I. Abstract of the Paper’s Core Research

This study custom‑designed and integrated an aerosol jet printing system equipped with an on‑line heating module to regulate the solvent evaporation dynamics of airborne droplets. The system was evaluated under two nozzle operating conditions—room temperature (30°C) and 80°C—focusing on variations in line width, thickness, aspect ratio, and batch-to-batch stability. Covering three mainstream functional inks—silver nanoparticle, conductive carbon, and polyimide—the system enabled multi‑scenario validation, including high‑precision planar circuits, 2.5D micro‑pillars, and conformal curved‑surface circuits. The key research findings are as follows:

Core Mechanism Regulating Online Droplet Evaporation

Unlike conventional substrate‑heating and ink‑can preheating approaches, this design incorporates an aluminum heat‑exchange module within the printhead’s airflow channel, enabling controlled solvent evaporation during aerosol droplet flight. This significantly reduces the liquid‑phase volume of deposited droplets, thereby suppressing spreading and overflow at the source. Leveraging Raoult’s law and the Antoine equation, a theoretical model of multi‑solvent evaporation equilibrium is established, allowing precise prediction of residual liquid‑phase volumes across a range of temperatures.

The contradiction between production capacity and precision has been completely resolved.

Under room-temperature conditions, the linewidth exhibits a sensitivity to deposition rate as high as 1.14 μm⁻¹; upon heating to 80°C, this sensitivity drops to 0.13 μm⁻¹, representing a reduction of approximately 90%. With a tenfold increase in deposition rate, the line width expands by only 27%, whereas conventional unheated equipment under the same conditions shows a fourfold increase in linewidth—balancing high throughput with micrometer‑scale printing accuracy.

All-round improvement in printing performance

Under identical process conditions, the aspect ratio of the lines increased from 0.0025 to 0.29; the standard deviation of line width across multiple sample sets was significantly reduced, markedly improving batch-to-batch consistency; the adhesion and resistivity of the silver lines remained unchanged, and thermal cycling did not degrade the material’s electrical or mechanical properties.

Universal compatibility across all ink systems

The three differentiated solvent systems—organometallic silver paste, polar carbon ink, and water-based polyimide—can all be compatible with online heating processes. With only minor adjustments to the nozzle temperature, there is no need to reformulate the ink, thereby shortening the new-material development cycle.

Breakthrough in Molding of Complex Substrates

When printing on inclined, rough curved surfaces and 2.5D three-dimensional micro‑pillar structures, room‑temperature processes result in distorted lines and blurred outlines. In‑process heating at 80°C suppresses asymmetric spreading, yielding well‑defined pillar edges and uniform heights, thereby expanding the capabilities of AJP‑based 3D manufacturing.

II. Complete Process Flow for Online Heating Aerosol Preparation

Ink Formulation: Silver nano‑organic ink, C45 carbon conductive ink, and water‑based polyimide dielectric ink were prepared separately.

Equipment Modification: The aerosol printhead is equipped with an embedded aluminum heater and a K-type thermocouple–PID temperature control module, while the airflow channel is thermally isolated from the optical components.

Nebulization parameters are fixed: Ultrasonic atomization, with a constant carrier‑gas/ sheath‑gas ratio, and the nozzle temperature varied in 30–80°C intervals for stepwise experiments;

Print by scenario: ① Planar micrometer-scale circuits; ② 2.5D vertical micro-pillar arrays; ③ SLA‑fabricated irregularly shaped rough curved‑surface circuits;

Post-curing: Silver trace: 250°C; carbon ink: 350°C; polyimide: stepwise high-temperature baking.

Characterization: Optical profilometry for measuring line width and thickness, four-point probe measurements of resistivity, tape‑peel adhesion testing, and SEM imaging of surface morphology.

III. Five Core Process Advantages of Online Heating in AJP (Compared with Conventional Room-Temperature or Substrate-Heating Methods)

Production precision is no longer a trade-off; it’s now compatible with industrial production lines.

Under high-speed deposition, droplet spreading is suppressed, enabling fine lines to be maintained even at tenfold faster speeds, thereby addressing the industry’s longstanding challenge of limited lab‑scale viability and rapid obsolescence when scaling up for mass production.

Significantly lowers the barrier to process tuning and offers broader ink compatibility.

There is no need to repeatedly optimize solvent ratios or gas‑to‑ink ratios; a single system can handle all types of inks—water‑based, oil‑based, conductive, and dielectric—shortening the new‑material R&D cycle.

Complex curved surfaces and stable forming of 2.5D three-dimensional structures

Substrate heating cannot be applied to thermally insulating shaped components, while in-line droplet pre-drying is unaffected by substrate material or temperature, and the inclined interface exhibits no streaking distortion.

Batch consistency has improved significantly, and yield has increased substantially.

When the print rate fluctuates slightly, the line width changes very little, eliminating the issue of lines suddenly becoming thicker or thinner at start/stop points and corner transitions, thereby reducing rework costs.

