To provide an adhesive composition and an adhesive sheet capable of low-temperature adhesion, excellent in adhesion, heat-resistance, and migration-resistance under high temperature and high humidity conditions, and particularly useful for circuit boards, and to provide a printed circuit board using the same.

Polyamide-imide is copolymerized with poly(acrylonitrile-butadiene) and dimer acid or polyester to prepare a modified polyamide-imide resin. The resultant modified polyamide-imide resin has a glass transition temperature of 120°C or higher, an inherent viscosity of 0.1 dl/g or more, and a tensile modulus of 1,500 MPa or less. Also disclosed are a heat-resistant adhesive prepared by blending a crosslinking agent with the resin, an adhesive sheet formed from the adhesive, and a printed circuit board using the sheet.

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