The invention discloses a manufacturing processing of making a flexible printed circuit for inkjet printheads. Through the change of the flexible printed circuit structure, residual stress at the bent part can be reduced and the efficiency and precision of subsequent processes can be increased. The disclosed process is thus able to make products with high reliability and quality. The process involves the steps of: (1) preparing a flexible printed circuit substrate and making a window at a predetermined bent part; (2) coating the substrate with a metal layer so that the substrate become conductive; (3) etching the metal layer through a photolithography process to produce a conductive circuit on the flexible printed circuit; and (4) forming a cover layer (solder mask materials such as epoxy or acrylic resins) at the window. A flexible printed circuit thus produced is pre-bent, easy to attach and align, and has less residual stress and a cover layer or film at the bent part.