Material Jetting (MJ) is transforming Additive Manufacturing (AM) by providing a high-resolution technique for efficiently depositing material droplets to create complex structures. This article discusses the creation and synthesis of a state-of-the-art polyimide precursor ink specifically made for MJ, which makes it possible to produce high-performance polyimide films. By selectively depositing conductive silver tracks and polyimide dielectric layers, the special formulation makes it easier to create complicated circuit board designs. This increases design freedom for high-performance Printed Circuit Boards (PCBs) that are more efficient and compact.
With this less complicated method for making double-sided PCBs, we can achieve higher circuit densities. An insulating material is selectively deposited at the cross-over spots, providing an insulating bridge for the circuit, as opposed to isolating the entire circuit using a dielectric plate, commonly done in double-sided PCB. Controlling film topography and removing defects such “coffee stain” drying, cracking, and delamination are crucial when printing these local insulators. As a result, a dependable insulator with exceptional film and dielectric attributes is needed.
Engineered polymers such as Polyimide Inks are renowned for their superior mechanical, electrical, and chemical resistance as well as their outstanding thermal stability. The microelectronic industry finds this material especially appealing, as it finds significant uses in interlayer dielectrics, protective layers in integrated circuit production, and microelectromechanical system (MEMS) devices.
Polyimide Ink Synthesis
The polyimide precursor ink was meticulously crafted, combining 4,4′-isopropylidenediphenyl-1,1′-diyldioxy dianiline (BAPP), maleic anhydride (MA), and other components. This ink demonstrated excellent printability, achieving a printing indicator Z of 3.98, falling within the printable range. The ink’s formulation allowed for the creation of uniform and dense polyimide films through reactive MJ, employing a real-time thermo-imidisation process.
Effects of Substrate Temperature
The substrate temperature during printing played a crucial role in determining the surface morphology of the printed structure. Varied substrate temperatures (120 °C, 150 °C, and 180 °C) were explored in Figure 1, showcasing how higher temperatures led to decreased droplet diameter but increased thickness. This resulted in improved surface quality, reduced roughness, and sharper film edges.
Thermal Imidisation Process: The conversion of the polyimide precursor ink into polyimide was initiated through simultaneous solvent evaporation and thermal imidisation. Fourier Transform-Infrared Red (FT-IR) spectroscopy confirmed the degree of imidisation, with a peak at 1375 cm−1 indicating the transformation. Additional post-treatment at 180 °C for 15 minutes significantly enhanced imidisation conversion, highlighting the importance of controlled heating.
Printed PI Films as Dielectric Insulators: The dielectric constant of the printed polyimide film was characterized, yielding a value of 3.41 ± 0.09, comparable to commercial polyimide films. Selective deposition of polyimide insulators onto silver tracks demonstrated the potential for creating complex circuit board structures. The technique involved printing square polyimide insulators between crossed silver conductive tracks, showcasing successful functionality and avoiding short circuit issues.
To demonstrate the capability of producing a single sided circuit board with two overlapped circuit patterns through material jetting, a demonstrator was produced by subsequently printing circuit one followed by polyimide insulator deposited on the designed overlap locations and then circuit pattern two (Figure 2).
This has been a groundbreaking inkjet printing technique for the efficient fabrication of advanced circuit boards. By leveraging a specially formulated polyimide precursor ink, it has successfully demonstrated the selective deposition of high-performance polyimide insulators alongside conductive tracks. This innovative approach presents a continuous process for 3D printing complex circuits, providing a more versatile and cost-effective alternative to traditional manufacturing methods which open new possibilities for the widespread use of functional polymeric materials in Additive Manufacturing.
We support a wide range of insulating polyimide inks and we can produce new grades after consultation with our R&D department. Take the next step toward material excellence and development – reach out to our team today.
