What is preheating before PCBA soldering?

PCBA preheating: What is preheating before PCBA soldering?

Abstract: The importance of temperature profiling in the mass-production PCBA processing soldering environment is widely understood. Slow heating and preheating stages help to activate flux, prevent thermal shock, and improve solder joint quality during smt placement. However, when it comes to rework, prototyping, or PCBA first article projects, it is easy to forget the importance of the warm-up phase, which can lead to compromised, if not damaged, devices. So, for such an important step, why is it often forgotten when it is operated in the smt processing plant? What are the consequences of omitting this stage?

What is preheating before PCBA soldering?

When technicians and practitioners hear the words temperature profiling or temperature profiling, SMT reflow soldering comes to mind. The 4 main temperature control zones are easily visible along the huge length of the solder zone, which will eventually result in a perfect solder joint, hopefully. Each stage is carefully controlled and improved through technicians’ experience and trial and error, and each stage plays a role in promoting solder joint quality and reducing defects. But other industrial soldering machines may not have such fine temperature control. But what they all have in common is the warm-up phase.

Flux Burning in Selective Wave Soldering

The role of the preheat phase is to steadily increase the temperature of the entire assembly from room temperature to a soak temperature below the melting point of the solder paste, approximately 150°C. Adjust the temperature change to maintain a constant ramp of a few degrees per second. The preheat phase is followed directly by a soak phase, which holds that temperature for some time to ensure that the board is evenly heated. Then comes the reflow phase, which initiates solder joint formation. During the preheat and soak phase, the volatile solvents in the solder paste are burned off and the flux is activated.

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