Nanotechnology
You may also like
PAPER • OPEN ACCESS
Implementation of microcontroller board on a
sustainable and degradable PLA/flax composite
substrate: a case study
To cite this article: Attila Géczy et al 2024 Nanotechnology 35 435201
View the article online for updates and enhancements.
- CircuitQ: an open-source toolbox for
superconducting circuits
Philipp Aumann, Tim Menke, William D
Oliver et al.
- GaAs0.95P0.05 single junction solar cell
with InP QW in p-i-n region for subbandgap photon absorption
Manish Verma, Soumya R Routray, Girija
Shanker Sahoo et al.
- Application of High-voltage Circuit Breaker
Status Evaluation Method Based on
Primary and Secondary Integrated Switch
Detection Platform
Xinyu Zhang, Yu Nie, Chuanzong Zhao et
al.
This content was downloaded from IP address 152.66.184.111 on 22/10/2024 at 09:23
Nanotechnology
Nanotechnology 35 (2024) 435201 (12pp)
https://doi.org/10.1088/1361-6528/ad66d3
Implementation of microcontroller board
on a sustainable and degradable
PLA/flax composite substrate: a case
study
Attila Géczy1,2,∗, Dániel Piffkó1, Richárd Berényi1, Karel Dusek2, Pascal Xavier3
and David Cuartielles4
1
Department of Electronics Technology, Faculty of Electronic Engineering and Informatics, Budapest
University of Technology and Economics, Budapest, Hungary
2
Department of Electrotechnology, Faculty of Electrical Engineering, Czech Technical University in
Prague, Prague, Czech Republic
3
IMEP LAHC, University Grenoble Alpes, Universite´Savoie Mont-Blanc, CNRS, 38000 Grenoble,
France
4
Arduino Verkstad AB, Malmö 211 77, Sweden
E-mail: geczy.attila@vik.bme.hu
Received 19 February 2024, revised 24 June 2024
Accepted for publication 23 July 2024
Published 5 August 2024
Abstract
In this paper, we present a novel polylactic-acid/flax-composite substrate and the
implementation of a demonstrator: a microcontroller board based on commercial design. The
substrate is developed for printed circuit board (PCB) applications. The pre-preg is
biodegradable, reinforced, and flame-retarded. The novel material was developed to counter the
increasing amount of e-waste and to improve the sustainability of the microelectronics sector.
The motivation was to present a working circuit in commercial complexity that can be
implemented on a rigid substrate made of natural, bio-based materials with a structure very
similar to the widely used Flame Retardant Class 4 (FR4) substrate at an early technological
readiness level (2–3). The circuit design is based on the Arduino Nano open-source
microcontroller board design so that the demonstration could be programmable and easy to fit
into education, IoT applications, and embedded designs. During the work, the design was
optimized at the level of layout. The copper-clad pre-preg was then prepared and processed with
subtractive printed wiring technology and through hole plating. The traditional surface
mounting methodology was applied for assembly. The resulting yield of PCB production was
around 50%. Signal analysis was successful with analogue data acquisition (voltage) and
low-frequency (4 kHz) tests, indistinguishable from sample FR4 boards. Eventually, the samples
were subjected to highly accelerated stress test (HAST). HAST tests revealed limitations
compared to traditional FR4 printed circuit materials. After six cycles, the weight loss was
around 30% in the case of PLA/Flax, and as three-point bending tests showed, the possible
ultimate strength (25 MPa at a flexural state) was reduced by 80%. Finally, the sustainability
∗
Author to whom any correspondence should be addressed.
Original content from this work may be used under the terms
of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the
title of the work, journal citation and DOI.
1
© 2024 The Author(s). Published by IOP Publishing Ltd
Nanotechnology 35 (2024) 435201
A Géczy et al
aspect was assessed, where we found that ∼95 vol% and ∼90 wt% of the traditional substrate
can be substituted, significantly easing the load of waste on the environment.
Keywords: biodegradable, PCB, commercial electronics, educational electronics, Arduino Nano,
PLA composite, single-board microcontroller
1. Introduction
Larguech et al [12] performed thermal and dielectric analysis on PLA/PBS (polybutylene succinate) blend matrix
after jute fibre reinforcement. At low temperatures, dielectric
permittivity was improved after reinforcement of the blend
matrix. The study by Kumar and Gupta [13] compared classical Flame Retardant Class 4 (FR4) with jute and epoxy,
sisal and epoxy, and hemp and epoxy-based potential composite materials. The results showed that the combination of
epoxy and jute, sisal, or hemp has almost the same properties as classical FR4. However, the authors did not address
the issue of flame retardancy, which is a critical aspect of
natural-based fibres. Ryan-Fogarty et al [7] proposed a new
composite material for PCB fabrication by recycling methods
to recover components from PLA boards. The process successfully separated the electronic components, copper bands,
glass fibres and polylactic-acid. However, glass fibre is a
weak point as long as it requires separate treatment during
recycling and cannot be composted. Bharath et al [14] proposed the incorporation of banana fabric as reinforcement,
but their work did not show more advanced application case
studies.
