I. Core Research Summary

• Low-Temperature Laser Sintering for Protecting Heat-Sensitive Substrates

The substrate deformation temperature is only 52–54°C; high‑temperature sintering in an oven is abandoned, and instead, a 300 mW infrared spot laser is used for localized heating. Only the silver layer is heated, with no warping or delamination of the substrate, and the adhesion of the sintered silver film reaches the highest AST 5B rating. The as‑sintered silver film has a thickness of approximately 550–900 nm and a resistivity of 63 μΩ·m, which is 360 times that of pure copper.

• Precise control of plating duration enables precise regulation of copper film thickness and electrical conductivity.

Under a constant 2 mA current, the copper deposition rate exhibits steady, linear growth; after just 5 minutes of electroplating, the resistivity decreases by more than a factor of 30. Extending the plating time to 8 minutes yields a copper layer approximately 900 nm thick, with the film’s pores completely filled and the conductive pathways becoming dense and continuous.

• Excellent interfacial adhesion; controlled electroplating exhibits no large‑area delamination.

During electroplating, the grid‑tape adhesion test maintains a 5B rating for up to 8 minutes; beyond 8 minutes, internal stresses in the coating surge, leading to delamination and peeling, thereby defining a clear safe electroplating process window. FIB cross‑sectional analysis combined with EDS characterization confirms that copper fully penetrates the silver pores, with tight interfacial bonding between copper and silver.

• Achieve standard industrial SMT soldering capabilities.

Unplated porous silver‑film solder exhibits poor wetting and leads are prone to damage; in contrast, copper‑plated traces feature a smooth, even surface, and molybdenum‑alloy pads achieve an average shear strength exceeding 1000 g, fully meeting the MIL‑STD‑883 military‑grade soldering reliability standard.

• High-precision selective metallization process

Copper is deposited only in the aerosol‑printing area, with no metal deposition on the bare substrate; a photoresist solder mask is unnecessary. Complex micron‑scale RF and sensor circuits can be selectively thickened, balancing pattern fidelity with high electrical conductivity requirements.

II. Complete Process Flow and Core Advantages of the Aerosol–Electroplating Hybrid Technology

(1) Complete Integrated Preparation Process

• Veroclear thermoplastic substrate cleaning pretreatment;
• Optomec AJ300 ultrasonic atomization silver nanoparticle ink, with CNC‑controlled printing of square test pads and fine traces.
• The sample was allowed to dry naturally at room temperature overnight, followed by localized sintering and shaping of a porous silver seed layer using an 830 nm infrared laser grating.
• The sample is bonded with conductive epoxy, and the lead wires are isolated in non-printed areas; the surface is then acid‑etched to activate it.
• In the acidic copper plating bath, electrolytic deposition is carried out at a constant current of 2 mA, with the plating duration controlled in stages.
• Deionized water and hot acetone are used for cleaning, followed by nitrogen purging to dry the surface, thereby completing the high‑conductivity, solderable composite metal interconnect.

(II) Five Core Process Advantages (Comparison with Pure Aerosol and Photolithographic Copper)

• Micron-level high-precision seed layer, with selective electroplating and no pattern distortion.

Aerosols enable stable printing of 10-μm‑wide fine lines; electroplating grows exclusively in the silver‑patterned regions without widening the lines, while photolithography cannot simultaneously fabricate fine patterns on curved surfaces.

• Low-temperature laser sintering compatible with fully thermosensitive flexible substrates.

The entire process avoids high‑temperature ovens; only laser‑localized heating is used to activate the conductive layer, making it suitable for heat‑sensitive substrates such as plastics, 3D‑printing resins, and medical polymers.

• Composite metals combine high precision with bulk-level electrical conductivity.

Aerosols enable fine‑line patterning, while electroplating fills pores and thickens the metal, addressing high‑resistance defects caused by porosity in single‑layer printed circuits and achieving performance that approaches that of standard copper foil used in PCBs.

• Compatible with standard industrial surface-mount soldering, enabling seamless integration into the additive manufacturing mass-production workflow.

