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Recyclable vitrimer-based printed circuit boards for sustainable electronics

Nature Sustainability (2024)Cite this article

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Abstract

Printed circuit boards (PCBs) are ubiquitous in electronics and make up a substantial fraction of environmentally hazardous electronic waste when devices reach end-of-life. Their recycling is challenging due to their use of irreversibly cured thermoset epoxies in manufacturing. Here, to tackle this challenge, we present a PCB formulation using transesterification vitrimers (vPCBs) and an end-to-end fabrication process compatible with standard manufacturing ecosystems. Our cradle-to-cradle life-cycle assessment shows substantial environmental impact reduction of the vPCBs over conventional PCBs in 11 categories. We successfully manufactured functional prototypes of Internet of Things devices transmitting 2.4 GHz radio signals on vPCBs with electrical and mechanical properties meeting industry standards. Fractures and holes in vPCBs are repairable while retaining comparable performance over multiple repair cycles. We further demonstrate a non-destructive recycling process based on polymer swelling with small-molecule solvents. Unlike traditional solvolysis recycling, this swelling process does not degrade the materials. Through dynamic mechanical analysis, we find negligible catalyst loss, minimal changes in storage modulus and equivalent polymer backbone composition across multiple recycling cycles. This recycling process achieves 98% polymer recovery, 100% fibre recovery and 91% solvent recovery to create new vPCBs without performance degradation. Overall, this work paves the way for sustainability transitions in the electronics industry.

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Fig. 1: Transesterification vitrimer-based fully recyclable PCB.
Fig. 2: Glass fibre-reinforced vitrimer composite.
Fig. 3: Characterization of vPCB.
Fig. 4: Platform evaluation.
Fig. 5: Repair and remanufacturing of vPCB.
Fig. 6: Recycling of vPCB.

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Data availability

All data needed to evaluate the conclusions of this study are available in the paper or in the Extended Data and Supplementary Information. Source data are provided with this paper.

Code availability

The source code is available for download on GitHub at https://github.com/iamZhihanZhang/vPCB-IoT-Platform.git.

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Acknowledgements

We thank T. Cheng for discussion, Z. Englhardt for help with Bluetooth coding, B. Kuykendall for the use of mechanical testers, C. Li for feedback on the figures, K. Liao and M. Parker for help with flammability testing, and H. Wang for help with composite fabrication. We also thank D. Baker, F. Newman and C. Toskey for help with sputter coating and copper plating. This research was supported by the Microsoft Climate Research Initiative, an Amazon Research Award and the Google Research Scholar Program. Z. Zhang was supported by the University of Washington CEI Fellowship.

Author information

Authors and Affiliations

  1. Paul G. Allen School of Computer Science and Engineering, University of Washington, Seattle, WA, USA

    Zhihan Zhang, Jake A. Smith, Bichlien H. Nguyen, Shwetak Patel & Vikram Iyer

  2. Department of Mechanical Engineering, University of Washington, Seattle, WA, USA

    Agni K. Biswal, Ankush Nandi & Aniruddh Vashisth

  3. Microsoft Research, Redmond, WA, USA

    Kali Frost, Jake A. Smith & Bichlien H. Nguyen

  4. Department of Electrical and Computer Engineering, University of Washington, Seattle, WA, USA

    Shwetak Patel

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Contributions

Z.Z., B.H.N., A.V. and V.I. conceptualized, organized and structured the work. Z.Z., A.K.B. and A.N. fabricated GFRV composites. Z.Z. manufactured vitrimer-based PCB and conducted characterizations. Z.Z. designed the hardware system, experiments and evaluations. Z.Z., J.A.S. and B.H.N. designed the repair experiments and evaluations. Z.Z., A.K.B., J.A.S., B.H.N. and A.V. designed the recycling experiments and evaluations. Z.Z. and A.K.B. conducted material characterizations. K.F. conducted the life-cycle assessment analysis. Z.Z. and V.I. wrote the manuscript. S.P., A.V. and V.I. jointly supervised the work. All authors contributed to the study concept and experimental methods, discussed the results and edited the manuscript.

Corresponding authors

Correspondence to Aniruddh Vashisth or Vikram Iyer.

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Competing interests

K.F., J.A.S. and B.H.N. are employees of Microsoft Corporation. S.P. is an employee of Google LLC. Z.Z., A.K.B., A.N., A.V. and V.I. declare no competing interests.

