Now more and more electronic components are converted from through-hole to surface mount, and it is an obvious trend in the soldering industry that the reflow soldering process replaces the wave soldering process in a considerable range.
So How the reflow oven works?
When the PCB enters the heating zone (drying zone), the solvent and gas in the solder paste evaporate, and at the same time, the flux in the solder paste wets the pad, component terminals and pins, and the solder paste softens, collapses, and covers 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 welding high temperature area and damaging the PCB and components → when the PCB enters the welding In the zone, the temperature rises rapidly to make the solder paste reach a melting state, and the liquid solder wets, diffuses, diffuses or reflows the PCB pads, component terminals and pins to form solder joints → PCB enters the cooling zone to solidify the solder joints . At this point the reflow is complete.
During the reflow soldering process, the paste solder paste composed of tin-lead solder, adhesive and flux can be applied to the printed board manually, semi-automatically or fully automatically, and a manual, semi-automatic or automatic screen printing machine can be used , to print the solder paste onto the printed board like a mimeograph. Then use a manual or SMT pick and place machine to mount the components to the printed board. Use the heating furnace in reflow soldering or the method of hot air to heat the solder paste to reflow. , This process includes: preheating zone, constant temperature zone, reflow soldering 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 able to achieve good soldering of various surface mount components on the PCB board to be soldered, and the solder joints not only have good appearance quality but also have a good internal quality temperature curve.
