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IEC/IEEE 62659: Nanomanufacturing — Nano Ink Jet Printing
Standard for the fabrication, characterization, and quality assessment of nano ink jet printing processes in nanomanufacturing
IEC/IEEE 62659, published in 2015 as a dual-logo standard developed jointly by IEC Technical Committee 113 and IEEE Nanotechnology Council, defines the standard for nano ink jet printing as a nanomanufacturing process. This landmark standard addresses the growing need for standardized terminology, process characterization methods, and quality assessment protocols in the rapidly evolving field of nano ink jet printing. Unlike conventional ink jet printing, which deals with micrometre-scale features, nano ink jet printing involves the controlled deposition of functional nanomaterials — including conductive nanoparticles, quantum dots, carbon nanotubes, graphene, and biologically active compounds — onto substrates to create functional devices and structures at the nanoscale. Applications span printed electronics (RFID antennas, sensors, thin-film transistors), biomedical devices (biosensors, drug delivery matrices), optical components (photonic crystals, microlens arrays), and energy devices (organic photovoltaic cells, battery electrodes, fuel cell catalysts).
IEC/IEEE 62659 covers both continuous ink jet (CIJ) and drop-on-demand (DOD) printing methods as applied to nano-functional inks. The standard addresses the entire process chain from ink formulation through droplet generation, deposition, post-processing, and final device characterization. It applies to printing processes using inks containing nanoparticles, nano-emulsions, or molecular precursor solutions that result in nano-structured features after deposition and post-processing.
Nanoink Formulation and Droplet Formation
The standard establishes comprehensive requirements for nanoink characterization. Key parameters include nanoparticle size distribution (D10, D50, D90, and span), particle morphology (sphericity, aspect ratio, agglomeration state), surface charge (zeta potential, minimum +/- 30 mV for colloidal stability), solids loading (weight percent of functional material), viscosity (typically 2-20 mPa.s for DOD printing, 2-10 mPa.s for CIJ), surface tension (25-35 mN/m for aqueous inks, 20-30 mN/m for solvent-based inks), and evaporation rate. The ink must remain stable against sedimentation and agglomeration for a minimum of 30 days under storage conditions and must pass a printhead compatibility test demonstrating no clogging after 60 minutes of continuous printing with 10-minute idle intervals.
Droplet formation dynamics are critical to print quality. The standard defines key jetting parameters: droplet velocity (typically 5-10 m/s for DOD), droplet volume (from sub-picolitre to tens of picolitres, depending on nozzle diameter), satellite drop formation (must be less than 5% of primary droplet volume), and jetting frequency (up to 100 kHz for industrial printheads). The Ohnesorge number (Oh = eta / sqrt(rho . sigma . d), where eta is viscosity, rho is density, sigma is surface tension, and d is nozzle diameter) must lie within the printable range of 0.1 to 1.0 for stable droplet formation. For nano-inks specifically, the standard requires that the nanoparticle size be less than 1/50th of the nozzle diameter to prevent clogging, and that agglomerates larger than 1/20th of the nozzle diameter be removed by filtration prior to printing.
| Parameter | DOD Printing | CIJ Printing | Test Method |
|---|---|---|---|
| Viscosity (mPa.s) | 2 – 20 | 2 – 10 | Rotational rheometry |
| Surface tension (mN/m) | 25 – 35 (aqueous); 20 – 30 (solvent) | 25 – 40 | Wilhelmy plate / pendant drop |
| Nanoparticle size | < 1/50 nozzle diameter | < 1/50 nozzle diameter | DLS or SEM/TEM |
| Zeta potential (mV) | < -30 or > +30 | < -30 or > +30 | Electrophoretic light scattering |
| Solids loading (wt%) | 0.1 – 40 | 0.1 – 20 | TGA |
| Ohnesorge number | 0.1 – 1.0 | 0.1 – 1.0 | Calculated from properties |
| Sedimentation stability | >= 30 days | >= 30 days | Lumisizer / Turbiscan |
A critical failure mode in nano ink jet printing is nozzle clogging caused by nanoparticle agglomeration or solvent evaporation at the nozzle orifice. The standard requires that the ink formulation include humectants to control evaporation at the nozzle meniscus and that the printhead incorporate a non-contact nozzle cleaning cycle (purge + spit + wipe) at intervals not exceeding 10 minutes of idle time. For production environments, printhead maintenance schedules must be validated through continuous printing trials of at least 8 hours duration without catastrophic nozzle failure.
