What Is SMT Reflow Soldering? Core Process Principle
2026-04-30 14:40:57 - Source：PCB Assembly
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Reflow soldering is one of the most critical procedures in SMT production, and it directly determines the solder joint quality and reliability of PCBA products.
In short, solder paste is printed on PCB pads first, then components are placed by pick-and-place machine. The board is sent into the reflow oven and heated according to a professional temperature profile. The solder paste melts, wets the pads and component leads, then cools down and solidifies to form firm and conductive solder joints.
The reflow oven is divided into four key temperature zones:
Preheating Zone
Gradually raise temperature to evaporate solvent inside solder paste, avoid solder splashing and component thermal shock.
Soak Zone
Keep stable temperature to activate flux, remove surface oxidation of pads and pins, and improve solder wettability.
Reflow Zone
Reach the melting point of solder paste. Solder fully melts and forms reliable metallurgical connection between components and PCB pads.
Cooling Zone
Cool down steadily to make solder joints solidify with bright appearance and stable structure, avoiding cold solder joints and cracks.
The reflow temperature profile is the key to control soldering defects such as bridging, tombstoning, voids and solder beads.
Globalwell optimizes reflow parameters for different PCB and components, strictly controlling soldering quality and ensuring long-term reliability of PCBA products.
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