Yedrissov et al [15] demonstrated PCB manufacturing from
recycled and renewable materials, where various components
were recovered during the process. Sudheshwar et al [16,
17] have proposed paper-based electronics with additive patterning. Arroyos et al [18] produced a prototype computer
mouse consisting of a biodegradable PCB, a compostable
PVA case, and a limited set of electronic components. The
applied Soluboard PCBs and the PVA case were dissolved in
water, and after disassembly, many of the components could
be reused. However, from a commercial point of view, solubility seems to be a limiting factor, and water is a central point
of reliability issues related to assemblies [19].
In our previous studies, we successfully produced PLA and
CA-based RFID cards in different sizes Kovács et al [20], and
a media player as a commercial application was presented.
Fibre reinforcement and solder mask applicability was lacking, and the assemblies presented were very sensitive to conventional reflow (reflow soldering) temperatures, even with
Sn–Bi-based solder alloys at reduced melting point (138 ◦ C).
We improved this with the introduction of the PLA/Flax composite with flame retardancy, which showed promise in biodegradability of the carrier substrate, application in surfacemounted technology (SMT), sustainability, reliability, and the
missing parameters, namely fibre reinforcement and flame
retardancy [21].
Electronic devices are an essential part of our modern and
evolving world; the number of circuits is constantly growing due to the ever-increasing demand. The lifetime of these
circuits, however, is not unlimited. At the end of their life
cycle, most electronic devices end as hazardous waste. The
amount of e-waste is around 60 million tonnes annually and
is projected to increase by 2 million tonnes annually [1, 2].
Asia has the highest e-waste production, while Europe has
the highest e-waste per capital. Approximately 10% of waste
is diverted, mostly illegally, to poor developing countries to
recycle valuable metals that can be recovered from e-waste
back into the trade [3]. However, exposure to highly toxic
substances and untimely and unskilled work processes can
shorten the lives of people involved by decades [4]. The
Brundtland Report [5], published by the United Nations in
1987, defines sustainable development as ‘development that
meets the needs of the present without compromising the ability of future generations to meet their own needs.’ According
to the strict sustainability model, increasing economic capital can only be at the expense of natural capital, which cannot be increased and includes economic and social capital, as
these are part of our environment as subsets of it. The current electronics industry cannot be sustained in the long term,
as our raw materials resources and waste storage capacity are
finite.
From this aspect, one possible point of easing the load
on the environment and resources is to find alternative technologies and materials in electronics, such as focusing on
packaging materials. In recent studies (Khrustalev et al) [6],
it was found that about 70 wt% of the waste printed circuit board (PCB) generated is glass fibre reinforced epoxy
composites, which are difficult to process and harmful to the
environment if left in e-waste piles. Metals can be recovered
from the composites by hydrometallurgical, mechanical, or
pyromechanical treatment—also problematic regarding environmental impact (Ryan et al) [7]. Thus, many focus on
this aspect in their studies. The development of sustainable
electronics is mainly based on polylactic acid (PLA) substrates. This use has been investigated from several perspectives in recent years (Schramm et al [8], Mattana et al [9],
Henning et al [10], Hong et al) [11]. However, many studies
have omitted flame retardancy and fibre reinforcement (even
more, the combination of the two), leading to more reliable
assemblies.
2
Nanotechnology 35 (2024) 435201
A Géczy et al
Figure 1. The cross section of the substrate presents the structure (thicker inner textile, refined outer textile) and through-hole vias (with
fibre-based burrs).
According to the findings above, we focus on the following in our current research. We wanted to validate our novel
substrate promoting degradability with a feasible and straightforward application of current technologies and features. The
current paper presents the implementation of a small footprint
controller board on a sustainable PLA/Flax composite biodegradable substrate, starting from surface mounting assembly
to actual tests of the microcontroller board. The presented
complexity (to be discussed later) is intended to be higher
than what we could obtain from the literature. The exemplary
application also promotes sustainability, where the expected
reduction of actual wt% of generated e-waste [7] is above 70%
with completely degradable substrates. With the application
of an Ardunio Nano microcontroller board [22], we choose
an example where commercial complexity could be achieved
with a widely used circuit (released under Creative Commons
Attribution Share Alike 3.0 License).
The PCB substrate is a result of a collaboration between
BME-ETT and Meshlin Composites Zrt [21].
2.2. Experimental steps
The following experimental was set to present the research
implementing the commercial complexity circuitry on the sustainable bio-substrates. The mind map of the experiment is
presented in figure 2.
First, the analysis and optimization of the adopted circuit design were considered in CAD software to avoid errors,
which could arise from previously investigated material parameters, such as surface roughness [21]. We used the original
files. While we are not at the technical readiness level (TRL)
of the technology to have exact design rules for our technology
limitations, we tried to polish the design, so that any possible
failures would be minimized. The full documentation, schematic and layout design can be accessed at [25].
Afterward, subtractive PCB technology was used to prepare
double sided printed wiring on traditional FR4 and PLA/Flax
boards. The copper clad was processed with photolitography
and copper etching processes. The technology steps are using
plated through-holes (Dow chemicals and Crimson direct
electroplating) and selective chemical surface finish (ImAg,
immersion silver, ∼0,5 µm thickness) according to the technology steps of our laboratory [26]. It has to be noted, that the
plating of through hole is aimed for 25 µm thickness, which
adds up to the copper thickness on the top and bottom layers (∼60 µm thickness altogether). This, and the evenness of
top/bottom layers, and the unevenness of the through hole platings can be also seen in figure 1.
