One of the most fascinating and critical steps in the manufacturing process is the imaging step. This is the step where the digital representation of the PCB is transferred to a physical manufacturing panel and where the PCB begins to take on its designed form.
Manufacturing panels (either internal cores or outer layer panels) are most commonly coated with a dry film material. This dry film is a photo sensitive polymer that is applied to the panel through a lamination process, where heat and pressure adhere the dry film to the external copper layers of the panel. An L.D.I. (laser direct image) printer exposes the dry film much like a laser printer does with ink and paper, transferring the PCB image to the panel. When the dry film is exposed to this high intensity laser light, it physically cross-links the polymer.
The portions of the dry film that are not exposed to the laser will become the PCB’s circuitry, pads and other copper features (on an outer layer panel). Once the dry film has been exposed, it is then developed. All of the unexposed dry film is chemically removed creating a copper plating mask. Areas of exposed copper will be copper plated and eventually the areas under the exposed dry-film will be etched away, defining all of the circuitry.