Novel ultra-low-modulus flame retardant polyimides for cover layer materials

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Two types of ultra-low-modulus polyimides (PIs) with/without photosensitivity were developed as novel cover layer materials for applications to flexible printed circuit boards (FPC) in this work. Our photosensitive PI cast film exhibited an extremely low tensile modulus of 0.28 GPa, which is low enough for avoiding an undesirable FPC curling phenomenon, in addition to the highest level of non-flammability (UL-94, VTM-0), compatibility to the solder reflow process, good photosensitivity for fine pattern formation. We also developed novel screen-printable ultra-low-modulus copolyimides systems without photosensitivity. The copolyimides displayed an extremely low modulus of 0.015 GPa and an excellent adhesion strength with copper foil (2.3 kgf/cm)