Process Control and Printed Feature Characterization
The standard specifies process monitoring and control requirements for nano ink jet printing systems. Critical process parameters that must be monitored in real time include nozzle temperature (controlled to +/- 1 deg C), substrate temperature (typically 30-60 deg C for solvent evaporation control, up to 200 deg C for reactive inks), printhead-to-substrate distance (maintained within +/- 50 micrometres), ambient humidity (controlled to 40-60% RH for aqueous inks), and droplet volume consistency (coefficient of variation across all nozzles < 3%). Drop watcher camera systems are recommended for continuous droplet visualization, with automated jetting parameter adjustment to maintain consistent droplet characteristics throughout the print run.
Characterization of printed nano-features is a major contribution of the standard. The printed feature dimensions must be measured using optical microscopy (for features > 10 micrometres), scanning electron microscopy (for features 100 nm to 10 micrometres), or atomic force microscopy (for sub-100 nm features). The standard defines line edge roughness (LER) requirements: for printed conductive traces, the LER must be less than 10% of the line width for features below 50 micrometres and less than 5% for features above 50 micrometres. Printed film thickness uniformity must be within +/- 10% of the target value across a 100 mm x 100 mm print area. Electrical characterization of printed conductive features requires four-point probe measurement of sheet resistance, with the resistivity reported as a multiple of bulk material resistivity — typical values for printed silver nanoparticle traces after sintering range from 3x to 10x bulk silver resistivity (0.015 to 0.050 Ohm.micrometre), depending on sintering conditions and nanoparticle loading.
The post-processing step — typically thermal sintering, photonic curing, or chemical sintering — is the most critical factor determining final printed feature performance. For printed silver nanoparticle conductors, the standard specifies that sintering at 150 deg C for 30 minutes should achieve at least 30% of bulk silver conductivity. Photonic curing using intense pulsed light can achieve equivalent conductivity in milliseconds at room temperature, enabling printing on heat-sensitive substrates such as PET and paper that cannot withstand conventional thermal sintering at 120-200 deg C for extended periods.
Engineering Design Insights for Nano Ink Jet Manufacturing
When scaling nano ink jet printing from laboratory development to production manufacturing, several engineering challenges must be addressed. First, substrate management and handling are critical. The standard requires that substrate flatness be maintained within +/- 10 micrometres across the print area, and that the substrate be secured to the print platen using vacuum or electrostatic clamping to prevent movement during printing. For flexible substrates, web tension must be controlled to +/- 2 N/m to maintain dimensional stability, and the substrate must be conditioned to the printing environment temperature and humidity for at least 2 hours before printing to prevent dimensional changes during the printing process.
Second, multi-pass printing for increased layer thickness or material composition gradients requires precise layer-to-layer registration. The standard specifies that alignment accuracy between successive printed layers must be better than +/- 5 micrometres for 3-sigma, achieved through fiducial mark recognition and closed-loop substrate positioning with linear encoders. For printed electronics applications requiring multiple materials (conductors, dielectrics, semiconductors), the standard recommends that the printing order account for surface energy compatibility and that each layer be dried or partially cured before depositing the subsequent layer to prevent intermixing.
Third, quality assurance in production requires statistical process control based on in-line metrology. The standard recommends automated optical inspection after each functional layer, measuring feature dimensions, layer thickness, and defect density (pinholes, edge roughness, missing features). The acceptance criteria must be defined from the device functional requirements: for example, a printed RFID antenna may require line width within +/- 10% and sheet resistance within +/- 20% of target, while a printed sensor electrode may require more stringent dimensional tolerance but relaxed electrical tolerance. Statistical sampling plans should follow ISO 2859 or equivalent, with defect accounting and root cause analysis for any out-of-specification condition.
| Feature Type | Characteristic | Typical Specification | Measurement Method |
|---|---|---|---|
| Conductive traces | Line width accuracy | +/- 10% of target | Optical microscopy |
| Conductive traces | Line edge roughness | < 10% of line width | SEM / profilometry |
| Printed films | Thickness uniformity | +/- 10% over 100 mm | Profilometry / AFM |
| Conductive features | Resistivity (Ag, sintered) | < 10x bulk Ag | 4-point probe |
| Multi-layer registration | Alignment accuracy | +/- 5 micrometres | Fiducial mark detection |
| Defect density | Pinholes per unit area | < 0.1 per cm2 | Automated optical inspection |
Q1: What types of nanoparticles can be used in nano ink jet printing per IEC/IEEE 62659?
