Page 34 - MSAM-1-2

Materials Science in Additive Manufacturing Intense pulsed light sintering of conductive film

In this work, we explore the use of IPL sintering technique Polyimide substrate was used in this work because it
for sintering aerosol jet printed silver nanoparticle film is widely used in the field of printed electronics for the
for printed electronics applications. Although there have fabrication of flexible electronics and wearables due to the
been many works that investigate the effect of various good material property and thermal compatibility. The
process parameters on the performance silver nanoparticle polyimide substrate was first cleaned with soap water and
film [34-39] , no study has investigated the interplay between ethanol to remove the inorganic and organic contaminants
the sintering parameters and film thickness on the quality on its surface. This was done to ensure that the surface
and the performance of the sintered film. The objective wettability of the surface was uniform to ensure consistent
of this work is to find out the process window of the IPL print quality and film adhesion. No surface modification
sintering process to achieve crack-free films with low was done on the polyimide substrate.
sheet resistance for aerosol jet printed film with different
thicknesses. To better analyze the correlation between 2.2. Fabrication of test coupons
different factors such as sintering distance and print passes Each test coupon is made up of four conductive thin film
on the surface morphology and electrical property of printed on polyimide films which can ensure at least a
the printed film, a multi-objective optimization method sample size of n = 3 for each test condition for statistically
was adopted. Here, a modified central composite design meaningful analysis. The diameter of the coupon is 1 cm.
(CCD) was used to study the relationships between the The tool path for the print head is designed to have a line
quality of the sintered films and the main printing and pitch of 120 µm to ensure sufficient overlapping between the
sintering parameters. Analysis of variance (ANOVA) adjacent lines for formation of homogeneous film. A spiral
was conducted to examine individual effects and the tool path design was used for the 1 cm diameter circles. The
interactions of the main variables on the sheet resistance printing of ink was done using an Optomec™ Aerosol jet ®
and surface roughness of the sintered thin films. The 5X system (Figure 1A). Ultrasonic atomizer was used for
results of analysis suggest that the CCD-derived models the printing of silver ink. For good printability, the process
are statistically meaningful. The modified CCD-derived parameters for printing the silver ink onto the polyimide
models were then optimized by a desirability function film were optimized to be as follows: sheath flow = 20
method, and a 2-dimensional (2D) optimal printing and standard cubic centimeters per minute (sccm), atomizer
sintering window were determined to yield thin film with flow = 50 sccm, ultrasonic atomizer current = 0.6 A, print
low sheet resistance and low surface roughness. Following speed = 10 mm/s, and the substrate temperature = 80°C.
that, the derived statistical models were jointly driven
with a non-dominated sorting genetic algorithm (GA) 2.3. Intense pulse light sintering of printed silver
to systematically optimize the conflicting responses in film
a more robust manner. The findings demonstrate the The sintering of the printed silver nanoparticle film was
effectiveness of the suggested multi-objective optimization carried out using a Xenon™ S-1000 pulsed light system.
approach in reducing the conflicting responses. This work The IPL sintering system consists of a tabletop controller,
presents useful guide for future attempts to optimize the a sintering chamber, and an air-cooled lamp housing
IPL sintering parameters for various nanoparticle-based (Figure 1B). The lamp operating voltage ranges from 2.25 to
film such as gold for good electrical conductivity and low 3.80 kV. The generated pulsed light has a pulse duration of
surface roughness for fast fabrication of multi-layered 520 µs and a pulse energy ranging from 290 to 830 Joules/
electronics such as electrochemical electrodes. pulse depending on the lamp operating voltage. The
in-house-made sintering chamber consists of a chamber
2. Materials and methods that houses the sintering lamp and a height-adjustable
stage. The chamber serves to prevent stray light from
2.1. Materials entering the lab and the height-adjustable stage allows for
The silver nanoparticle ink that was used in this work is the adjustment of pulse light intensity by controlling the
UT Dots Ag40TE purchased from UT Dots . The silver distance of the sample from the light source. As the light
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nanoparticle is reported to have an average particle intensity varies spatially, all the test coupons are placed at
diameter of 10 nm and it is dispersed in proprietary the center of the stage and sintered with five light pulses to
solvents. The optimum sintering temperature of the ink ensure consistency.
using conventional thermal sintering method is claimed
to range from 150°C to 200°C for at least 30 min. For 2.4. Characterization methodology
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the substrate, Kapton polyimide films with a thickness Characterization of the printed film was performed to
of 75 µm were used for the fabrication of test coupons. generate information that can be used for the optimization

Volume 1 Issue 2 (2022) 3 http://doi.org/10.18063/msam.v1i2.10