Preparation and Properties of Low Internal Stress Polyimide‑b‑Polysiloxane with a Hyperbranched Structure

Polyimides (PIs) with excellent thermal stability, mechanical toughness, dielectric properties, and an inherently low coefficient of thermal expansion are widely applied in modern microelectronic fields expectedly. However, it is still a challenge to minimize the internal stress between the PI and substrates. Herein, a series of linear and hyperbranched polyimides and polyimide-b-polysiloxane copolymers were fabricated to tailor the modulus and the coefficient of thermal expansion. Their thermomechanical properties, dimensional stabilities, and thermal stabilities were characterized by dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), and thermal gravimetric analysis (TGA), and the phase separation morphology of polyimide-b-polysiloxane was investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results showed that the internal stress of hyperbranched polyimide decreased by 11.00% compared with linear polyimide, while with the copolymerization of polyimides and polysiloxanes, the internal stress decreased by 54.62%. The hyperbranched polyimide-b-polysiloxane with a lower modulus has a CTE value of 20.1 ppm/°C close to the CTE of copper, which has tremendous potential to be applied in chip-scale packaging.