Characterization of Soldering Alloy Type Bi-Ag-Ti and the Study of Ultrasonic Soldering of Silicon and Copper

The aim of the research work was to characterize the soldering alloy type Bi-Ag-Ti and to study the direct soldering of silicon and copper. Bi11Ag1.5Ti solder has a broad melting interval. Its scope depends mainly on the content of silver and titanium. The solder begins to melt at the temperature of 262.5 degrees C and full melting is completed at 405 degrees C. The solder microstructure consists of a bismuth matrix with local eutectics. The silver crystals and titanium phases as BiTi2 and Bi9Ti8 are segregated in the matrix. The average tensile strength of the solder varies around 42 MPa. The bond with silicon is formed due to interaction of active titanium with the silicon surface at the formation of a reaction layer, composed of a new product, TiSi2. In the boundary of the Cu/solder an interaction between the liquid bismuth solder and the copper substrate occurs, supported by the eutectic reaction. The mutual solubility between the liquid bismuth solder is very limited, on both the Bi and the Cu side. The average shear strength in the case of a combined joint of Si/Cu fabricated with Bi11Ag1.5Ti solder is 43 MPa.

Automated summary

The research focused on characterizing the Bi-Ag-Ti solder alloy and studying its direct soldering properties with silicon and copper. The study found that the solder has a broad melting interval and a microstructure consisting of a bismuth matrix with silver crystals and titanium phases segregated in the matrix. The interaction between the solder and silicon, as well as the copper substrate, was also investigated, with the average shear strength of joints using Bi11Ag1.5Ti solder reported to be 43 MPa.