Microstructural Evolution of Ni-Sn Transient Liquid Phase Sintering Bond during High-Temperature Aging

Abstract

For high-temperature-resistant packaging of new generation power chip, a chip packaging simulation structure of Ni/Ni-Sn/Ni was bonded by a transient liquid-phase sintering process. High-temperature aging experiments were carried out to investigate joint heat stability. The microstructural evolution and mechanism during aging, and mechanical properties after aging were analyzed. The results show that the 30Ni-70Sn bonding layer as-bonded at 340°C for 240 min is mainly composed of Ni₃Sn₄ and residual Ni particles. When aged at 350°C, because of the difficulty of nucleation for Ni₃Sn and quite slow growth of Ni₃Sn₂, the bonding layer is stable and the strength of that doesn’t change obviously with aging time. When aging temperature increased to 500°C, however, the residual Ni particles were gradually dissolved and the bonding layer formed a stable structure with dominated Ni₃Sn₂ after 36 h. Meanwhile, due to the volume shrinkage (4.43%) from Ni₃Sn₂ formation, a number of voids were formed. The shear strength shows an increase, resulting from Ni₃Sn₂ formation, but then it decreases slightly caused by voids. After aging at 500°C for 100 h, shear strength is still maintained at 29.6 MPa. In addition, the mechanism of void formation was analyzed and microstructural evolution model was also established.