Soldering terminology

Reflow soldering of PCBs with solder paste is usually carried out in a far-infrared reflow oven. Due to the different light absorption of colors and the fact that components lying in shadow have no access to direct heating, it is difficult to achieve uniform solder coverage. In contrast, hot air provides comprehensive heating of the PCB, regardless of the shape and color of the components. The disadvantage of the method is that the speed of the air flow has a major influence and must be regulated accordingly. The same applies to the low heat transfer coefficient, which makes rapid heating impossible. Because the solder paste has a poor adherence at low temperatures, smaller components such as chips may be dislodged by a strong airflow in the preheating phase. Since both methods have their advantages and disadvantages, a combination of the two is preferable where infrared light is used during preheating and hot air of a uniformly high temperature during the reflow process.