Study on 3D printing of flexible liquid metal circuits with encapsulation on a polyimide substrate

doi:10.19491/j.issn.1001-9278.2025.12.011

Abstract

Abstract:

This study presents a novel 3D printing technique for fabricating and encapsulating flexible liquid metal circuits on a polyimide （PI） substrate. The method precisely controls the circuit's settlement， a key factor in performance， by modulating the imidization degree of the PI base layer and the line width of the liquid metal and its encapsulation. The optimal process parameters reduced the circuit settlement rate to a minimum of 8 %. Furthermore， the influence of various printing parameters on the thickness and surface roughness of the PI layer， as well as on the line widths of the circuit and encapsulation， was systematically investigated. Flexible circuits fabricated with this method exhibited exceptional mechanical stability. After 100 bending cycles with diameters from 2 cm to 3.5 cm， the resistance change rate remained below 0.54 %. Similarly， after 100 torsion cycles within a range from 90 ° to 360 °， the resistance change rate was below 0.45 %. To demonstrate practical application， a flexible LED circuit board was successfully fabricated. The device maintained excellent circuit connectivity and stability under repeated bending and torsion， validating the proposed technique's potential for robust flexible electronics.

Key words: polyimide, three?dimensional printing, liquid metal, flexible circuits

CLC Number:

TQ323.7

GUO Hengrui, WANG Fei, BAI Yanjun, BI Jingxin, CHENG Qianshuai, YANG Wenzhao, WANG Wenzhuo. Study on 3D printing of flexible liquid metal circuits with encapsulation on a polyimide substrate[J]. China Plastics, 2025, 39(12): 64-71.

Figures/Tables 18

Fig.1. Flexible circuit sample preparation process

Fig.2. Material direct writing printing principle

Fig.3. Printing principle of electrohydrodynamic injection

Fig.4. Sedimentation leakage process of the circuit under surface package and the cross section morphology of the circuit after heat curing

Fig.5. The sedimentation process of the circuit in wire package and the cross section morphology of the circuit after heat curing

Fig.6. Comparison before and after circuit settlement

Fig.7. Influence of process parameters on circuit settlement rate

Fig.8. Influence of process parameters on the thickness of PI base layer

Fig.9. Film formation principle of liquid PI base layer

Fig.10. Influence of printing cycle on surface roughness of PI base layer

Fig.11. Influence of print flow on surface roughness of PI base

Fig.12. Influence of process parameters on circuit width

Fig.13. Influence of process parameters on line width of package layer

Fig.14. Bending cycle test principle

Fig.15. Resistance change rate of flexible circuit under different bending states

Fig.16. Principle of torsional loop test

Fig.17. Resistance change rate of flexible circuit under different torsion states

Fig.18. PI⁃based flexible LED circuit board

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