Low‐temperature curable, alkaline‐developable, and negative‐type photosensitive polyimide with high resolution and mechanical properties based on chain extendable poly(amic acid) and photo‐base generator

A negative‐type photosensitive polyimide (PSPI) based on a chain extendable poly(amic acid) (PAA) and a photo‐base generator (PBG) (E)‐1‐piperidino‐3‐(2‐hydroxyphenyl)‐2‐propen‐1‐one (PHPP) have been developed. The chain extendable PAA was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianiline (ODA) and end‐capped with di‐tert‐butyl dicarbonate (DIBOC) in N‐methyl‐2‐pyrrolidone (NMP), which has a controlled molecular weight for developing in a 2.38 wt% tetramethyl ammonium hydroxide aqueous solution (TMAHaq) and underwent a chain‐extending reaction during a curing stage. The PSPI was formulated with the polymerization solution (20 wt% in NMP) and PHPP (15 wt% for the polymer). The PSPI showed a sensitivity of 152 mJ cm−2 and a contrast of 5.9 when exposed to the i‐line, followed by post exposure baking at 160°C for 2 minutes and development with the 2.38 wt% TMAHaq containing 10 wt% iPrOH at room temperature. A fine negative image with 2‐μm pattern was obtained on a 3‐μm thick film in the contact‐printed mode. After thermal curing at 200°C for 1 hour, the resulting PSPI features low curable temperature, high resolution and excellent mechanical properties.