Hardware upgrades are straightforward; existing equipment can be directly upgraded.

Simply add a heating‑temperature‑control module—no need to replace the atomization or gas‑path core components—resulting in low retrofit costs and facilitating batch‑level upgrades on the production line.

IV. Five Core Technological Innovations of This Study

Innovation 1: In-situ Pre-Drying Control Scheme for Flying Droplets

The system validates an on‑line heating mechanism for the print head, which, unlike post‑drying methods such as substrate or ink preheating, precisely controls solvent evaporation prior to impact with the substrate, thereby eliminating spreading defects at the source of the fluid.

Innovation 2: A Theoretical Model of Multi-Solvent Evaporation Equilibrium

By integrating Antoine’s vapor pressure equation, a computational framework for aerosol multi-component droplet–vapor equilibrium has been established, enabling quantitative prediction of the residual liquid-phase fraction at various temperatures and providing theoretical support for parameter standardization.

Innovation 3: A Quantitative Optimization Framework for Deposition Rate Sensitivity

Quantitative analysis demonstrates that, under 80°C operating conditions, the resolution’s sensitivity to flow velocity decreases by 90%. A standard temperature window is established that balances production throughput with measurement accuracy, resulting in a reusable, mass‑production‑ready process specification.

Innovation: A Universal Heating Process for Multi-Material Inks

It covers the three mainstream ink categories—non-polar organic, polar solvents, and water-based—inks, breaking the limitations of single-material processes and enabling a single temperature-control solution to be applied across both conductive and dielectric device manufacturing.

Innovative 5-2.5D Integrated Printing Process for Stereoscopic, Conformal Curved Surfaces

Overcoming the longstanding challenges of material overflow and image blurring on rough, tilted substrates in conventional AJP, we have enabled the stable fabrication of high aspect‑ratio microcolumns and custom‑shaped encapsulation circuits, thereby expanding the frontiers of 3D aerosol‑based applications.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Increasing printing speed inevitably leads to droplet spreading, causing a sharp decline in line‑width accuracy.

✅ Online heating pre-evaporates most of the solvent, sharply reducing the liquid-phase volume of the deposited droplets and significantly suppressing lateral spreading, thereby enabling high-speed printing while maintaining narrow line widths.

Challenge 2: The equipment is highly sensitive to ink and pneumatic parameters, resulting in lengthy adjustment cycles for new materials.

✅ Heating offers independent control, relaxing constraints on ink solvent formulation and eliminating the need for repeated adjustments to the focus ratio and carrier gas flow rate.

Challenge 3: Substrate heating is only suitable for thermally conductive, planar films; it fails on curved or thermally insulating substrates.

✅ The droplets undergo preliminary drying within the airflow channel, independent of the substrate temperature and thermal conductivity, enabling stable printing of parts with any complex geometry.

Challenge 4: Printing start/stop and speed fluctuations at corners lead to uneven line thickness and batch-to-batch variation.

✅ Resolution‑related sensitivity to flow velocity is significantly reduced, dimensional deviations caused by motion‑induced speed variations are markedly minimized, and production‑run consistency is improved.

Challenge 5: Conventional fabrication techniques struggle to produce high-aspect-ratio 2.5D microstructures, resulting in collapsed and blurred pillar edges.

✅ The pre-dried droplets exhibit higher viscosity upon landing, ensuring strong contour retention after patterning; the vertical microcolumns remain well‑aligned without collapse, with sharp edges.

VI. Future Diversified Industrial Application Scenarios

1 In-vehicle / Aeronautical Irregular Curved-Surface RF Antenna

Arc-shaped conformal conductive traces on the housing, with high-speed mass production and no flash, suitable for the batch manufacturing of lightweight communication modules.

2 MEMS micro 2.5D sensing microelectrode array

High-aspect-ratio conductive microcolumns and high-density microstructures for electrochemical and pressure sensors can be fabricated rapidly.

3 Precision Gate Wiring for Flexible Displays

High-speed, high-volume micron-scale circuitry that balances throughput and yield, compatible with large‑format printed electronics production lines.

4 Chip-level packaging with multilayer dielectric interconnects

Precision patterning of polyimide insulating layers and additive manufacturing of integrated multilayer heterogeneous circuits.

5 High-Throughput R&D Platform of the New Materials Laboratory

One-click switching between silver, carbon, and dielectric inks—no need to re‑optimize the equipment—enables rapid batch prototyping.

Image and Text Guide

Figure 1. In-line heating device for aerosol jet printing and preliminary validation

Figure 2. Effect of in-line heating on AgNP printing (12 sccm CGFR, focus ratio 5)

Figure 3. In‑line heating enables both high‑throughput and high‑resolution printing (a–c: high throughput; d–f: high resolution).

Figure 4. Online heating is extended to various ink systems, accelerating materials development.

Figure 5. Conformal Printing and High Aspect Ratio (2.5D) Printing