Balancing dielectric properties and dimensional stability of poly(amide-imide) films via introducing a micro-crosslinked structure

With the rise of 5G communication technology and the development of microelectronics industry, establishing a balance between dielectric constant (Dk) and coefficient of thermal expansion (CTE) becomes significant for polyimide. Herein, a series of poly(amide-imide) (PAI) films were fabricated by using pyrophthalic dianhydride, 4,4′-diaminodiphenyl ether and 4,4′-diaminobenzanilide containing an amide structure as constitutional units; and then 1,3,5-tris(4-aminophenoxy)benzene (TAPOB) as the crosslinker was introduced to form the crosslinked structure within PAI films. The results indicated that well-designed crosslinked network could effectively balance the relationship between dimensional stability and the dielectric properties of PAI films. With the addition of just 0.1 mmol TAPOB, the Dk of corresponding PAI films decreased to 3.37 (at 105 Hz), compared with unmodified PAI films. Furthermore, the CTE of such PAI film revealed a 50.6 % reduction, revealing the superior dimensional stability. This work provides a novel strategy to design high-performance polyimide films for a practical application in flexible printed circuit board.