Finally, traditional photosensitive solder mask is printed
(SunChemicals, Imagecure, XV501T) to improve soldering of
surface mounted components, albeit reducing the degradablenon degradable ratio of applied materials. The mask is finished
with 150 ◦ C/60 min baking process.
Laser-cut (Coherent Avia UV Nd:YAG) stencil (100 µm
thick) was used for stencil printing with low-temperature
Sn42/Bi57.6/Ag0.4 (no-clean, T4 type, melting point: 138 ◦ C)
Tin–Bismuth solder alloy (Chipquik, SMDLTLFP60T4).
2. Experimental
2.1. Biodegradable substrate
The structural design of the substrate and the common FR4
composite are similar but mainly differ in the materials used.
The FR4 substrate is a glass fibre-reinforced epoxy resin composite with flame retardants. In the case of the degradable substrate used, the glass fibre is replaced by a set of flax fibre
textile fabric (grammage between ∼200–300 g m−2 ), and the
epoxy resin is replaced by polylactic acid, presented in powder
and foil form. The novel composite is flame retarded with natural retardants. The current application improved upon previously published versions using linseed oil to reduce water
absorption possibility, which was found to be a problem in
initial experiments [21].
Figure 1 presents a cross-sectional view of the degradable composite, showing the structure of the substrate and the
materials used.
In table 1 we have added a summary of available and comparable (with FR4) material parameters according to their
practical unit highlights in given literature.
3
Nanotechnology 35 (2024) 435201
A Géczy et al
Table 1. Parameter comparison.
Parameter, unit
PLA/Flax [21, 22]
FR4 [23, 24]
Dielectric Thickness, mm
Starting copper Thickness, µm
Effective Permittivity @ 2–2.4 GHz
Loss Tangent @ 2–2.4 GHz
Peel strength, N/mm
Flame-retardancy
Tg, ◦ C
Thermal Diffusivity, cm2/s
1,6 (see figure 2.)
35
∼2.3 ± 0,1 (2,4 GHz)
∼0,04 ± 0,01 (2,4 GHz)
∼0,6–0,8
UL94 V0, EN 13 501–1
∼60–100
0.000 565
1,6 (variable)
35 (variable)
3,93 (2 GHz)
0.0167 (2 GHz)
1,19–1,6
UL94 V0
170
0.0027
Figure 2. Mind map of the experimental—from goal to finish (CAM rework, PCB substrate fabrication, SMT assembly, yield analysis,
functional tests, HAST, and mechanical tests.
Manual component placement was performed on the
boards. With programmed profiles, the soldering was performed for both sample types in a computer-controlled, laboratory bench-top infrared-oven (Eurocircuit, ec-Reflow-Mate)
suitable for prototyping. The oven is working in laboratory
air environment, and was found to be suitable for controlled
low-temperature settings and experimenting at early TRL.
Through-hole soldering was performed with hot iron soldering (Bakon 938 hand soldering station, operated at 300 ◦ C)
after validating more drastic point-like heating on the boards.
Figure 3 presents the reflow profiles considered for measurement set in the Eurocircuits oven software. The primary considerations for the profile settings were to minimise the time
and to set the maximum temperature as low as possible. Also,
the most critical component (ATMEGA168P-20MU, QFN;
500 µm pitch with 230 µm pads) had to be joined succesfully.
To quantify the effect of applied temperature profiles, heating factors (Qη) were calculated [27]. The following equation
is used to determine the heating factor (1):
tˆ
A,B,C
(T (t) − TX ) dt
Qη =
(1)
t0
where Qη is the heating factor [s◦ C], practically the effect of
temperature in time on the board, T(t) is the measured temperature, Tx is the boundary temperature (usually the liquidus
of the solder), t0 to tA is the time window from entering and
passing the boundary temperature during heating and cooling
[s]. The cooling was performed on natural ambient convection
after finishing with the profiles.
4
Nanotechnology 35 (2024) 435201
A Géczy et al
Figure 3. Programmed temperature profiles applied for soldering. The soldering was performed with IR-based reflow heating.
Table 2. Main design rules and final board parameters defined for
The cross-section (X-cut) of samples was prepared with an
ATA Saphir 520 wet grinder. For optical inspection, Olympus
BX51 microscopes were used with Olympus DP72 cameras;
for non-destructive x-ray analysis, Nordson Dage Quadra 5
microscope was used. For contact measurements, a Gossen
Metrawatt METRA HIT 30 M-type multimeter was used. The
short-tests and x-ray analysis revealed the validity of plated
through holes too, while cracks or delaminations in similar
environmentally friendly substrate materials [28] can cause
hidden problems around these features.
The technological steps can be seen in greater details in
[26], starting from a copper-clad laminate for two-sided boards
with through-hole vias.
