Ni–Sn SLID bonds for assembly at extremely high temperatures

Ni–Sn solid-liquid interdiffusion bonding (SLID) has shown potential for assembly of materials in high-temperature applications up to $600^{\circ}\mathrm{C}$. This paper attempts to fabricate a bond with a specific intermetallic phase of Ni$_{3} Sn_{2}$ to push the temperature stability to $1000^{\circ}\mathrm{C}$. Experiments were conducted using Si/TiW(10:90)/Ni/Sn dies where a two-step bonding process was used. The first step was bonding at $285^{\circ}\mathrm{C}$ for 5 hours. The bonded dies showed fractures perpendicular to the bonding plane indicating significant thermomechanical tensile forces. The initial voiding was 5% less than theoretically expected. The second step was annealing at $600^{\circ}\mathrm{C}$ for 1 hour and 3 hours, resulting in the final bonds with a layered structure of $Ni/Ni_{3} Sn/Ni_{3} Sn_{2} /Ni_{3} Sn_{4} /Ni_{3} Sn_{2} /Ni_{3}$ Sn/Ni. The bonds after 3 hours annealing had no remaining Ni. New fractures along the bonding plane appeared propagating through the remaining Ni$_{3} Sn_{4}$ indicating large thermomechanical shearing forces. Voiding increased by a further 6% after the 1 hour anneal. For the bonds with 1 hour anneal, the new voids were seen at the Ni$_{3} Sn_{4}$ /Ni$_{3} Sn_{2}$ interface and at the Ni
3
Sn/Ni interface. The growth constant for Ni$_{3} Sn_{2}$ at $600^{\circ}\mathrm{C}$ was 3.5$\mu m/min^{n}$, while the growth exponent was 0.2 giving a homogenization time of $\sim 60$ hours for the experimental bondline thickness of 38$\mu$m. Thus, larger annealing temperatures or times are needed to accelerate bonding.