Transient-liquid-phase (TLP) joining and liquid-film-assisted joining (LFAJ) exploit thin
metallic films that melt at relatively low temperatures as part of a multilayer, multimaterial
interlayer to enable joining at reduced temperatures. These methods are attractive for assemblies
that include temperature-sensitive components, however, unlike conventional low-temperature
joining methods, they also offer the potential for service at temperatures approaching or even
exceeding the original joining temperature. In successful TLP joining and LFAJ, the wetting
behavior of the liquid plays a critical role. In TLP joining, the liquid ultimately disappears during
joining due to interdiffusion and chemical homogenization. In contrast, in LFAJ the liquid persists
at the joining temperature, provides a high-diffusivity transport path that accelerates joint
formation, and ultimately undergoes a morphological transition that disrupts the initially continuous
film. The resulting isolated liquid droplets solidify on cooling. Current studies of these joining
methods are described, and promising future directions are indicated.