Pressureless transient liquid phase sintering bonding in air using Ni and Sn-58Bi for high-temperature packaging applications

摘要

High heat-endurance bonding has become an important technology requisite for the demands of SiC die attachment or other high-temperature packaging applications. Transient liquid phase sintering (TLPS), which is a promising candidate among high heat-endurance bonding technologies, has been widely studied in recent years. Because the advantages of TLPS bonding are short bonding time, low bonding pressure, and low cost. In this study, in order to bond in air condition and low temperature, TLPS pastes using Ni, Sn-58Bi, and flux were fabricated with various weight ratios. Pressureless TLPS bonding processes were conducted in an oven at 220 ℃ for 60 min in air. The thermal behaviors of TLPS pastes (before bonding) and TLPS joints (after bonding) were analyzed by differential scanning calorimetry (DSC). The shear test was conducted for investigate about mechanical properties. The microstructures of cross-sectional and fracture surfaces were analyzed by field emission scanning electron microscopy (FESEM). Also, the atomic distribution of cross-sectional micrographs was analyzed by electron probe micron analyzer (EPMA) and electron dispersive spectrometry (EDS). After bonding, the residual eutectic Sn-Bi lamellar structure was observed only in Ni-90(Sn-58Bi). To verify the reliability of TLPS joints, the samples were stored in an oven at 200 ℃ for 100, 500, and 1000 h, and the shear test was conducted. The initial shear strengths of Ni-90(Sn-58Bi), Ni-80(Sn-58Bi), and Ni-70(Sn-58Bi) TLPS joints were 23.56, 17.23, and 5.47 MPa, respectively. After the high-temperature storage test, the decrease in shear strength was smallest in Ni-70(Sn-58Bi) and largest in Ni-90(Sn-58Bi). In conclusion, the optimum weight ratio of Ni and Sn-58Bi was Ni-80(Sn-58Bi) because of increased re-melting temperature (270 ℃) and high bonding reliability compared to other conditions.