**Table 1.**

*Active solders developed by Hillen et al. [4].*

their melting points, their lower solidification temperature can alleviate the thermal stresses in the ceramic-metal joint. Active soldering techniques, which provide for bonding of various ceramics and difficult-to-wet materials at low temperature, have also been developed [4]. The solders used for active soldering consist of a low melting point metal such as tin or zinc with active elements such as titanium and rare earth elements. There have been reports of active solders developed by adding rare earth elements (Ce, La) and a wetting promoter (Ga) into Sn–Ag–Ti, Zn–Ag–Ti, Sn–Bi–Ti, and In–Sn–Ti alloys [4, 24]. Hillen et al. initially developed active solders for soldering difficult-to-wet materials, as listed in **Table 1**. With these active solders, the joining process of ceramics can be performed at temperatures lower than 450°C without flux and without the need for premetallization or a protective atmosphere.
