The Working Principle of Reflow Soldering

Reflow soldering is a technology that achieves reliable bonding between electronic components and circuit boards by precisely controlling changes in hot air temperature, causing the solder paste pre-applied to the PCB pads to undergo a melting and solidification process. Its working principle and process are as follows:

1. Core Working Principle

‌Hot Air Circulation Heating‌

A fan inside the equipment drives gas (air or nitrogen) through heating elements to form high-temperature airflow, which circulates within a sealed furnace chamber to uniformly transfer heat to the PCB board and components.

Nitrogen protection reduces oxidation, improving solder joint wettability and reliability.

Solder Paste State Change

During the heating process, the solder paste undergoes a physical reaction: solid tin powder particles melt into a liquid state, wetting the component leads and pads, and then solidify again upon cooling to form solder joints.

2. Key Technical Features

Heat Transfer Method

The mainstream method uses forced convection hot air, which provides more uniform temperature distribution and reduces shadow effects compared to early infrared heating.

Gas Control

A nitrogen (N₂) environment reduces solder joint porosity and improves soldering quality.

Temperature Zone Design

Multiple independent temperature zones (typically 8–10 zones) precisely match different solder paste temperature curves.

‌Naming Origin‌: Since gas circulates within the furnace (reflow) to achieve soldering, it is called ‘reflow soldering’‌.

This process is widely used in the SMT assembly field, offering advantages such as temperature control, minimal oxidation, and suitability for high-density soldering‌.