Temperature profiles are very important in mass production PCBA processing and soldering environments. During smt placement, a slow ramp-up and preheat phase helps activate flux, avoid thermal shock and improve solder quality. However, when it comes to rework, prototyping, or PCBA proofing projects, it's easy to forget the importance of the warm-up phase, which can result in equipment that can be severely affected if not damaged. So, for such an important step, why is it often forgotten in the actual operation of smt processing plants? What are the consequences of ignoring this step?

  1. What is preheating before PCBA soldering?

  When technicians and practitioners hear the word "temperature profile", smt reflow soldering comes to mind. Along the expansive welding area, it is easy to see 4 main temperature controlled areas, resulting in a perfect welded joint. At each stage, technicians rely on their own experience, trial and error, strict control and improvement, and each stage can improve the quality of solder joints and reduce defects. But other industrial soldering equipment may not have such precise temperature control, but they all have a common preheat stage.

  2. Flux burning in selective wave soldering

  The role of the preheat stage is to bring the temperature of the entire assembly up steadily from room temperature to a holding temperature below the melting point of the solder paste, about 150°C. Adjust the temperature change so that the slope remains at a few degrees per second. A period of time after the preheating stage is the soaking period, during which the temperature is maintained for a period of time to ensure that the plate is heated evenly. Then it enters the reflow stage, where solder joint formation begins. During the preheating and soaking process, the volatile solvent in the solder paste is burned off and the flux is activated.

  Recast's production practice has proved that preheating before PCBA processing is very important.