2006 Volume 70 Issue 5 Pages 402-411
The effects of halogenation treatments on the bond strength of the solid-state diffusion-bonded joint of tin have been investigated mainly by TEM observations of the interfacial microstructure. The halogenation treatment was carried out by exposing a tin surface (finished by grinding on emery paper) to a vapor of hydrochloric acid or hydrofluoric acid in a closed container. The halogenation treatments both by hydrochloric acid and by hydrofluoric acid decreased bonding temperatures by ~30 K at which bonded joints could be obtained and bond strength comparable with the base metal was achieved. TEM observations of the joint interface revealed that massive particles a few μm in size were distributed at the interface, when the halogenation treatment by hydrochloric acid was applied. The particle was identified as an amorphous phase consisting of Sn, Cl, and O on the bases of SAD patterns and EDX analyses. When the halogenation treatment by hydrofluoric acid was given to the surface, rodlike particles consisting of Sn, F, and O were observed at the interface. The rodlike particle was composed of crystalline SnO particles and an amorphous SnFx matrix. These particles consisting of Sn, X (=Cl or F), and O were much coarser and lower in number densities than the Sn-oxide inclusion observed when the halogenation treatment was not applied. As the bonding temperature was increased, the Sn-X-O particle coarsened and decreased in number densities, leaving the surrounding area with much smaller amounts of inclusions distributing in the tin substrate than those of the Sn-oxide observed at the joint interface bonded without the halogenation treatment. The formation and enlargement of the areas with much smaller amounts of inclusions in the interfacial region probably contributed to the increase in the bond strength at lower bonding temperature by the halogenation treatments.
