Mechanism of Intermetallic Phase Formation in thin Liquidsolid Diffusion Couples

Abstract

ABSTRACTThin interconnection layers entirely consisting of intermetallic phases have been produced by joining planar Cu substrates coated with thin films of Sn. The thin layers of intermetallic phases are produced at low temperatures (<300°C) and short reaction times (5-120 s) in a process similar to reflow soldering by a liquid-solid reaction between Sn and Cu. Metallographic methods and X-ray analysis have been used to characterize the initial stages of the formation of the intermetallic phases. The reaction to form intermetallic phases via Cu dissolution and diffusion in the liquid Sn is very fast in the first 10-15 s when the liquid Sn is in contact with the Cu substrate along channels of liquid Sn between grains of the intermetallic phases. The stability of these narrow channels of liquid Sn is discussed in terms of the wettability of different types of grain boundaries in the textured layer of intermetallic phases.