Abstract
The sintering of metal nanoparticles (NPs) has been widely studied in the field of nanotechnology, and low-temperature sintering has become the industry standard. In this study, a molecular dynamics (MD) model was established to study the sintering behaviour of silver NPs during low-temperature thermo-compression. Primarily, we studied the sintering process, in which the ratio of neck radius to particle radius (x/r) changes. Under a uniaxial pressure, the maximum ratio in the temperature range 420–425 K was 1. According to the change of x/r, the process can be broken down into three stages: the neck-formation stage, neck-growth stage, and neck-stability stage. In addition, the relationship between potential energy, internal stress, and dislocation density during sintering is discussed. The results showed that cycling internal stress played an important role in sintering. Under the uniaxial pressure, the stress-dislocation interaction was found to be the major mechanism for thermo-compression sintering because the plastic deformation product dislocation intensified the diffusion of atoms. Also, the displacement vector, the mean square displacement, and the changing crystal structure during sintering were studied.
Highlights
The sintering of metal NPs has been widely used in the microelectronics industry, such as for pressureless bonding,[1] bonding copper pillars to copper pads,[2] and more generally in the construction of nanoscale devices.[3]
The mean square displacement (MSD) was calculated and the results are shown in Figs. 11 and 12
Low-temperature thermo-compression sintering was investigated by molecular dynamics (MD) simulation
Summary
The sintering of metal NPs has been widely used in the microelectronics industry, such as for pressureless bonding,[1] bonding copper pillars to copper pads,[2] and more generally in the construction of nanoscale devices.[3]. It takes a longer time to form necks with larger particles.[17] Arcidiacono et al found that when particles are larger than 20 nm, grain boundary diffusion is the main sintering mechanism.[18] Pan et al summarised the major neck growth mechanisms during the laser sintering of different sizes of gold NPs.[19] Zhu et al simulated the sintering of a copper cylinder at 1100 K with pressures of up to 4 GPa and found that a high initial packing density and pressure enhanced the sintering densification.[20] Cheng et al found that smaller copper NPs are easy to densify together, but the gap between NPs was slightly inhibitory.[21].
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