The bootloader is a fixed background code that controls the
controller and allows the device to be programmed easily from
the ArduinoIDE interface. An official Arduino Nano microcontroller was used for programming. A simple interstitial circuit was developed for this step that connects the corresponding legs of the microcontrollers. The defined sample programs
were written to test the digital and analogue voltage output,
analogue voltage input (data acquisition), and serial communication over USB. For these tests, a program reads the voltage
of a 1000 µF capacitor connected to its input, slowly losing its
charge through a resistor, causing its voltage to decrease over
time. With one pin configured as an output, the microcontroller recharges the capacitor for 1 s at a given time step. We connected an LED to a PWM-compatible output leg to optically
test working, where LED brightness gradually decreased as the
capacitor slowly discharged. Testing was extended with signal
generation analysis (sinusoidal, 4 kHz) reading and eventual
processing in Matlab.
Finally, highly accelerated stress test (HAST) extreme
environmental load analysis was applied. This test method
exposes the tested circuits to the most extreme environmental
parameters. We used Espec, EHS-211 HAST chamber in the
test, with unassembled circuits. The carriers were exposed to
extreme conditions for a total of 6 d. The condition of the circuits was checked daily. The total weight of the PLA/Flax and
control FR4 substrates was documented. The cycle parameters were set to a minimum temperature of 105 ◦ C and 100%
humidity. The chamber automatically sets the required pressure to achieve the desired temperature and humidity. The
pressure value for the set parameters was 120% of atmospheric pressure. The weight data of the examined boards
the layout.
Design rule/Parameter, unit
Value
Number of copper layers
Copper trace width (min), mm (mil)
Copper to copper, mm (mil)
Edge keepout, mm
Minimum component pitch, mm
Minimum via diameter, mm
Number of Vias
Number of Signal lines
Longest signal line, mm
Number of Pads
Size of the board, mm
2 (top and bottom)
0.254 (10 mil)
0.203 (8 mil)
0.4 mm
0.5 mm
0.5 mm
41
43
82.85
125
43.2 × 18
were registered with a Radwag PS 210. R2 precision laboratory scale (Radom, Poland) with 10 µg certified precision,
1 µg readability, and repeatability in the ambient environment.
After HAST, 1–1 degradable and FR4 control samples and two
degradable and two FR4 treated samples were sent for 3-point
bending (Zwick Roell, DIN EN ISO 14125). The aim was to
visualize and quantify the extent to which the structure of the
substrates used in the experiment had weakened during the
HAST cycle.
2.3. Case study of design optimization
It was important to minimize via count and irregular shapes
in the design to minimize possible failures during production.
While we experimented with designs involving SOIC-8 (with
1.27 mm, 50 mil pitch) before [21], our current QFP package has 500 µm pitch and 230 µm wide pads, which requires
∼10 mil trace width.
So small copper fills with related vias were removed. The
original 0.2 mm edge keepout was increased from the board
outline to avoid delamination (0.4 mm). The minimum trace
width was increased to 10 mil (∼0.254 mm), and the copper to
copper was kept at 8 mil (∼0.203 mm). The main parameters
are presented in table 2
All trace-via connections were corrected to a regular
90 ± 45◦ angle to reduce possibility of improper etching.
Corner holes were switched to fiducial points to aid stencil alignment. Silk and solder mask layers were also further
5
Nanotechnology 35 (2024) 435201
A Géczy et al
Figure 5. FR4 control sample (top) and PLA/Flax sample (down).
Figure 6. Non-wetting solder balls on contact pads caused by
excess linseed oil precipitations.
All FR4 boards were found to be without errors by optical
inspections (as expected). During the inspection under the
microscope following the soldering, no short circuits, tears,
or other soldering defects were found on the FR4 samples.
Figure 5 presents the samples as a comparison between the
two assemblies.
The degradable composite, laminated with copper foil on
both sides, was produced as a sheet measuring approximately
30 × 40 cm. Examination of the substrate surface showed that
the copper layer is slightly inhomogeneous, with minor surface
voids observed, similar to the findings reported in [21]. Small
oil spots were observed on the surface of the degradable composite. The state of the linseed oil on the substrate was characterised as solid. Warming and wiping, petrol cleaning, or
upholstery cleaning spray did not remove the oil stains; however, we could remove the surface contamination with acetone.
The linseed oil could be removed from the surface by rubbing
the circuit’s surface with a lint-free wipe soaked in acetone.
During initial tests, we observed solder non-wetting (figure 6)
on several pads without cleaning. Wiping ceased these issues.
Figure 4. (a)–(b) Reduction of small copper fills and vias; (c)–(d.)
FR4 and PLA/flax representation of (b.)—practically identical
results; (e)–(f); simplification of intricate silk-screen layer; (g)–(h)
FR4 and PLA/flax representation of (f.)—practically identical
results.
optimised to avoid precision screen positioning requirements.
Examples are seen in following figure 4.
3. Results
3.1. Production results
Initially, ten pieces of boards were produced from FR4 and
PLA/Flax. Samples were prepared with the same assembly
manners (with traditional SAC305 Sn–Ag–Cu type solder
alloy and higher soldering temperatures). Both technologies
were evaluated according to the experimental plans.
6
Nanotechnology 35 (2024) 435201
A Géczy et al
Figure 7. Short failures on various x-ray images; comprehensive x-ray image of the circuit (top); short between D13 and GND (bottom
left); short between RST and GND (bottom right).
Table 3. Yield analysis of the produced batch.
No. of board
Observation
Short (pin-pin)
Consideration
1
2
3
4
5
6
Heavy contamination of linseed oil, excess shorting.
