Alkaline-developable and negative-type photosensitive polyimide with high sensitivity and excellent mechanical properties using photo-base generator

An alkaline developable and negative-type PSPI with a high sensitivity and excellent mechanical properties based on a poly(amic acid) (PAA) and a photo-base generator has been developed. The PAA was prepared by the polycondensation of p-phenylenediamine (PDA) with an equimolar of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA) and converted thermally to the corresponding polyimide, PI(PDA-BPDA/6-FDA). PI(PDA-BPDA/6-FDA) showed the high thermal and mechanical properties and the dimensional stability such as the thermal decomposition temperature of 530°C, glass transition temperature of 369°C, linear coefficient of thermal expansion of 28 ppm/K, ultimate tensile strength of 148 MPa, elongation at break of 25% and dielectric constant of 2.8. The PSPI was formulated directly from PAA(PDA-BPDA/6-FDA) with a photo-base generator (PBG), (E)-3-(2-hydroxy-4-methoxyphenyl)-1-(piperidin-1-yl)prop-2-en-1-one (HMPP) (10 wt% to PAA) and the optimized parameters for photolithographic process were investigated including the PBG content, post-exposure bake (PEB) temperature, and PEB time. The PSPI based on PAA(PDA-BPDA/6-FDA) and HMPP (10 wt% to PAA) showed a sensitivity of 114 mJ/cm² and contrast of 1.29 when exposed to 365-nm light (i-line), post-exposure baked at 160°C for 5 min, and developed with an aqueous solution of 2.38 wt% tetramethylammonium hydroxide and iso-propanol. A clear negative 8-μm features pattern was obtained by contact-printing and converted into the PI pattern upon heating at 250°C, confirming by scanning electron microscopy and infrared spectroscopy.