Soldering principle of reflow soldering: when the PCB enters the heating zone (dry zone), the solvent and gas in the solder paste evaporate, and at the same time, the flux in the solder paste wets the pads, component terminals and pins, and the solder paste Softening, slumping, covering the pads, component ends and pins are isolated from oxygen → when the PCB enters the heat preservation area, the PCB and components are fully preheated to prevent the PCB from suddenly entering the high temperature area of welding and damaging the PCB and components. Device → When the PCB enters the soldering area, the temperature rises rapidly to make the solder paste melt, and the liquid solder wets, diffuses, diffuses, or reflows the pads, component ends and pins of the PCB to form solder joints → The PCB enters cooling area to solidify the solder joint. Reflow soldering is now complete.
During the reflow soldering process, manual, semi-automatic, or fully automatic application of paste solder paste consisting of tin-lead solder, adhesive, and flux to the printed board can be used, and manual, semi-automatic or automatic screen printing machines can be used. , to print the solder paste onto the printed board like a mimeograph. Then use a manual or smt placement machine to bond the components to the printed board. The solder paste is heated to reflow using a furnace or hot air blower in reflow soldering. , this process includes: preheating zone, constant temperature zone, reflow zone and cooling zone.
Reflow soldering temperature profile:
To get a good reflow soldering effect, there must be a good reflow temperature profile (Profile). So what is a good reflow profile? A good reflow profile should be a temperature profile that can achieve good soldering of various surface mount components on the PCB to be soldered, and that the solder joints have not only good appearance quality but also good intrinsic quality.
The main welding process of reflow soldering can be divided into two types: single-sided and double-sided:
First: Let's talk about single-sided soldering of reflow soldering: first, apply solder paste, and pay attention to evenness when applying. If the application is uneven, the degree of heat during soldering will also be different. After smearing, start to install the patch. This is our theme for reflow soldering. Before starting, check the circuit status. If conditions permit, it is best to test it first;
Second: Double-sided mounting: First apply solder paste on one side, and then install the patch after it is evenly spread, and then perform reflow soldering. When one side is finished, start to repeat the work on the previous side.
