Synthesis of poly (amic ester) with controlled molecular weight for photosensitive polyimide in advanced package

Photosensitive polyimide (PSPI) with excellent lithography patterning and superior comprehensive properties have emerged as a very promising material for the advanced electronic package in IC field. Thereinto, poly (amic ester) (PAE) with highly sensitive groups and suitable molecular weight becomes the most important component in PSPI. Herein, a series of PAEs are synthesized by 4,4-oxydiphthalic anhydride, 4,4′-oxydianiline, and 2-hydroxyethyl methacrylate. The molecular weight of PAE was carefully controlled by using phthalic anhydride as the end-capping agent ranging from 9 000–20 000 g/mol. With the cooperation of photoinitiator and crosslinker, high-performance PSPIs were obtained. The results showed that the PAE with a molecular weight of 15 000 g/mol showed the best performance of lithography with resolution of 10 µm. The further increase of the molecular weight resulted the residues after developing, while lower molecular weight exhibited partially imidization during the pre-baking process, leading to a decrease in the solubility of PAE, as well. Additionally, as-prepared PSPIs also performed excellent thermal, mechanical, and dielectric properties, showing tensile strength of 120 MPa, elongation at break of 8%, glass transition temperature and the temperature of 5% weight loss of 260 °C and 430 °C, respectively. All these results exhibit a great application potential for high performance advanced packaging.