The invention relates to joining plastic components into a microfluidic cartridge (20). The invention in particular relates to cartridges (20) for diagnostic analysis devices. The cartridge (20) comprises a fluidically conductive floor element (11), a cover (2), and a film (3) disposed between the elements (1, 2). The cover (2) or the floor element (1) and the film (3) comprise a filling opening (5) for filling microfluidic channels (4) in one of the elements having sample fluid. Pins (6) formed integrally with one of the board-shaped elements (1, 2) engage in corresponding holes (7) in the film (3) and the associated element (1, 2) for each.By means of deforming a pin (6), a friction fit is produced between a deformed pin and the wall of a hole, and a head (9) contacting the associated substrate in a form-fitting manner is formed. For the joining process, a press tool (12) is placed on a head end (9) of a pin (6) at a predetermined pressure P, and heat transfer into the pin (6) takes place during a weld time tS. The pin material is brought to above the glass transition temperature and/or the melting point, and a friction fit between the pin (6) and the wall of the hole (7) is formed by flowing the pin material in the hole (7).