Advances in printed flexible and stretchable circuits have enabled transformative applications in wearable electronics, soft robotics, and biomedical devices. Unlike conventional rigid electronics, these circuits conform to dynamic surfaces, withstand mechanical deformation, and integrate seamlessly with human tissues. Key manufacturing techniques include inkjet printing, screen printing, and 3D printing, each offering distinct advantages in resolution, material compatibility, and scalability. Conductive inks, dielectric materials, and substrate choices play critical roles in performance, while resolution and durability challenges persist. Comparisons with traditional lithography highlight trade-offs in precision versus flexibility and cost-effectiveness for mass production.

Inkjet printing has emerged as a versatile method for depositing functional materials onto flexible substrates with high precision. This non-contact technique employs piezoelectric or thermal actuators to eject droplets of conductive or dielectric inks, enabling rapid prototyping and customization. Silver nanoparticle inks dominate due to their high conductivity and stability, though copper and carbon-based alternatives are gaining traction for cost reduction. Challenges include nozzle clogging, droplet spreading on elastomeric substrates, and the need for post-processing sintering. Recent advancements in substrate surface modification and low-temperature sintering have improved adhesion and conductivity while preserving stretchability. Multi-material inkjet systems now enable simultaneous deposition of conductors, semiconductors, and insulators, facilitating monolithic integration of circuits.

Screen printing remains the workhorse for high-throughput manufacturing of stretchable electronics. This method uses a mesh stencil to transfer viscous inks onto substrates, making it suitable for large-area patterning with feature sizes down to 50 micrometers. Thick-film conductive pastes containing silver flakes or carbon fillers provide robust electrical pathways, while stretchable binders like polyurethane or silicone ensure mechanical compliance. Hybrid approaches combine screen-printed interconnects with mounted components, achieving stretchability through engineered serpentine geometries or buckling architectures. Limitations include difficulty in printing high-resolution multilayered structures and material waste during screen preparation. Innovations in dynamic stencil designs and roll-to-roll compatible screens address these issues, enhancing throughput for wearable sensor arrays and epidermal electronics.

3D printing techniques such as direct ink writing and aerosol jet printing enable conformal fabrication of stretchable circuits on complex surfaces. These additive methods extrude functional inks through microscale nozzles, building structures layer-by-layer with precise control over geometry. Elastomeric substrates like polydimethylsiloxane (PDMS) or thermoplastic polyurethane (TPU) serve as printable matrices, often combined with embedded conductive traces. Challenges include maintaining electrical continuity during stretching and achieving sufficient vertical resolution for multilayer devices. Recent developments in shear-thinning conductive hydrogels and self-healing elastomers have expanded the capabilities of 3D-printed stretchable circuits, particularly for implantable medical devices requiring biocompatibility.

Conductive inks for flexible circuits must balance electrical performance with mechanical resilience. Particle-based inks rely on metallic fillers (silver, gold, or copper) or carbon nanomaterials (graphene, carbon nanotubes) dispersed in polymer matrices. Percolation thresholds and filler alignment influence conductivity under strain, with optimized formulations achieving less than 10% resistance change at 50% elongation. Intrinsically conductive polymers like PEDOT:PSS offer transparency and flexibility but suffer from lower conductivity. Liquid metal alloys such as eutectic gallium-indium (EGaIn) enable ultra-stretchable interconnects due to their fluidic nature, though oxidation and containment remain hurdles. Dielectric materials like UV-curable acrylates or silicone elastomers provide insulation between layers, with permittivity and loss tangent tailored for high-frequency operation.

Resolution limitations stem from ink rheology, substrate interactions, and printer capabilities. Inkjet systems achieve 20-50 micrometer features, while electrohydrodynamic printing pushes this below 1 micrometer at the cost of speed. Screen printing typically delivers 50-100 micrometer lines, whereas 3D printing resolutions vary from 10 micrometers to several hundred micrometers depending on nozzle size. Achieving fine-pitch interconnects on stretchable substrates requires compensation for distortion during deformation, often addressed through computational modeling of strain distributions. Emerging techniques like laser-induced forward transfer and nanoimprint lithography bridge the gap between conventional printing and photolithography, offering sub-micrometer resolution with compatibility for elastomeric materials.

Scalability for mass production favors roll-to-roll compatible processes such as gravure printing or flexography, which combine high speed with moderate resolution. These methods have been adapted for stretchable electronics by integrating inline curing stages and tension control systems to handle compliant substrates. Hybrid manufacturing approaches leverage printed interconnects alongside pick-and-place assembly of rigid components, balancing performance with mechanical flexibility. Cost analyses indicate that printed stretchable circuits become economically viable at production volumes exceeding 10,000 units, with significant savings in material usage compared to subtractive lithography.

Traditional lithography offers superior resolution and reliability but struggles with flexible and stretchable formats. Photolithography on polyimide achieves micrometer-scale features but requires complex transfer processes to elastomers, often compromising adhesion. Laser ablation provides an alternative for patterning thin metal films on stretchable substrates, though it lacks the material diversity of printing. Printed electronics excel in reducing material waste, enabling customization, and accommodating large-area formats unsuitable for cleanroom processes. The absence of vacuum deposition and etching steps in printing reduces energy consumption and capital costs, particularly for disposable or short-lifetime applications.

Durability testing reveals that printed stretchable circuits withstand thousands of bending cycles with minimal performance degradation when properly designed. Encapsulation layers of silicone or polyurethane protect against moisture and abrasion, extending operational lifetimes in harsh environments. Accelerated aging tests simulate years of use under mechanical stress, guiding material selection for specific applications. Emerging standards for reliability metrics facilitate adoption in medical and automotive sectors where failure carries significant consequences.

Future directions focus on improving print resolution without sacrificing throughput, developing eco-friendly conductive inks, and enhancing interoperability with conventional electronics. Machine learning optimizes print parameters for novel material combinations, while self-alignment techniques reduce post-processing steps. Integration of energy harvesting elements like printed piezoelectrics or solar cells enables autonomous operation of stretchable systems. As manufacturing maturity increases, printed flexible and stretchable circuits will transition from lab-scale curiosities to mainstream production, unlocking new possibilities in human-machine interfaces and soft robotics.