Clear surface
Miniscule spots of contamination
Heavy contamination of oil, a few contaminated vias
Clear surface
Miniscule spots of contamination
X
Workable
Workable
Workable
Workable
X
7
Clear surface
8
9
10
Miniscule spots of contamination
Heavy contamination, pad lifting
Clear surface
D11-D12; GND-RST-A4-AA5-A6-A7-5 V
GND-D13
—
—
GND-RST
GND-D3-D11-D13
D9-D10
GND-RX0-VIN
A5-A6-A7
A3-A6
GND-RST
GND-RST-D11-D13
Cross-section analysis (shown in figure 1) on the PLA/Flax
samples revealed that the through-holes have uneven surfaces
at the plating, which reduces the internal diameter of the vias.
The reinforcement causes this issue. During the currentless
hole metallization process, a layer of metal is deposited on the
wall of the hole with remaining burrs observed. This effect did
not cause any problems during assembly.
Nevertheless, the results are promising at this TRL level—
no similar board with effectively formed hole metallization
has yet been characterised in the literature. Our contact tests
showed that all vias performed without a failure over the number of boards, even when small spots of linseed oil residues
remained in the holes.
Further short circuit tests, however, revealed further failures
of production. In 8 of the 10 circuits tested, short circuits were
found; in 4 circuits, we found more than one short circuit. The
exact location of the short circuits could not be determined
with an optical microscope.
X-ray photographs of the short circuits found were taken
for documentation and to assist in rework. (x-ray is later also
used after surface mounting).
X
Workable
X
X
In one rendered image, both sides (top and bottom) plus the
through hole vias are visible for failure detection. Open circuits are also practical to detect with the contrast of the x-ray
images. We followed this step by mechanically brushing off
the located short circuits. After the correction steps, there was
no metallic contact between the previously contacting nets.
Figure 7 presents a set of shorts revealed by x-ray imaging, and
later, the obtained pictures also helped yield analysis (table 3).
The initial explanation for the existence of short circuits
was thought to be the short etch time of copper, which was
set to the standard FR4-based processes. However, the xray contrast should show a gradual thickness change; the
substrates examined had one or at most two short circuits.
If these were due to the shortness of the etch time, it is
unlikely that we would experience so few and so distinguishable short-circuit locations, while at other points in the
circuit, the copper patterns of the different conductors are
well separated, and there is a high contrast ratio between the
conductor-insulator. Also, a clear correlation between board
cleanliness and shorts could not be established. (As seen in
table 1).
7
Nanotechnology 35 (2024) 435201
A Géczy et al
Figure 8. Assembled circuit on PLA/Flax with pin rows.
It was concluded that vertical mask alignment issues due
to surface unevenness during subtractive printed wiring technology could cause the shorts, which could be eliminated
by using more prominent features in patterning or reducing
the surface roughness of the boards [21]. We know, that the
average roughness depth (Ra) were 5.77 µm and the average peak to valley height (Rz) of the dielectric surace were
∼16 µm according to ASME B46.1 and ISO 4287 standards
[21] of or PLA/Flax boards. These larger vales are due to occasional peaks and valleys in the composite. In case of FR4, the
Ra is below 1 µm [29], the latter parameter is slightly more
1 µm [30]. Reducing the roughness is a serious task of the
future. By optimizing the layer structure at the top and bottom
of the dielectric, and improving the copper-to-dielectric interface will result in a more evenly surface, and reduced maskmisalignment issues.
Summing up, the initial yield was 50% with rework and
post-processing, which aligns with the technological maturity
expected at this basic research stage.
Table 3 contains the summary of the yield analysis. The
pins are defined in the original documentation of the Arduino
Nano circuit [22].
The first two profiles had a more significant impact on the
boards. The elevated heating resulted in a slight excess of linseed oil; however, further contamination was avoided using
Profile C, and joints generally formed along the boards. With
elevated temperatures, a few minor errors were found. In one
case, solder wicking was found to cause a short between the
leads of the USB connector. Further rework was necessary
for the microcontroller package as well for one pin. Such
complications arose from minor contaminations from hightemperature oil spills, emphasizing the necessity of low temperature and proper cleaning. However, these are occasional,
not consequential issues.
Soldering the through-hole pin rows for the board was also
performed with hand soldering. The metalized fibrs in the
holes caused a slight resistance in pin insertion. The board
could withstand efficient hand soldering at 300 ◦ C with SAC
alloy at the pins without noticeable damage. The bootloader
program was successfully loaded onto the microcontrollers.
After soldering and subsequent rework, functional tests
followed—at this point, achieving a functioning circuit of this
complexity is a major achievement. Figure 8 presents a figure
of an assembled board on PLA/Flax circuit.
3.2. Solderability test of degradable circuits
3.3. Basic functional tests of biodegradable substrates
Different solder profiles were applied to perform component
and board joining (A, B, C as seen in figure 3). The following heating factors were calculated for the different profiles.
The first two profiles were programmed to have approximately
Qη A : 38 000 [s◦ C] and Qη B : 36 000 [s◦ C], and the third had
Qη C : 32 300 [s◦ C], a 15% reduction of heating compared to
profile A.
