Master of Science in Mechanical Engineering (MSME)


Mechanical Engineering

Document Type



The LIGA process potentially enables economic mass-production of devices with high aspect ratio geometry. Central to the LIGA process is the fabrication of high quality LIGA molds. But in the traditional LIGA mold insert fabrication process, the x-ray photoresist poly-methyl-methacrylate (PMMA) is not highly sensitive to x-rays and a thick piece of PMMA sheet (>1mm) needs too much time to get exposed (bottom dose: 3500J/cm3), which results in excessive cost/ fabrication difficulty of the mold insert. Thus, in this thesis a negative photoresist SU-8 was tested as an x-ray photoresist in the LIGA fabrication process. SU-8 is much more sensitive (bottom dose: 20 J/cm3) than PMMA to x-rays, and the exposure time for SU-8 is decreased by a factor of a few hundred compared to PMMA, which is the primary motivation of this thesis. From the preparation of SU-8 samples to the removal of exposed SU-8 embedded in the electroplated nickel mold insert, the whole procedure for LIGA mold insert fabrication using SU-8 photoresist was successfully developed in this thesis. Compared with several other removal methods, ashing in nitrogen was selected as the method to remove the SU-8 embedded in the electroplated nickel mold insert because it is effective and inexpensive. Next the Scanning Electron Microscope (SEM) photos were taken to analyze the removal of the SU-8. Since the SU-8 removal was involved a high temperature (600„aC) step, the mechanical properties of the mold insert were degraded. Therefore, the strength and microhardness were tested to quantify the degradation. It was found that the microhardness was reduced about 46.8% and the modulus of rupture was reduced about 38%. For most applications, the degradation of strength and hardness is still acceptable.



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Committee Chair

Kevin W. Kelly