Low Temperature Active Bonding Mechanism of Sn3.5Ag4Ti (Ce,Ga) Alloy Filler with SiC Substrates

In this work, the soldering of Sn3.5Ag4Ti (Ce,Ga) active alloy filler with SiC substrates in different times was conducted to explore the soldering mechanisms at 250 °C in air. Experiment results showed that the microstructure and element distribution are closely related to the soldering time. A series of experiments were carried out at 250 °C, and the soldering times were set to be 1, 15, 30, 60 min, respectively. Cross-section of the solder joints were observed by a scanning electron microscopy (SEM) and the element distribution were analyzed by energy dispersive spectrometer (EDS). Results show that when the soldering time is 60 minutes, the Ti element is segregated at the SiC/SnAgTi interface. By theoretically analyzing the wetting behavior of the active solder at the SiC substrate, it could be inferred that the adsorption of the active element titanium at the SiC/solder interface plays a key role, which reduces the interface energy and drives the molten solder well wetting on the surface of SiC substrates at low temperature. The interfacial behavior of Ti between active solder and SiC substrate has been studied and bonding mechanism has been explored. Our understanding of the wettability of alloy solder on SiC, the diffusion kinetics of Ti element, and soldering mechanism provides the basic knowledge for the development of low temperature active soldering technology.