NOVELTY - A circuit board (1) has a conductor portion provided on surface (S) of substrate (2), and a joining film (4) provided in portion(s) excluding contact surface. Joining film has silicon structure comprising siloxane bond, and leaving group coupled with silicon structure. Energy is provided to region of portion(s) of leaving group existing in surface vicinity of joining film. Adhesiveness is provided to energy-provided region, and region of surface of joining film is adhered with other circuit board. Contact surface (35) and conductor portion are electrically connected.    USE - Circuit board is used for electronic device (claimed). Uses include but are not limited to light emitting diode, semiconductor laser, liquid crystal display element, electrophoretic display element, photoelectric transducer, solar cell and capacitor.    ADVANTAGE - The terminal of circuit board and conductor portion are reliably connected at low temperature. Electronic device having excellent reliability is produced.    DETAILED DESCRIPTION - A circuit board has a conductor portion provided on one surface (S) of a substrate and having contact surface contacting with terminal (3) of other circuit board, and an insulating joining film provided in surface (S) and portion(s) excluding contact surface. The joining film has silicon structure having random atomic structure comprising siloxane bond, and leaving group coupled with silicon structure. Energy is provided to region of portion(s) of leaving group existing in surface vicinity of joining film, and portion(s) of silicon structure is detached. Adhesiveness is provided to energy-provided region, and region of surface of joining film is adhered with other circuit board. The resulting contact surface and conductor portion are electrically connected. INDEPENDENT CLAIMS are included for the following:    (1) joining of circuit board; and    (2) electronic device.    DESCRIPTION OF DRAWING(S) - The drawing shows the cross-sectional view of circuit board.    Circuit board (1)    Substrate (2)    Terminal (3)    Joining film (4)    Contact surface (35)