Researchers based at the University of Texas at El Paso (UTEP) have developed a new low-cost Aerosol Jet Printing (AJP) system that’s capable of fabricating hybrid electronic devices.
Costing just $12,000, the scientists’ 3D printer is based on a 32-bit microcontroller (MCU), which allows it to connect with peripherals that give it advanced patterning capabilities. Using its flexible functionality, the machine is able to deposit electronic inks into complex designs, potentially making it a more attainable method of fabricating electronics within research, prototyping and educational applications.
Making AJP more attainable
Digital motion control systems represent a core component of many 3D printers, not just within AJP setups, but FFF, material jetting and sheet lamination systems as well. Essentially, the devices are used to orient a system’s toolheads during printing, and the prevalence of low-cost MCUs within FFF, has been key to the technology’s adoption within labs, maker spaces and academic settings.
However, accessible motion control systems have traditionally been limited by low-precision, making them less useful within AJP machines which operate in the 10-100 µm range. AJP MCUs also need to be capable of extensive multi-tasking in order to create commercial-standard electronics, often necessitating the inclusion of pricey beefed-up hardware.
What’s more, high-performance microcontrollers are often built with proprietary software, inhibiting the ability of owners to customize their machines for specific applications. In an attempt to make AJP more accessible, the UTEP scientists have therefore developed a cheaper architecture, along with a supporting Real-Time Operating System (RTOS), that’s capable of handling multiple tasks on the move.
AJP printing on a budget
Due to its competitive specs, the team opted to use a $40 Texas Instruments Cortex-M4F MCU, as a basis for their new machine. Featuring a built-in UART transmitter and (I2C) circuit interfaces, the microcontroller possessed sufficient capacity to control the printer, while synchronizing peripherals with its motion control system at the same time.
The MCU was built into a custom-AJP printer, characterized by a 3-axis motor platform, as well as a relay module, mechanical shutter and ultrasonic nebulizer for ink atomization. To provide their system with high-speed processing capabilities, the team then used the FreeRTOS application to create an OS which broke its operations down into simple tasks, making them both manageable and modular.
Once the scientists had perfected their algorithm and assembled their system, they armed it with a silver ink, and fabricated a series of symmetrical patterns. Having passed initial tests with flying colors, the researchers went on to assess their machine’s suitability for more demanding applications, by depositing conductive silver into a ‘serpentine’ resistor.
The resulting detector featured temperature-sensing functionality, and proved capable of providing an exact read-out, during both heating and cooling evaluations. However, while the team’s machine was able to achieve a print resolution of 50 µm, some of their more complex test objects exhibited ink spreading, and they surmised that this could be rectified by adding a heated bed, for greater control over deposition rates.
The step-rate of the scientists’ AJP machine was also quicker than that of low-cost FFF systems, but remained slower than many high-end printers. To rectify this, the team suggested that their approach can be further optimized via upgrades to their algorithm, and identified particular opportunities for improvement within time-critical parts such as their machine’s shutter.
In the near future, the engineers also intend to make the precise specifications of their low-cost AJP 3D printer openly-available via GitHub, with the aim of making its electronic 3D printing capabilities available to as many users as possible. In the meantime, a brief breakdown of the custom system can be found below.
| Specification | Details | |
| Print resolution | 50 µm | Ink/parameter dependent |
| Print speed | 20 mm/s | At ~0.5 µm step size |
| Pulse rate | 30 kHz | Per axis, XY bidirectional |
| Interpolation | Linear | Look-ahead in future development |
| Safety features | Emergency button | Soft/controlled abort |
| Supported files | RS-274 Gcode | Custom M codes implemented |
| Custom MCU commands | Programmatic toolpaths possible | |
| Feedback data | Motor position, MFC pressure | User-configured data rate |
AJP’s electronic applications
During AJP, it’s essentially possible to spray conductive inks onto either 2D or 3D surfaces, making it ideal for producing PCBs and consumer electronic devices.
Albuquerque-based Optomec is somewhat of a specialist in this area, and it recently launched its Aerosol Jet HD2 3D printer, which is specifically designed to create 5G circuit boards. Elsewhere, the company’s technology has also been installed by Samsung Electronics, as a means of expediting its electronics production process.
On a more experimental note, researchers at Carnegie Mellon University have been awarded $1.95 million to develop a new class of AJP 3D printed neural probes. Through their project, the team aims to create a low-cost repeatable method of producing brain implants, with neurological monitoring capabilities.
Similarly, scientists from the Georgia Institute of Technology and Hanyang University have developed a novel AJP 3D printed blood-monitoring biosensor. The stretchable electronic system features a circuit-free and low-profile design, allowing it to be deployed as a means of identifying brain aneurysm treatments.
The researchers’ findings are detailed in their paper titled “Modular motion control software development to support a versatile, low-cost aerosol jet platform for printed electronics. ” The study was co-authored by Alejandro Martinez-Acosta, Rebecca R. Tafoya, Stella A. Quinones and Ethan B. Secor of the University of Texas at El Paso, Sandia National Laboratories and Iowa State University.
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Featured image shows the low-cost components of the researchers’ AJP 3D printer. Photo via the Additive Manufacturing journal.
