reflow

The term reflow is used both for the soldering process in the surface mounting of printed circuit boards, but also for the cleaning of wafers.

1. Reflow is an assembly process in the manufacture of printed circuit boards. The reflow process is used to solder electronic components onto the solder pads of the printed circuit board. In the reflow process, the solder paste present at the soldering points - a mixture of solder and flux - is liquefied and bonded to the component connections by brief controlled exposure to heat from infrared light, gas, hot air or from a laser. During cooling, the solder joint hardens. Special reflow soldering systems, infrared lamps and heated air nozzles are available for this purpose. The reflow technique is particularly suitable for surface-mount SMT technology, but it can also be used in through-hole technology, where the holes for the component connections are filled with solder paste. During reflow, it is critical that the electronic components are not overheated and damaged as a result. Wave soldering or wave soldering is available as an alternative to the reflow process.
2. To make the wafer surface completely flat and edge-free during chip manufacture, the wafer is coated with an extremely thin glass layer of phosphorus silicate. This process is called reflow. The glass layer has a low melting point and flows evenly over the wafer surface at temperatures of about 900 °C. The glass layer is then applied to the surface of the wafer. Since the melting point of various metals is below this temperature, the reflow process cannot be used to produce metallization layers.