<p>Cu/Sn-9Zn-10Ni/Ni 3D packaging solder joints were fabricated using Transient Liquid Phase (TLP) bonding. The effect of bonding temperature on the microstructure, shear strength, and fracture surfaces of the solder joints were investigated. The results showed that the thickness of the interfacial intermetallic compound (IMC) layer increased with increasing bonding temperature, and the activation energies for the growth of the Cu-side interfacial IMC and Ni-side interfacial IMC are 40.68&#xa0;kJ/mol and 41.53&#xa0;kJ/mol, respectively. As the bonding temperature increased, the (Cu, Ni)₆Sn₅ phase gradually transformed into Cu₃Sn in the Cu-side interfacial reaction zone, while the Ni-side interfacial reaction zone consisted entirely of Ni₃Sn₄. As the bonding temperature increased, the content of Ni₃Sn₄ phase and Zn-rich phase gradually decreased in the in situ reaction zone, while the content of Ni₃(Sn, Zn)₄ phase gradually increased, leading to the in situ microstructure coarsen. The shear strength of the solder joints first increased and then decreased with increasing bonding temperature, and the maximum shear strength reached 14.31&#xa0;MPa bonding at 270&#xa0;°C. As bonding temperature increased, the fracture location of the solder joint transition from the in situ reaction zone to the Cu-side interfacial reaction zone, the fracture mechanism shifted from brittle fracture to mixed brittle-ductile fracture, and then back to brittle fracture.</p>