From the profile validation measurements (available from
the oven software) and calculations according to (1), we found
that the actual heating resulted in ∼5% lower Qη values. The
actual board temperature could not follow the oven’s transients completely; however, this can be considered a precise follow in reflow technologies. It also has to be noted that the calculations were not related to the usual temperature boundary
(solder alloy melting point) but were defined from the starting
point to the immediate cooling of the boards to reveal how the
total structure was affected by the whole heat applied to the
board.
The microcontroller’s internal oscillator is working, and this
is evident from the success of programming and running basic
programs. The question was what the microcontroller perceives from the outside world by detecting analogue signals,
without the need to prove high frequency operation, and thorough validation of the dielectric. The sampling frequency of
the system is 10 kHz with the analogRead() function. With
our calculations according to additional tasks performed by
the system, the sampling was found to be 8800 Hz approximately, so we chose a slightly lower value than half of this
frequency (4 kHz ultimately). Figure 9 shows the load and
discharge of the test capacitor—where the two boards were
practically indistinguishable. This proves the practical applicability of the substrate in such scenarios.
We used a function generator to connect a signal of known
frequency, voltage, and shape to one of the analogue input legs
of the microcontroller and sample the signal from the input.
From the resulting data, we plotted the frequency composition
8
Nanotechnology 35 (2024) 435201
A Géczy et al
the significantly higher degree of degradation of the substrates
is immediately apparent. They show delamination of the layers, delamination of the solder resist and assembly markings,
oxidation of the copper surfaces, and the appearance of PLA
as white porous contamination on the surface of the circuits.
Examining the tray on which the substrates were placed in the
HAST chamber, it is noticeable that the tray edge (on which
the substrates were degraded) was also heavily contaminated.
The measurement results also show a reduction in the weight
of the degradable substrates (figure 12.). It can be seen that
during the cycles, the mass of the carriers decreased monotonically, showing precipitating parts of the composite. The initial minimal increase in mass is due to minimal water absorption by the circuits due to 100% humidity. After six cycles,
the weight loss was around 30% in the case of PLA/Flax. The
effect of PLA and the linseed oil impregnate loss is validated by the discussed comparisons. The PLA has a density of
∼1,25 g cm−3 , linseed oil has ∼0,9 [31] at given temperature,
so the loss of PLA has to be a significant factor in the degradation, even if water moisture is absorbed by the structure.
In the case of FR4-based circuits, no heavy degradation
was observed optically. Between cycles, oxidised copper surfaces and a slight fading of the green colour of the solder mask
were observed. The mass measurements confirm this, since no
change was recorded after an initial mass increase.
In this case, the results can be seen from both pros and cons.
It is clear that the biodegradable substrates will prove with
low reliability in a harsh environment. The structure of the
novel material limits applicability in extreme environments,
but the test also showed that the board will not resist environmental factors during planned degradation, which is a positive
outcome. In an ambient environment, such effects will not be
observable.
The three-point bending test results reveal the changes
before and after HAST in figure 13, where the stress-strain
curve is shown for the PLA/Flax boards (reference without
HAST and two treated samples). The recorded ultimate
strength for control sample FR4 was ∼300 MPa, which
reduced to ∼200 MPa after the HAST cycles, meaning a
∼33% reduction in the original values. The figure shows
the untreated PLA/Flax substrates where ultimate strength
presents ∼25 MPa peak, which is much lower than the values
of FR4, suggesting weaker mechanical performance for this
kind of substrate. This was further reduced to below 5 MPa
after HAST (∼80% decrease), meaning HAST has a much
higher impact on the degradable boards.
Figure 9. Measurements PLA/Flax.
Figure 10. Comparison between FR4 (top) and PLA/Flax
measurements (bot), 4000 Hz 4Vpp, 2.5 V _off, SIN.
of the signal using Matlab’s (Fast Fourier Transform) function. As shown in figure 10, a 4 kHz sinusoidal signal with a
peak-to-peak of 4 V and an offset voltage of 2.5 V was applied
to the inputs of microcontrollers created on degradable and
FR4 substrates. According to the sampling rules, spikes in the
frequency spectrum are seen at 3960 and 4896 Hz. (Deviance
from optimal 4000 and 4800 Hz is due to the inaccuracies of
the utilized ADC in the microcontroller.) It can be seen that the
results obtained from the sampling data are practically indistinguishable, regardless of the substrate.
We conclude that the analogue circuit tests showed no differences at the given application level. We have verified that
operation is practically similar on both PLA/Flax and FR4based Arduino Nano systems; the basic functions work as
intended. This analysis is a complementary result to previous
findings in [25], where an FPGA functionality at higher speed
was investigated on a previous generation of our substrate.
4. Discussion on sustainability
According to the final Gerber files of the design containing the
copper surface, we determined that the substrate takes ∼95%
by volume (vol%) and ∼90% by weight (wt%) of the circuit structure. This means that in FR4-based PCBs, these proportions are associated with the epoxy-glass fibre composite
itself, which is complex and not environmentally friendly to
process when it becomes e-waste. The studied material completely replaces this composite. These figures indeed point to
3.4. HAST tests on the boards
After six days of HAST, comparing the images of the circuits
before the first cycle and after the last (6th) cycle (figure 11),
9
Nanotechnology 35 (2024) 435201
A Géczy et al
promote SDG 4 (Quality Education). The device could be
used in secondary and higher education classrooms as a green
electronics demonstrator, targeting a sensitive and receptive
audience.
