9 Copper Micro and Nano Particles Mixture for 3D Interconnection …
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packing density against the smaller sphere radius, it is found that the critical radius is
52 nm. This means that if the nano-particle radius selection ranges from x to 52 nm,
x is the best value; if the radius ranges from 52 to 100 nm, then 53.59 nm is the
best value according to our simulation results. Since the nano-particles used in our
exeriments is ~40 nm on average, we select the smallest size that would most likely
ensure maximum packing density.
9.2.3 Conclusion
The modelling algorithm and 3D simulation based on Monte Carlo Method are introduced to find the best mixture volume ratio between micro—and nano—particles. It
is found that the smaller particles size results in a larger packing density when nanoparticles size is below 52 nm. The reverse calculation is needed to find the weight
ratio between the micro—and nano—particles. This simulation has several assumptions and limitations. It is assumed that the nano-particles fill in the interstice and
change their arrangement until the maximum packing density is reached. Also, the
bigger spheres which represent micro-particles have fixed position and size. Nevertheless, the simulation gives an overall impression of the ratio between micro—and
nano—particles and it provides useful guidance for the subsequent experiment.
9.3 Cu Paste Formulation and Characterization
Copper paste formulation is an important step that could have direct consequences
on the paste performance during the bonding process. For metallic bonding, lower
sintering temperature and higher electrical conductivity are two important factors to
be considered. The solvents and additives used in copper particles should have a low
boiling point. Paste using some common solvents, such as α-terpineol [32], ethanol
[33] and hydrazine monohydrate & citric acid monohydrate [34], have sintering
temperature at about ~300 °C, which is considered high for the back-end interconnections in 3D IC. In this section, we first introduce the paste preparation method and
investigate how the mixed paste can have improvement on both thermal and electrical performance than the mirco—and nano—particles paste. In situ temperature
and resistance measurement, sheet resistance and SEM image analysis are utilized as
the characterization techniques. Paste with different mixture ratios are also prepared
and tested to find the optimum mixture ratio.
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packing density against the smaller sphere radius, it is found that the critical radius is
52 nm. This means that if the nano-particle radius selection ranges from x to 52 nm,
x is the best value; if the radius ranges from 52 to 100 nm, then 53.59 nm is the
best value according to our simulation results. Since the nano-particles used in our
exeriments is ~40 nm on average, we select the smallest size that would most likely
ensure maximum packing density.
9.2.3 Conclusion
The modelling algorithm and 3D simulation based on Monte Carlo Method are introduced to find the best mixture volume ratio between micro—and nano—particles. It
is found that the smaller particles size results in a larger packing density when nanoparticles size is below 52 nm. The reverse calculation is needed to find the weight
ratio between the micro—and nano—particles. This simulation has several assumptions and limitations. It is assumed that the nano-particles fill in the interstice and
change their arrangement until the maximum packing density is reached. Also, the
bigger spheres which represent micro-particles have fixed position and size. Nevertheless, the simulation gives an overall impression of the ratio between micro—and
nano—particles and it provides useful guidance for the subsequent experiment.
9.3 Cu Paste Formulation and Characterization
Copper paste formulation is an important step that could have direct consequences
on the paste performance during the bonding process. For metallic bonding, lower
sintering temperature and higher electrical conductivity are two important factors to
be considered. The solvents and additives used in copper particles should have a low
boiling point. Paste using some common solvents, such as α-terpineol [32], ethanol
[33] and hydrazine monohydrate & citric acid monohydrate [34], have sintering
temperature at about ~300 °C, which is considered high for the back-end interconnections in 3D IC. In this section, we first introduce the paste preparation method and
investigate how the mixed paste can have improvement on both thermal and electrical performance than the mirco—and nano—particles paste. In situ temperature
and resistance measurement, sheet resistance and SEM image analysis are utilized as
the characterization techniques. Paste with different mixture ratios are also prepared
and tested to find the optimum mixture ratio.