Particle Size Effects of Nano-Ag Films on the Interface Sintered Bonding for Die Attachment

Three nano-Ag films with different particle size distribution were fabricated as die-attach materials by pulsed laser deposition (PLD) using nanosecond (ns), picosecond (ps), and femtosecond (fs) lasers. The effects of interface bonding of the three films on shear strength and fracture behaviors were systematically studied. The investigation of the interfacial neck growth mechanism of the PLD films with different particle size provided insight into the formation process of the bonding interface. The results showed that when the laser pulse duration decreased from ns to fs, the average particle size decreased and the shear strength of the joints increased significantly. The fs-film presented extremely high shear strength of 147 MPa at 250 degrees C, 3.2 times and 2.0 times higher than the ns-film (46 MPa) and the ps-film (75 MPa), respectively, and well above most reports. The interface connection ratio was the dominant factor affecting shear strength and fracture behaviors. The interfacial neck growth of the fs-film was much faster than the ns-film due to its high surface and grain boundary energy. At the later sintering stage, the high grain boundary energy of the fs-film drove the neck merging and eliminated the gaps between the necks, resulting in the high interface connection ratio. The investigation of the interfacial neck growth mechanism can provide new guidance for interface bonding enhancement.