soldering technology can greatly improve productivity, save manpower and solder to a large extent, and significantly improve the quality and reliability of solder joints. Therefore, wave soldering technology still has strong vitality at the moment.
Because the volume of electronic components is getting smaller and smaller, the density of PCB assembly is increasing, and the use of lead-free solder paste is becoming more and more frequent, so the wave soldering process is becoming more and more difficult.
