NOVELTY - A base material with joining film (1) consists of a joining film (3) provided on a substrate (2). The joining film consists of a silicon skeleton having an atomic structure including a siloxane bond, and leaving group consisting of organic group coupled with silicon skeleton. When the peak intensity of the joining film measured by infrared absorption spectrum method after irradiating UV ray, belonging to silicon-oxygen-silicon bond is set to 1, the peak intensity belonging to methyl group is 0.04-0.12.    USE - Base material with joining film is used for joining to-be-adhered components in manufacture of assemblies (all claimed) e.g. droplet discharge head (inkjet type recording head of inkjet printer). Can also be used for joining transistors, diodes, quartz oscillators, reflective mirrors, optical lenses, diffraction grating, optical filters, solar cells, pressure sensors, magnetic recording medium, LCD elements, and components of fuel cells.    ADVANTAGE - The base material with joining film enables efficient joining with excellent dimensional accuracy even under low temperature. The obtained assembly has excellent reliability.    DETAILED DESCRIPTION - A base material with joining film consists of a joining film provided on a substrate. The joining film consists of a silicon skeleton having an atomic structure including a siloxane bond, and leaving group consisting of organic group coupled with silicon skeleton, formed by plasma polymerization. UV ray is irradiated to the region of at least one portion of the joining film. When the leaving group existing in the surface vicinity of the joining film is detached from the silicon skeleton, adhesiveness with another to-be-adhered component is expressed in the region of the surface of joining film. When the peak intensity of the joining film measured by infrared absorption spectrum method after irradiating UV ray, belonging to silicon-oxygen-silicon bond is set to 1, the peak intensity belonging to methyl group is 0.04-0.12. An INDEPENDENT CLAIM is included for joining method, which involves preparing a base material with joining film and another to-be-adhered component, irradiating UV ray to the region of at least one portion of joining film, and bonding the base material with joining film and to-be-adhered component to obtain an assembly, such that the joining film is stuck with the to-be-adhered component.    DESCRIPTION OF DRAWING(S) - The drawing shows a longitudinal cross-sectional view of the base material with joining film.    Base material with joining film (1)    Substrate (2)    Joining film (3)