Anisotropic dielectric properties of polyimides consisting of various molar ratios of meta to para diamine with trifluoromethyl group

A series of copolyimides based on pyromellitic dianhydride (PMDA) with vari ous molar fractions of 4,4'-(hexafluoro-isopropylidene)dianiline (4,4'-6F) and 3,3'-(hexafluoro-isopropylidene)dianiline (3,3'-6F) were synthesized by a two-step method. The five different composition copolyimides in the form of [(PMDA+3,3'-6F)(m)/(PMDA+4,4'-6F)(n)] were mainly characterized using a dielectric analyzer (DEA) by single surface sensor (in-plane direction) an d thin film parallel plate sensor (out-of-plane direction) measurements. DS C, TMA, and XRD were also used to study the structure property. The increas ing of molar ratio of para diamine in the copolyimide system up to 35% affe cted glass transition temperature, coefficient of thermal expansion, in-pla ne dielectric constant and out-of-plane dielectric constant of copolyimides , correspondingly. The in-plane dielectric constant was higher than that of the out-of plane constant for our polyimide films. Anisotropy As of the di electric constants was 0.14 for CPI(100/0)a, 0.19 for CPI(85/15)a, 0.11 for CPI(75/25)a, and 0.05 for CPI(65/35)a. The difference in curing history al so exhibited an effect on solvent diffusion behavior in our polymer system. Polymers cured at a slower curing rate had smaller CTE than that cured at a faster curing rate, as confirmed by X-ray diffraction results. Polymers w ith smaller CTEs. had larger dielectric constants at a slower curing rate, and vice versa. The experimental results suggested that CPI(65/35)a with sm aller dielectric anisotropy could solve the crosstalk problem and provide e qual electrical insulation in microelectronic devices. Therefore, a smaller and faster IC device could, it is hoped, be achieved, with smaller spacing between adjacent metal lines.