THESIS
2022
1 online resource (xvii, 98 pages) : illustrations (some color)
Abstract
Metal-based pastes are widely used in printed electronics for fabricating
conductive paths. Possessing low cost and valuable properties such as good
conductivity and electromigration resistance, nickel-based pastes can potentially
replace the conventional silver pastes for selected applications. This thesis aims at
systematically developing high-quality nickel-based conductive pastes, and includes
paste nanoparticle filler synthesis, paste formulation and sintering of the screen-printed
film.
In Chapter 2, a dual-reductant method was developed for synthesizing fine nickel
nanoparticles. The size of nickel nanoparticles could be well controlled within the range
of 11 to 48 nm, and a high product yield of 86.5% was obtained. Also, the synthesized
nickel nanoparticles in combination with n...[
Read more ]
Metal-based pastes are widely used in printed electronics for fabricating
conductive paths. Possessing low cost and valuable properties such as good
conductivity and electromigration resistance, nickel-based pastes can potentially
replace the conventional silver pastes for selected applications. This thesis aims at
systematically developing high-quality nickel-based conductive pastes, and includes
paste nanoparticle filler synthesis, paste formulation and sintering of the screen-printed
film.
In Chapter 2, a dual-reductant method was developed for synthesizing fine nickel
nanoparticles. The size of nickel nanoparticles could be well controlled within the range
of 11 to 48 nm, and a high product yield of 86.5% was obtained. Also, the synthesized
nickel nanoparticles in combination with nickel microparticles were utilized for the
formulation of bimodal pastes for screen-printing. A micro-to-nano particle weight ratio
of 2 was found to be the optimal ratio for achieving good electrical conductivity (122
μΩ∙cm) of printed films after sintering at a targeted low temperature of 600 ℃.
Next, in Chapter 3, a novel facile solvent-directed chemical reduction method was
developed for the synthesis of nickel nanoparticles with bimodal size distribution in
one-pot. Through simply adjusting the volume ratio of alcohol to water and nickel precursor concentration in a mixed solvent system, the size and size distribution of the
nickel nanoparticles could be controlled. The bimodal nickel nanoparticles obtained at
a volume ratio of methanol to water of 2 were then used as fillers for a screen-printing
paste. Enhanced mixing and dispersing could be avoided which are required for the
conventional bimodal paste preparation with using two different-sized particles
synthesized from separate batches. After sintering at a temperature of 600 ℃, the
printed film exhibited a compact structure with a relatively low volume resistivity of
167.3 μΩ∙cm.
For fulfilling the requirements of miniaturization and high integration of high-power
devices in printed electronics, thin nickel conductive films are desired. Nickel
pastes containing bimodal nickel nanoparticle fillers with size less than 100 nm were
formulated in Chapter 4. The filler size ratio was optimized. Applying the optimized
bimodal paste onto an alumina substrate, the resulting nickel film had a volume
resistivity of 29.8 μΩ∙cm and a thickness of 4.9 μm after sintering at 1100 ℃. Applying
the same paste to alumina green sheet, a 3.1μm thick ultra-thin nickel electrode film
was fabricated while ensuring an excellent electrical conductivity (12.9 μΩ∙cm) after
co-sintering process at 1100 ℃. The shrinkage mismatch between the nickel layer and
the ceramic layer was effectively mitigated.
In Chapter 5, nickel nanoparticles with tunable sizes over a wide range from 14.5
to 180.6 nm with narrow size distributions were prepared via facile chemical reduction
routes. It was achieved by precisely controlling the reaction conditions, including the
addition of NaBH
4, hydrazine concentration, reaction temperature, volume ratio of
mixed solvents and nickel precursor concentration. Then, a trimodal nickel paste
composed of nickel nanoparticles and microparticles with a particle size ratio of 1: 5:
50 and a mass ratio of 12.2: 22.0: 65.8 (from small to large particles) was prepared.
After sintering at a temperature of 1100 ℃, the printed nickel film exhibited a dense
structure with a volume resistivity of 18.8 μΩ∙cm.
Post a Comment