9 Copper Micro and Nano Particles Mixture for 3D Interconnection …
249
nano particles
micro particles
Fig. 9.19 SEM image shows the micro—and nano—particles arrangement in mixed paste
• Micro-particle arrangement: The micro-particles are assumed to be arranged in
the FCC structure. However, the micro-particles could move around randomly
during the paste preparing, mixing and sintering. Therefore, the actual interstitial
space may not follow the shape assumed in the model;
• Particle size: The micro-particle size is assumed to be fixed at 1 μm in the simulation. The size of the commercial copper micro-particles received is in a range
of 1–2 μm and the nano-particles size is also in a range of 20–80 nm;
• Particle agglomeration: It is assumed that all the particles shape are spherical but
the particles shape may not be strictly spherical after washing processes to remove
the oxide;
• Temperature variation: Micro-particles and nano-particles are subjected to thermal
dynamics during the sintering process. This is not considered in the simulation.
Those reasons may lead to the deviation between the simulation and experiment
results. From the SEM images as shown in Fig. 9.19, it is seen that the nano-particles
fill the spaces formed by the micro-particles clusters. This is a departure from the
assumption. The micro particle are more likely to fuse with each other, so could the
nano-particles. Since the nano-particles have smaller size, when the micro-particles
form porosity during sintering, the nano-particles can fill in those spaces and connect
each micro-particles cluster. That is the main reason for the observed improved
performance.
9.3.4 Summary
We prepared and tested the micro-, nano- and mixed pastes. The in situ resistance
measurement is first used to determine the transition temperature and electrical
conductivity. The mixed paste has the lowest transition temperature and resistance.
There is no irreversible resistance increase in both micro-particles and mixed pastes
249
nano particles
micro particles
Fig. 9.19 SEM image shows the micro—and nano—particles arrangement in mixed paste
• Micro-particle arrangement: The micro-particles are assumed to be arranged in
the FCC structure. However, the micro-particles could move around randomly
during the paste preparing, mixing and sintering. Therefore, the actual interstitial
space may not follow the shape assumed in the model;
• Particle size: The micro-particle size is assumed to be fixed at 1 μm in the simulation. The size of the commercial copper micro-particles received is in a range
of 1–2 μm and the nano-particles size is also in a range of 20–80 nm;
• Particle agglomeration: It is assumed that all the particles shape are spherical but
the particles shape may not be strictly spherical after washing processes to remove
the oxide;
• Temperature variation: Micro-particles and nano-particles are subjected to thermal
dynamics during the sintering process. This is not considered in the simulation.
Those reasons may lead to the deviation between the simulation and experiment
results. From the SEM images as shown in Fig. 9.19, it is seen that the nano-particles
fill the spaces formed by the micro-particles clusters. This is a departure from the
assumption. The micro particle are more likely to fuse with each other, so could the
nano-particles. Since the nano-particles have smaller size, when the micro-particles
form porosity during sintering, the nano-particles can fill in those spaces and connect
each micro-particles cluster. That is the main reason for the observed improved
performance.
9.3.4 Summary
We prepared and tested the micro-, nano- and mixed pastes. The in situ resistance
measurement is first used to determine the transition temperature and electrical
conductivity. The mixed paste has the lowest transition temperature and resistance.
There is no irreversible resistance increase in both micro-particles and mixed pastes