Polyimide based adhesive compositions useful in flexible circuit applications, and compositions and methods relating thereto

The low modulus polyimide adhesive compositions of the present invention contain a low modulus polyimidosiloxane polymer, a thermosetting substantially-non-halogenated epoxy (optionally including an epoxy catalyst), a plasticizer, an insoluble halogen-free flame-retardant filler, and optionally an adhesion promoter. The adhesive can be applied upon (or incorporated into) flexible circuits using a relatively low lamination temperature, generally no higher than 200, 190, 180, 175, 170, 165, 160, 155, or 150°C. The adhesive is generally resistant to unwanted curl even in cases where the adhesive polyimide and the base film polyimide have a coefficient of linear thermal expansions (measured between 50°C and 250°C) that differ by more than 10, 15, 20 25, or 30 ppm/°C.