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Nature Sustainability thanks Rasoul Nekouei, Bozhi Tian, Xianlai Zeng and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Dynamic mechanical analysis of pristine and recycled vitrimer.

a, b, c, Normalized stress relaxation curves of pristine vitrimer (a), vitrimer after one recycling cycle (b), and vitrimer after two recycling cycles (c) at temperatures ranging from 140 °C to 240 °C. In all cases increasing temperature results in faster stress relaxation. d, e, f, Characterized storage modulus, loss modulus, and tan delta of pristine vitrimer (d), vitrimer after one recycling cycle (e), and vitrimer after two recycling cycles (f).

Extended Data Fig. 2 Peel strength for copper-clad laminates with a layer of partially cured vitrimer.

a, b, Curves of the peeling force per width of copper-clad versus displacement for laminates with a layer of partially cured vitrimer after thermal stress (a), and at 125 °C (b) compared to the PCB standard of FR-4.

Source data

Extended Data Fig. 3 Joint strength of repaired via holes in vPCB.

a, Photograph showing the joint strength testing setup. Specimen is centered on a metal hollow cylinder support with a support span of 16 mm. b, Characterized shear stress of repaired via holes in GFRV compared to the repaired holes in FR-4 using super glue. c, Photograph of FR-4 after shear punch, showing cyanoacrylate glue bond broke. d, Photograph of GFRV after shear punch, showing the repaired via hole was deformed into a funnel-shape under the force of punch but remained intact, indicating a stronger interface at the hole boundary.

Extended Data Fig. 4 Solvents test for vPCB recycling.

GFRV samples were cut into rectangular shapes and immersed in various solutions (Acetone, CHCl3, DMF, THF); the top, middle and bottom photos were taken immediately after immersing, after 48 h, and after 96 h, respectively.

Extended Data Fig. 5 Characterized storage modulus, tan delta, retention of storage modulus, and vitrimer transition temperature of recycled vitrimer.

a, Characterized storage modulus temperature sweep results of vitrimer after one and two recycling cycles compared to pristine. The storage modulus shows a slight decrease after recycling. b, Tan delta temperature sweep results of vitrimer after one and two recycling cycles compared to pristine, tan delta broadens and the left shift of peaks is negligible after recycling. c, Retention of storage modulus of vitrimer after one and two recycling cycles compared to pristine, data is presented as mean (SD) of vitrimer specimen in 4 parallel experiments (N = 4). d, Tv comparison of pristine vitrimer, vitrimer after one and two recycling cycles, indicating the shift of Tv is negligible after recycling. The Arrhenius plot is derived with a linear fit to the low-temperature region (140 °C to 180 °C), and its intersection with where the stress-relaxation constant is 10^6 indicates the Tv.

Source data

Extended Data Fig. 6 Characterized electrical and mechanical properties of reformed vPCB.

a, b, c, Characterized dielectric constant (a), flexural strength (b), volume resistivity (c), and loss tangent (d) of reformed GFRV compared to virgin composite, data is presented as mean (SD) of 3 vPCB specimens in 1 (a, d) and 1000 (c) measurements (N = 3, 1000, and 3 for dielectric constant, resistivity, and loss tangent, respectively).

Source data

Extended Data Fig. 7 Environmental impact of vPCB freight.

Comparison of the environmental impact of vPCB freight versus conventional FR-4 prepreg freight across 11 different categories.

Source data

Extended Data Fig. 8 Breakdown of global warming potential for conventional FR-4 PCB.

Global warming potential impact breakdown of conventional FR-4 PCB, showing that raw materials account for 48.5% of the total impact.

Source data

Supplementary information

Supplementary Information

Supplementary Discussions, Figs. 1–11, Table 1 and References.

Reporting Summary

Supplementary Video 1

Vitrimer swelling in THF. Time-lapse video showing the swelling process of the vitrimer matrix in THF at room temperature.

Supplementary Video 2

Flammability test for GFRV composite. Video showing a GFRV composite being ignited, burning and extinguished.

Source data

Source Data Fig. 2

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Source Data Extended Data Fig. 2

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Source Data Extended Data Fig. 7

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Source Data Extended Data Fig. 8

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Zhang, Z., Biswal, A.K., Nandi, A. et al. Recyclable vitrimer-based printed circuit boards for sustainable electronics. Nat Sustain (2024). https://doi.org/10.1038/s41893-024-01333-7

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