Pure silver printing films cannot be processed on SMT lines; after copper plating, they exhibit excellent solder wettability and meet the required shear strength, making them suitable for direct use in high‑volume component placement.

• Low-cost digital iteration, curved-surface conformal metallization

Maskless aerosol rapid patterning; for irregularly shaped and curved substrates, a seed layer is first printed followed by electroplating—traditional full‑substrate plating cannot achieve region‑specific, precise metallization.

III. Five Key Technological Innovations

Innovation 1: A novel composite process combining an aerosol‑silver seed layer with selective electroplating of copper.

Innovative Infrared Local Laser Low-Temperature Sintering Scheme 2

Innovation: Microscopic Conductivity Enhancement Mechanism of Copper-Filled Porous Silver

Innovation 4: A Military-Grade Welding Reliability Solution for Additive Manufacturing Circuits

Innovative General-Purpose Process for Selective Metallization of Five Partitioned Areas

IV. Current Industry Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Pure aerosol silver films have large pores and extremely high resistivity, resulting in significant losses under RF or high-current conditions.

Challenge 2: The substrate materials used in flexible and 3D printing have poor heat resistance, leading to direct deformation during conventional high-temperature sintering.

Challenge 3: The printed silver film has a porous surface, preventing solder from wetting and making SMT component mounting impossible.

Challenge 4: Whole‑piece electroplating can easily lead to edge spreading and loss of precision.

Challenge 5: A single aerosol‑based process cannot simultaneously achieve fine patterning and thick, low‑loss metal layers.

V. Future Diversified Industrial Application Scenarios

• Flexible RF Circuit for Automotive Millimeter-Wave Radar

• Wearable health-monitoring sensor array

• 3D-printed structural embedded electronics

• Military‑grade lightweight RF packaging components

• Rapid PCB Prototyping for University Laboratories

Figure 1. Schematic diagram of the optimized printed interconnect architecture, illustrating: a) the printing process; b) the laser sintering process; and c) the electroplating process. The figure shows post‑printing images of a test sample (7 × 7 mm pads): d) an optical image (scale bar = 1 mm); e) an enlarged view (scale bar = 20 µm). f) An optical image of the test sample after laser sintering and tape testing (scale bar = 1 mm); g) an enlarged view (white arrows indicate discontinuities in the thin film; scale bar = 20 µm). h) Resistivity and thickness distribution across the test sample (n = 12).

Figure 2. Characterization of electrodeposited copper: (a) Variation of copper thickness with electrodeposition time; (b) Variation of resistivity with electrodeposition time (n = 3); and an inset showing the optical image of the sample after 6 minutes of electrodeposition (scale bar = 3 mm).

Figure 3. Adhesion test results for the copper‑plated layer: a) Variation of adhesion values with plating time; b) Adhesion image of the sample plated for 4 minutes; c) Adhesion image of the sample plated for 8 minutes. Scale bar: 1 mm.

Figure 4. a) Scanning electron microscope image of a sintered silver nanoparticle film (scale bar: 5 μm). White markers indicate typical regions of good sintering (upper inset, magnified view; the red dashed box highlights an underlying region with poor sintering, scale bar: 1 μm); red markers denote typical areas of poor sintering (lower inset, magnified view, scale bar: 1 μm). b) Scanning electron microscope image of a copper‑plated film (scale bar: 5 μm; inset, magnified view, scale bar: 1 μm); c) Focused ion beam cross‑sectional image (scale bar: 1 μm). EDS spectra show d) the distribution of copper and e) the distribution of silver (both scale bars: 1 μm). f) Top‑down view of a square molybdenum alloy test specimen mounted on a printed silver nanoparticle film, illustrating post‑sintering damaged regions (white markers) and intact regions (red markers), scale bar: 500 μm; g) The intact condition of a copper‑plated film after mounting the molybdenum alloy test piece (scale bar: 500 μm); h) Oblique cross‑sectional image of the molybdenum alloy test piece mounted on the copper film, clearly revealing the meniscus structure indicated by the white arrow, scale bar: 500 μm.