# In-Mold Electronics with Biosourced and Biodegradable Polymers

Caroline Goument, Tony Gerges, Philippe Lombard, Hayet Lakhdar, Murat Arli, Valernst Martial Gilmus, Simon A. Lambert, Jean-Yves Charmeau, Michel Cabrera, Bruno Allard

► To cite this version:

Caroline Goument, Tony Gerges, Philippe Lombard, Hayet Lakhdar, Murat Arli, et al. In-Mold Electronics with Biosourced and Biodegradable Polymers. LOPEC Conference for Printed Electronics, Feb 2023, München, Germany. , 2023. [https://hal.science/hal-04069869](https://hal.science/hal-04069869)

HAL Id: hal-04069869

https://hal.science/hal-04069869

Submitted on 14 Apr 2023

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## In-Mold Electronics : principle and materials

* In-Mold Electronics (IME) is a 3D plastronic technology combining the plastics processing field with electronics.

<figure><img src="image_1.png" /></figure>

* Process in three main steps:

(a) Screen printing (ink deposition on a polymer film) + electronic components (SMD) pasting

(b) Thermoforming (substrate shaping from 2D to 3D through heating)

(c) Overmolding by injection.

* PolyCarbonate (PC), petroleum-based, reference material in IME

## Polymer substrate characterization

* Polymer of interest: PolyLactic acid (PLA 300 µm)

* Biosourced and biodegradable, for the manufacturing of more sustainable IME devices

PLA1, PLA2: pellets Ingeo 2003D and 3251D from NatureWorks LLC

PC1, PC2: Makrofol DE 1-1 films and pellets 2405 from Covestro

* Applications in signal electronics and HMI (Human-Machine Interface)

<table><thead><tr><th>Properties</th><th>PLA1</th><th>PLA2</th><th>PC1</th><th>PC2</th></tr></thead><tbody><tr><td>Tg (°C)</td><td>55</td><td>59</td><td>150</td><td>144</td></tr><tr><td>Tm (°C)</td><td>151</td><td>171</td><td>/</td><td>/</td></tr><tr><td>Td (°C)</td><td>310</td><td>310</td><td>454</td><td>454</td></tr><tr><td>Elongation at break (%)</td><td>3.9</td><td>/</td><td>128.7</td><td>/</td></tr><tr><td>Impact resistance (kJ/m²)</td><td>/</td><td>1.7 (1J) (notched)</td><td>/</td><td>8.9 (15J) (notched)</td></tr><tr><td>Surface roughness Sa (µm)</td><td>0.37</td><td>/</td><td>0.19</td><td>/</td></tr><tr><td>Surface energy (mN/m)</td><td>38</td><td>46</td><td>46</td><td>47</td></tr></tbody></table>

PLA not thermally and mechanically as good as PC:

* Low Tg (60°C) → necessary to adapt and optimize the process and the choice of application to this limitation.

* Minimal elongation at break (less than 5%) and impact resistance (just 2 kJ/m²) rather unfavorable to IME as such.

Surface roughness minimal and surface energy around 40-45 mN/m: the polymer wettability can influence the adhesion of conductive ink and electronic components in screen printing. → advantageous properties similar to PC.

## Characterization toward an electrical circuit

### Adhesion of ME603 conductive ink

<figure><img src="image_2.png" /></figure>

* Standardized cross-cut test (ISO 2409, scotch test).

* Great adhesion on PLA1 and PC1 substrates
Classification 0 = Edges of the cuts smooth and no squares of the lattice detached.

Drying ME603 and ME902 on PLA1 : 55°C – 2h30

### Adhesion of SMDs

* ME902 conductive paste + ethyl cyanoacrylate

* Shear testing of SMD on ME603 traces

<table><thead><tr><th></th><th>Drying conditions</th><th>Shear stress (N/mm²)</th></tr></thead><tbody><tr><td>ME902 on PC1 (ref)</td><td>120°C – 20 min</td><td>7.68</td></tr><tr><td>ME902 on PC1</td><td>55°C – 2h30</td><td>2.76</td></tr><tr><td>ME902 on PLA1</td><td>55°C – 2h30</td><td>1.80</td></tr><tr><td>ME902 + cyano on PC1</td><td>55°C – 2h30</td><td>8.67</td></tr><tr><td>ME902 + cyano on PLA1</td><td>55°C – 2h30</td><td>9.10</td></tr></tbody></table>

* Fracture surface = in ME902 paste layer

* Adhesion decrease with drying temperature decrease

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

### Resistivity of ME603 ink

* Resistance measurements with four-point probes method and cross-sectional area S with confocal profilometer

<figure><img src="image_5.png" /></figure>

<table><thead><tr><th></th><th>ME603 on PC1<br>(120°C – 20 min)</th><th>ME603 on PLA1<br>(55°C – 2h30)</th></tr></thead><tbody><tr><td>Resistivity<br>(µΩ.cm)</td><td>31 – 54</td><td>290 – 300</td></tr></tbody></table>

* Higher resistivity on PLA1 than on PC1 (55°C vs. 120°C) → Loss in conductivity on PLA1

* Good enough to operate a simple electronic circuit

### Proof of concept

<figure><img src="image_6.png" /></figure>

NE555 IC timer
3 resistors
1 capacitor
1 LED

<figure><img src="image_7.png" /><figcaption>After screen printing + SMD pasting</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>After thermoforming</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>After overmolding by injection</figcaption></figure>

### Conclusion

* The feasibility of IME on PLA was demonstrated:

* ✓ The electronic circuit is well encapsulated

* ✓ The performances of the conductive ink is sufficient for our applications (signal electronics) and the ink and SMD adhesion is excellent

* ✓ The mechanical properties of the proof of concept in PLA remain interesting

* ✓ The ink conductivity can be improved → photonic curing

* C. Goument et al. In-Mold Electronics on Poly(Lactic Acid): towards a more sustainable mass production of plastronic devices. *Int J Adv Manuf Technol* (2023). https://doi.org/10.1007/s00170-023-10878-4

### Acknowledgements

This work has been financially supported by the Auvergne-Rhône-Alpes Region, BioAntenna project (Antenne pour IoT sur polymère biodégradable pour le stockage et la récupération d'énergie) of the Pack Ambition Recherche 2020 (Convention no. 20 009551 01-22464) that we gratefully acknowledge.

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Laboratoire Ampère

UMR CNRS 5005

Génie Électrique, Automatique, Bioingénierie

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UNIVERSITÉ
DE LYON

INSA

INSTITUT NATIONAL
DES SCIENCES
APPLIQUÉES

LYON

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ÉCOLE
CENTRALE LYON

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Lyon 1