Soldering defect: wet defect (solder paste)

Introducing the wet defect of solder paste.

Issues with Poor Wetting When solder wetting is poor, the bonding area decreases, leading to reduced joint reliability. Causes of poor wetting include issues with the reflow profile and degradation of components and substrates. Concept of the Reflow Profile A method called the "trapezoidal profile" is employed, which involves a long preheating and main heating process. While the heat resistance temperature of components is around 250°C, the melting point of solder is approximately 220°C. By extending the preheating zone, temperature differences due to the size of components are eliminated, preventing wetting failures due to insufficient heat in large components and failures due to overheating in small components. Degradation of Solder Paste During Preheating The typical preheating temperature is between 150°C and 180°C, with a preheating time of 90 to 120 seconds. During preheating, the flux in the solder paste begins to react due to heat, gradually losing its activity and reducing wettability. Therefore, it is ideal to conduct preheating at the lowest possible temperature and for the shortest time, within a range where the component temperature rises to about 240°C during main heating. Wetting Measures with Solder Materials The flux in solder paste contains activators tailored to the preheating and main heating temperatures. Our company offers pastes that demonstrate good wettability across a wide range of preheating temperatures and various components.

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