Design and Optimization of Driving Waveform for Inkjet Printing Photoresist with UltraLow Viscosity

An optimization method based on a dual negative voltage driving waveform is proposed to address the droplet jetting instability caused by residual oscillations in piezoelectric drop-on-demand (DOD) inkjet printing of ultralow viscosity photoresist (0.71 mPa·s). The experimental system for photoresist droplet ejection and observation is developed to systematically investigate the effect of driving waveform parameters on droplet generation. Experimental results demonstrate that the designed dual negative voltage driving waveform effectively suppresses residual oscillations and significantly improves the stability of photoresist droplet jetting by introducing a suppression negative voltage into the traditional drive waveform. Furthermore, by optimizing the timing parameters, the optimal duration and interval time of the suppression voltage are determined to be t₃ = 2.4 μs and Δt₂ = 4.1 μs, respectively, enabling uniform and stable photoresist droplet jetting from three-phase nozzles without satellite droplets. Moreover, the effects of printhead driving parameters on droplet characteristics are quantitatively explored. The optimal droplet diameter and ejection velocity are 23.20 μm and 9.51 m/s at the driving voltage and frequency of 6.3 V and 5 kHz, respectively. This work not only provides a feasible waveform design strategy for stable droplet jetting of ultralow viscosity photoresist but also lays a solid foundation for the application of inkjet technology in semiconductor wafer-level packaging.