Synthesis and characteristics of polyimide/siloxane hybrid films for reliability adhesion

Polyimide/siloxane (PISi) hybrid films from 2,2′-bis[4-(3-aminodiphenoxy)phenyl]sulfone (m-BAPS), 3,3′-oxydiphthatic anhydride (ODPA) and p-aminopropyltrimethoxysilane (APrTS) have been successfully fabricated by an in-situ sol–gel process. The APrTS is used to introduce siloxane structure and to be the end-capped agent to control the polymer block chain length in the range of 5000–20 000 g/mol. The network structure of the PISi hybrid film is formed through the hydrolysis and condensation reactions. The PISi hybrid films with various polyimide block chain lengths are characterized with regard to the structure effect, mechanical properties, adhesion strength, adhesive melting flow and thermal stability. The result indicates that the more APrTS is contained, the shorter of the polyimide block chain length is formed and thus the lower inherent viscosity of APrTS-PAA is obtained. It is also suggested that the cross-linked density of the PISi hybrid film increases with the increase in the amount of APrTS. The network structure of the hybrid film reinforces the pure PI and makes the coefficient of thermal expansion (CTE) as well as adhesive melting flow decrease. Based on the dynamic mechanical analyses (DMA), the hybrid film with higher cross-linked density possesses superior mechanical property at elevated temperature. In addition, the introduction of APrTS causes an increase in thermal stability due to the network structure of hybrid film and the filler effect of the siloxane.