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

A B

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Figure 1. (A) Aerosol jet printing system (Reprinted with permission from . Copyright (2019) American Chemical Society. (B) Intense pulsed light
system.
process. In this work, electrical property and the degree of described by the surface roughness parameters. It should
delamination are the two main optimization objectives. be noted that different surface roughness parameters are
As such, electrical property characterization and surface often used to describe different types of defects or surface
roughness characterization were conducted to provide anomaly. For instance, R measures the average deviation of
a
information about the sheet resistance and the degree of the surface over a sampling area (Figure 2A), R measures
z
delamination of the sintered film, respectively. the maximum deviation of the surface over a sampling area
The electrical property was measured using a Lucas (Figure 2B), and R measures the fourth power of the root
ku
Labs Pro 4 collinear probe station with a Keithley 2400 mean square deviation to display the dimensionless fourth
source meter unit. The measurements were done with the power of the sampling area (Figure 2C).
collinear probes placed at the center of each printed circular Each of these roughness parameters has its pros and cons
film. In this work, sheet resistance was used to characterize in terms of describing the severity of the delamination. For
the electrical property of the sintered film for a few reasons. example, R is useful for describing the overall severity of
a
First, it is almost impossible to calculate the resistivity of the the delamination but difficult to pick up small or localized
sintered film with swelling and delamination morphology delamination, whereas R is useful for describing localized
z
as the cross section of the film cannot be determined out-of-plane delamination but tend to overestimate the
accurately using the equation ρ = RA/L (R: resistance, delamination severity of localized defects in relation to the
A: cross-sectional area, and L: length) due to the non- overall surface condition. R , on the other hand, is useful
ku
uniform cross-sectional area . Second, as IPL sintering for differentiating different defect morphologies. As the
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usually results in non-uniform sintering across the depth, delamination of the sintered film can happen in various
sheet resistance was used in this study instead of electrical ways, it is vital to use different surface roughness parameters
resistivity because sheet resistance is more meaningful in such as R , R , and R to account for the different modes
ku
z
a
terms of reflecting the actual electrical property of the IPL- of delamination. However, for the ease of the optimization
sintered films with different thicknesses. Furthermore, this process and analysis, a single surface roughness indicator
allows electrical circuit designers and engineers to easily is preferred over many different surface roughness
determine the number of print passes without the need for parameters. As such, we have adopted a surface roughness
quantifying the film thickness. indicator, S, as a linear sum of the normalized surface
The surface roughness characterization was performed roughness parameters multiplied by their assigned weights.
using a Keyence VK-X200 confocal microscope coupled In this case, we defined the surface roughness indicator,



with a ×10 magnification lens. The region of interest S = w R a + w R z + 3 ku with 0 <<1,S w 1 + w 2 + w R w 3 =1.
2
1
was selected to be at the center of the circular film. As Each surface roughness parameter was normalized
the dimensions of a single scan region is approximately with the highest values of respective surface roughness
1500 µm × 1000 µm, this can result in biased and selective parameters (R a,max = 25.6 µm, R x,max = 370.1 µm,
sampling. To avoid this, a large scanning region was created R ku,max = 172.0 µm) within the sample populations, and
by stitching nine different scan regions. This resulted in a the weights for each surface parameter are the same
scanned region with a dimension of 4500 µm × 3000 µm, (w = w = w =1/3) to ensure equal contributions to the
3
2
1
which can better reflect the overall surface condition over surface roughness indicator, S. To illustrate the correlation
the sintered film. The severity of the delamination can be between the adopted surface roughness indicator and the
Volume 1 Issue 2 (2022) 4 http://doi.org/10.18063/msam.v1i2.10