Synthesis and properties of 6FDA-BisAAF-PPD copolyimides for microelectronic applications

In this work, fluorine-containing copolyimides were synthesized from 6FDA dianhydride and different ratios of BisAAF and PPD diamines. Properties, such as composition, viscosity, dielectric constant, glass-transition temperature, thermal decomposition temperature, tensile characteristics, and transmittance, were investigated by using elemental analysis, viscometry, Fourier transform infrared spectrometry, differential scanning calorimetry, a thermogravimetric analyzer, a tensile tester, and UV-visible spectrophotometry. After curing at 300°C for 1 h, imidization was observed, as indicated the appearance of an absorption peak of the carbonyl of the imide at 1780 cm^-1 (C≡O asymmetry stretching). The inherent viscosity increased with an increasing PPD mole fraction, from 0.40 dL/g of pure 6FDA-BisAAF to 0.84 dL/g of pure 6FDA-PPD. The dielectric constant decreased with increasing fluorine content. The glass-transition temperature increased with an increasing PPD mole fraction; the values increased from 317°C with pure 6FDA-BisAAF polyimide to 364°C with pure 6FDA-PPD polyimide. The 5% weight loss temperature (T_d) of the copolyimides was around 530°C in air and 540°C in a nitrogen atmosphere. The tensile modulus and tensile strength gradually increased with an increasing PPD molar fraction. The transmittance of 6FDA-BisAAF-PPD copolyimides was greater than 90% at wavelengths above 500 nm.