5. Conclusions
We presented a successful case study on implementing a
microcontroller board on a sustainable PLA/Flax composite
biodegradable substrate. We have successfully created a functioning panel on a composite substrate of natural origin and
biodegradability with natural fibre reinforcement and flame
retardancy. The complexity of the panel is considered to be
in line with the commercial level for popular microcontroller
boards. We were able to boot an Arduino system and use
its functions. Similar circuit was not found in our literature
research by traditional subtractive printed wiring patterning
and SMD technology with biodegradable substrates.
It was found that mask alignment issues and minor surface unevenness caused occasional shorts at the formed copper
traces; however, most of the shorts could be reworked. 170 ◦ C
IR-based reflow was successful. Another issue was the contamination of the pads caused by the impregnated linseed oil,
which was removed with acetone. Later, the further spill was
avoided with careful heating, eliminating soldering failures.
Higher temperatures are not recommended due to the resulting spill contamination and thermal degradation of cellulosebased reinforcement.
PCB production was concluded with a 50% yield. QFNs
with 450 µm pitch and 170 µm pads were successfully
soldered.
Signal analysis was successful with analog voltage reading
and low-frequency (4 kHz) signal tests, practically showing
equivalent working behaviour with the reference FR4 samples.
HAST tests showed precipitations on the boards, showing leaving constituents (such as PLA and oil impregnate).
After six cycles, the weight loss was around 30% in the case
of PLA/Flax. After the cycles, the possible maximum load
(25 MPa at a flexural state) was reduced by 80%, resulting in
weak and brittle samples. The extreme ambiance is not suitable
for this kind of substrate; however, this also suggests that the
boards will degrade in longer-term exposure in proper environment; thus, future recycling of copper and components will
be possible.
One of the central values of the work from the side of sustainability is that by replacing the traditional FR4-based (fibreglass, epoxy resin) boards with our substrate, about 90% of the
volume and mass fraction of the total PCB assembly could be
replaced by a sustainable, environmentally friendly, naturally
sourced and degradable alternative (the substrate itself), which
is a revolutionary change in the e-waste impact of PCBs as
we know it today, as repeatedly demonstrated in the literature.
As for biodegradability, we have to note that PLA is effectively degradable only in closed and specific environment [32],
however flax-based textiles are more generally degradable.
The degrading processes should be in line with the requirements of PLA. Also it is important to note, that before actual
Figure 11. After HAST analysis.
a change in the impact and sustainability of e-waste, and the
current results (albeit with only two layers of PCBs) represent
an improvement over the ∼70% presented by (Khrustalev et al
2022). According to the current Gerber copper area analysis, it
is estimated that the vol% and wt% values (while maintaining
PCB thickness) will decrease with increasing the number of
copper layers (e.g. 4–6 layers) to 70–80%.
According to the UN Sustainability Development Goal
points (SDGs) [18], the results point to SDG9 (industry, innovation, and infrastructure), as we are striving for sustainability along all three concepts, with the same production infrastructures as used in current SMT production. In addition, the
drastic reduction of e-waste strengthens SDG 12 (responsible
consumption and production), further scaling up the attractiveness of the consumer side (‘green electronics’) and the
responsible use of raw materials in production, which can
have implications for more up to SDGs 13–15. If the Arduino
device were to be used for educational purposes, it could also
10
Nanotechnology 35 (2024) 435201
A Géczy et al
Figure 12. Weight change after HAST.
the possible application will be limited to more general, commercial use. These factors need further investigation, but the
results improve upon most similar work in the literature, not
focusing on water solubility [17] and maintaining degradability and stability.
In future works, we aim to achieve TRL4/TRL5 (TRL4–5
laboratory validated technology, pilot test) implementation of
the above concept. The current results were found to be satisfactory at the presented TRL2–3 level.
Data availability statement
All data that support the findings of this study are included
within the article (and any supplementary files).
Figure 13. Stress-strain curves of PLA/Flax.
Acknowledgments
We thank for the help of EFI-Labs in laboratory measurements. Supply of the substrates from Meshlin is highly appreciated. Focus on reflow and heat transfer was partially supported by the National Research, Development and Innovation
Office—NKFIH, OTKA Project no. FK 132186. The material and the demonstrator is in focus of of the DESIRE4EU
HORIZON-EIC-2023-PATHFINDERCHALLENGES-01-04
Project No. 101161251.
degradation process, the components and the conductors could
be mechanically separated. Bioleaching is also in our future
focus.”
In the future, separating copper and components would
allow easier recycling of non-degradable components. By
using this material, the ecologically demanding processing of
FR4 e-waste presented by Ryan (2023) [8] could be converted to more environmentally friendly solutions with a fully
degradable substrate.
The thorough reliability analysis of the material will be performed at higher TRL levels, where the quality and reliability
issues will be evaluated on substrate, track and plated through
hole via levels.
