A phosphorus (P)-containing diamine was synthesized and used as a comonomer at a minor fraction to improve insufficient non-flammability of a poly(ester imide) system as a promising candidate of base film materials in flexible printed circuit boards (FPC). The P-modified PEsI copolymer film displayed the highest level of non-flammability (UL-94, V-0) comparable to commercially available conventional aromatic PI films in addition to original excellent properties, i.e., a very high T g , a low linear coefficient of thermal expansion (15.7 ppm/K) close to copper foils, a low water absorption (0.54 %), a low linear coefficient of humidity expansion (5.53 ppm/RH%), and sufficient toughness (elongation at break = ca. 40%). This approach was also attempted for a very flammable low-modulus PI system for aiming at an application as a coating-type cover layer material in FPC.

This work proposes ultra-low-modulus polybenzoxazoles (PBOs), which was derived from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), a siloxanediamine (Si-DA), isophthaloyl chloride (IPC), and pyromellitic dianhydride (PMDA). The thermally cured PBO films achieved an ultra-low modulus (< 0.44 GPa). The PBO precursor (polyhydroxyamide, PHA) films possessed a relatively high i-line transmittance (T 365 > 44%), good tetramethylammonium hydroxide (TMAH) solubility. The PHA films dispersed diazonaphthoquinone (DNQ) allowed the formation of fine positive-tone patterns. Thus, the present ultra-low-modulus PBO systems can be promising candidates as novel buffer-coating materials in semiconductor applications.