A: The standard applies to inks containing metallic nanoparticles (silver, gold, copper, nickel), metal oxides (ITO, ZnO, TiO2), carbon-based nanomaterials (carbon nanotubes, graphene, carbon black), semiconducting quantum dots, polymeric nanoparticles, and biologically active compounds. The key requirement is that the nanoparticle size be less than 1/50th of the printhead nozzle diameter to prevent clogging.
A: The standard applies to inks containing metallic nanoparticles (silver, gold, copper, nickel), metal oxides (ITO, ZnO, TiO2), carbon-based nanomaterials (carbon nanotubes, graphene, carbon black), semiconducting quantum dots, polymeric nanoparticles, and biologically active compounds. The key requirement is that the nanoparticle size be less than 1/50th of the printhead nozzle diameter to prevent clogging.
Q2: What are the advantages of nano ink jet printing compared to conventional lithography?
A: Nano ink jet printing is an additive, mask-less process that eliminates multiple lithography steps including resist coating, exposure, development, etching, and stripping. It offers digital design flexibility, rapid prototyping capability, reduced material waste (typically 90-95% material utilization vs. 10-20% for subtractive processes), and compatibility with flexible and non-planar substrates. However, it typically offers lower resolution than photolithography (20-50 micrometre minimum feature size vs. sub-10 nm for advanced lithography), making it suitable for applications where cost and process simplicity are prioritized over extreme miniaturization.
A: Nano ink jet printing is an additive, mask-less process that eliminates multiple lithography steps including resist coating, exposure, development, etching, and stripping. It offers digital design flexibility, rapid prototyping capability, reduced material waste (typically 90-95% material utilization vs. 10-20% for subtractive processes), and compatibility with flexible and non-planar substrates. However, it typically offers lower resolution than photolithography (20-50 micrometre minimum feature size vs. sub-10 nm for advanced lithography), making it suitable for applications where cost and process simplicity are prioritized over extreme miniaturization.
Q3: How is the printed feature conductivity improved after printing?
A: Post-printing sintering is required to achieve functional conductivity. The three main methods are: (1) thermal sintering (120-250 deg C for 10-60 minutes), which provides the highest conductivity but limits substrate choice; (2) photonic sintering (intense pulsed light, milliseconds), which enables room-temperature processing on heat-sensitive substrates; and (3) chemical sintering (vapour or liquid-phase treatment), which achieves conductivity at low temperatures but may require additional processing steps. The choice of sintering method depends on the substrate thermal budget, throughput requirements, and desired final conductivity.
A: Post-printing sintering is required to achieve functional conductivity. The three main methods are: (1) thermal sintering (120-250 deg C for 10-60 minutes), which provides the highest conductivity but limits substrate choice; (2) photonic sintering (intense pulsed light, milliseconds), which enables room-temperature processing on heat-sensitive substrates; and (3) chemical sintering (vapour or liquid-phase treatment), which achieves conductivity at low temperatures but may require additional processing steps. The choice of sintering method depends on the substrate thermal budget, throughput requirements, and desired final conductivity.
Q4: What is the maximum production throughput achievable with nano ink jet printing?
A: Industrial-scale nano ink jet printing systems using multi-nozzle printheads (hundreds to thousands of nozzles) can achieve throughputs of 10-100 m2 per hour for printed electronics applications. The limiting factors are the printhead firing frequency (typically 20-100 kHz), the number of nozzles, the required print resolution, and the number of printed layers. For high-volume applications such as RFID tag production, roll-to-roll systems operating at web speeds of 10-50 m/min are commercially available.
A: Industrial-scale nano ink jet printing systems using multi-nozzle printheads (hundreds to thousands of nozzles) can achieve throughputs of 10-100 m2 per hour for printed electronics applications. The limiting factors are the printhead firing frequency (typically 20-100 kHz), the number of nozzles, the required print resolution, and the number of printed layers. For high-volume applications such as RFID tag production, roll-to-roll systems operating at web speeds of 10-50 m/min are commercially available.
