Electric field driven micro 3D printing of high-precision circuit on bismaleimide resin matrix composite

Fiber-modified bismaleimide resin matrix composites, with their excellent mechanical properties, high-temperature and corrosion-resistant characteristics. It is widely used in aerospace, smart skins, conformal antennas, electromagnetic shielding, high-frequency circuit substrates, electric heating and other fields. However, due to the non-flat, heterogeneous, and anisotropic nature of quartz fiber-reinforced bismaleimide resin matrix composites, the current challenge is to solve the simple, efficient, and low-cost fabrication of high-resolution circuits on this substrate. This paper proposed a new method for fabricating high-precision circuits based on electric field-driven micro-3D printing on quartz fiber-reinforced bismaleimide resin matrix composites.

In this study, quartz fiber-reinforced bismaleimide resin matrix composites were experimentally investigated using an electric field-driven micro-3D printing device. Firstly, the surface undulation of the composite surface was measured using a rangefinder, and the roughness of quartz fiber-reinforced bismaleimide resin matrix composites surfaces was measured using atomic force microscopy (AFM). Two-dimensional and three-dimensional models of the quartz fiber-reinforced bismaleimide resin-based composite material were established using the COMSOL Multiphysic software combined with the surface relief values measured by the distance meter. The characteristics of electric field distribution and the change rule of field strength were studied, and the strategy of stabilizing printing adjusting the threshold electric field strength was proposed. The influence of the main process parameters on the accuracy, morphology and performance of the fabricated circuits was experimentally revealed. Combined with optimized process parameters, multi-pattern micro circuits were produced. Later, a case study was conducted to investigate the effect and pattern of sintering process parameters on the resistance value of printed silver wires. And relationship between temperature distribution and temperature rise time of quartz fiber-reinforced bismaleimide resin composite-based micro-fine circuits. And the advantages and disadvantages of bonding properties between micro-fine circuits and quartz fiber-reinforced bismaleimide resin-based composites.

By using a rangefinder to measure the undulation of the surface of the composite. It was found that the difference between the lowest and the highest point could be up to about 0.15 mm. The surface roughness Ra of the selected area is 2.35 μm and Rq is 3.12 μm. The COMSOL Multiphysic software was used to conduct electric field simulation on the established three-dimensional quartz fiber reinforced bismaleimide resin composite material model. In the EHD printing mode, the electric field strength of the 12 spots differs greatly, with a maximum difference of 400 V/mm; while in the EFD printing mode, the difference of electric field intensity between the 12 points is small, with a maximum difference of 100 V/mm. The results show that the stability of the electric field strength of the EFD printing mode is relatively better and easier to be regulated when printing on quartz fiber-reinforced bismaleimide resin-based composites. Later, the reason for the change of the electric field on the surface of the composite material was analyzed by comparing the electric field strength with that of the single-component material. Due to the disordered distribution of the quartz fiber reinforcement phase in the bismaleimide resin matrix composite, the surface of the bismaleimide resin matrix composite is uneven, and the dielectric constant between the resin and the quartz fiber is different, so the polarization degree of the surface of the composite is different after applying voltage. This causes the electrostatic induction intensity between the nozzle and the composite substrate to change, and the electric field becomes unstable. At sites with low electric field strengths can cause cone jets to become unstable, affecting print results. Finally, the electric field variations were investigated building a 2D simulation model with nozzle inner diameters of 50 μm, 100 μm, 150 μm, 200 μm, and 250 μm, respectively. The pattern of variation of electric field strength for different nozzle inner diameters was derived to be the same. Under the premise of ensuring sufficient material supply, the lower limit value of the electric field strength can be raised by increasing the voltage to some extent and reducing the printing height. So that the cone jet also has a sufficient driving force at the relatively small electric field strength of the locus to realize continuous printing. Through experiments to explore the influence of various process parameters on the accuracy, appearance and performance of manufactured circuits, the optimal printing parameter ranges were obtained: applied DC voltage is 900-1300 V, printing height is 60-80 μm, printing air pressure is 200-240 kPa, and printing speed is 3-6 mm/s. The sintering temperature suitable for this experiment was 130-140℃, and the sintering time was 40-50 min. The electric heating experiments showed that the thermal response time under different voltages was about 150 s. At 3V DC voltage, the maximum temperature can reach 158℃, and the temperature distribution was uniform. In the composite substrate bonding performance experiment, the resistance change rate was around 1% after 100 adhesion experiments and 100 minute ultrasonic experiment, which proves that it has good adhesion. At a line width of 80 μm, the resistance is 0.7 Ω/mm and the conductivity is 4.0 × 10 S/m. The resistance of the silver wire decreases as the wire width increases.Conclusions: This study proposed a new method for preparing high-precision circuits on quartz fiber-reinforced bismaleimide resin matrix composites by electric field-driven micro-3D printing:(1) The characteristics of electric field distribution and the variant rule of field strength on the surface of non-flat heterogeneous composites were investigated by simulation and experiment.(2) By analyzing the electric field strength thresholds that enable stable printing, it was concluded that adjusting the voltage and print height can raise the lower limit of the electric field strength on the surface of the compound to meet the need for stable printing. The challenge of preparing micro-fine circuits on non-flat, heterogeneous, and anisotropic substrates has been solved.(3) Rhombic, hexagonal, and irregular grid patterns were successfully prepared based on the preferred process parameters. Small circuit patterns were printed as well as lighted LED arrays. The typical samples were printed with conductive up to 4.5 x 10 S/m.(4) The wire has excellent adhesion to the substrate of the composite material, and the resistance change rate was about 1% after 100 times of peeling cycle test and 100 min ultrasonic test. This circuit has excellent thermal response speed when applied to electric heating devices. The maximum temperature can reach 158℃ at 3 V, and it can achieve de-icing within 200 s. This provides a new method for the development of bismaleimide resin-composite-based circuits.