The main drawback of this technology is its slightly
reduced quality and reliability and poor environmental performance. The future may introduce further improvements
with the chosen textiles and impregnates (e.g. a possible
path would be to vary the impregnation oils and their postimpregnation handling), or to introduce inner copper layers to
improve mechanical performance, however this is an expansive path for the future. Also we have to understand, that HAST
is an extreme test of the material set; it has to be concluded that
ORCID iD
Attila Géczy  https://orcid.org/0000-0002-4125-8791
References
[1] Statista.com Projected electronic waste generation worldwide
from 2019 to 2030; Accessed 2024 January 27 (available at:
www.statista.com/statistics/1067081/generation-electronicwaste-globally-forecast/)
[2] Ruiz A 2023 Latest global E-waste statistics and what they tell
us Theroundup.org Accessed 2024 January 27 (available at:
https://theroundup.org/global-e-waste-statistics/)
[3] Debnath B, Roychowdhury P and Kundu R 2016 Proc.
Environ. Sci. 35 656–68
11
Nanotechnology 35 (2024) 435201
A Géczy et al
[4] Perkins D N, Brune Drisse M-N, Nxele T and D. Sly P 2014
Ann. Glob. Health 80 286–95
[5] Keeble B R 1988 Med. War 4 17–25
[6] Khrustalev D, Tirzhanov A, Khrustaleva A, Mustafin M and
Yedrissov A 2022 Sci. Rep. 12 22199
[7] Ryan-Fogarty Y, Baldé C P, Wagner M and Fitzpatrick C 2023
Resour. Conserv. Recycl. 191 106881
[8] Schramm R, Reinhardt A and Franke J 2012 Capability of
biopolymers in electronics manufacturing Proc. IEEE ISSE
(https://doi.org/10.1109/isse.2012.6273157)
[9] Mattana G, Briand G, Marette A, Quintero V A and de
Rooij N F 2015 Org. Electron. 17 77–86
[10] Henning C, Schmid A, Rückmar C, Zink P, Bauer R, Harre K
and Göbel G 2020 Proc. of IEEE ISSE (https://doi.org/
10.1109/isse49702.2020.9121011)
[11] Hong F, Myant C and Boyle D E 2021 Proc. 2021 CHI Conf.
on Human Factors in Computing Systems (https://doi.org/
10.1145/3411764.3445469)
[12] Larguech S, Triki A, Ramachandran M and Kallel A 2021 J.
Polym. Environ. 29 1240–56
[13] Kumar V and Gupta M 2021 Comparative study of different
natural fibre printed circuit board (PCB) composites Mater.
Today: Proc. 44 2097–101
[14] Bharath K N, Puttegowda M and Yashas Gowda T G
Arpitha G R Pradeep S Rangappa S M and Siengchin S
2023 Biomass Convers. Bioref. 14 12599–612
[15] Yedrissov A, Khrustalev D, Alekseev A, Khrustaleva A and
Vetrova A 2022 Mater. Today: Proc. 49 2443–8
[16] Sudheshwar A et al 2023 Flex. Print. Electron. 8 015002
[17] Sudheshwar A, Malinverno N, Hischier R, Nowack B and
Som C 2023 Resour. Conserv. Recycl. 189 106757
[18] Arroyos V, Viitaniemi M L K, Keehn N, Oruganti V,
Saunders W, Strauss K, Iyer V and Nguyen B H 2022 CHI
Conf. on Human Factors in Computing Systems Extended
Abstracts (https://doi.org/10.1145/3491101.3519823)
[19] Baylakoğlu I, Fortier A, Kyeong S, Ambat R,
Conseil-Gudla H, Azarian M H and Pecht M G 2021
e-Prime—Adv. Electr. Eng. Electron. Energy 1 100016
[20] Kovács B, Géczy A, Horváth G, Hajdu I and Gál L 2016
Period. Polytech. Electr. Eng. Comput. Sci. 60 223–31
[21] Farkas C et al 2024 Sustain. Mater. Technol. 40 e00902
[22] Grennerat V et al 2024 2024 18th European Conf. on
Antennas and Propagation (Eucap) (Glasgow, UK) pp 1–5
[23] Isola, FR406 datasheet (available at: www.isola-group.com/
wp-content/uploads/data-sheets/fr406.pdf) (Accessed June
08 2024)
[24] Brânzei M, Plotog I and Pencea I 2013 World Acad. Sci. Eng.
Technol. 7 1787–802
[25] Ardunio Nano Documentation (Accessed January 23 2023)
(available at: https://store.arduino.cc/products/arduinonano)
[26] UniPCB Subtractive technology for double sided board
(Accessed January 23 2024) (available at: https://unipcb.hu/
en/technology.html)
[27] Krammer O 2014 Solder. Surf. Mount Technol. 26 214–22
[28] Gal L, Geczy A and Hajdu I 2017. IEEE-ISSE, (https://doi.org/
10.1109/isse.2017.8000884)
[29] Ste˛plewski W et al 2012 Microelectronic materials and
technologies 1, Koszalin Technical University Monograph
Series—Monograph No. 231
[30] Gal L, Geczy A, Horvath G, Rigler D and Hajdu I 2018
IEEE-ISSE. (https://doi.org/10.1109/isse.2018.8443956)
[31] Gandova V, Teneva O, Petkova Z, Iliev I and Stoyanova A
2023 Appl. Sci. 13 10141
[32] Litauszki K, Gere D, Czigany T and Kmetty Á 2023 Sustain.
Mater. Technol. 35 e00527
12