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

Area of Science:

• Materials Science
• Mechanical Engineering
• Fluid Dynamics

Background:

• Piezoelectric drop-on-demand (DOD) inkjet printing faces challenges with ultralow viscosity fluids.
• Residual oscillations in DOD printing cause droplet jetting instability.

Purpose of the Study:

• To develop an optimized dual negative voltage driving waveform for stable piezoelectric inkjet printing of ultralow viscosity photoresist.
• To investigate the impact of waveform parameters on droplet generation and stability.

Main Methods:

• Development of an experimental system for photoresist droplet ejection and observation.
• Systematic investigation of driving waveform parameters, including a novel suppression negative voltage.
• Optimization of timing parameters (duration and interval) for the suppression voltage.

Main Results:

• The dual negative voltage waveform effectively suppresses residual oscillations, enhancing jetting stability.
• Optimal timing parameters (t3 = 2.4 μs, Δt2 = 4.1 μs) achieve uniform droplet ejection without satellite droplets.
• Optimal printhead parameters (6.3 V, 5 kHz) yield a droplet diameter of 23.20 μm and ejection velocity of 9.51 m/s.

Conclusions:

• The proposed waveform design strategy enables stable droplet jetting of ultralow viscosity photoresist.
• This research provides a foundation for advanced inkjet applications in semiconductor wafer-level packaging.