A photoplotter is a device that uses light to produce an image on media. The electro-mechanical-optical machine was originally developed in the 1960s, and enables processes that took up to 10 hours to be completed in minutes. Data instructions, which are commonly written in Gerber format, are used to guide the machine and draw the lines and shapes needed to complete printed circuit board (PCB) designs. Laser-driven systems in the 21st century allow for more sophisticated designs and work with complex computer aided design (CAD) software.
In the photoplotter’s most basic form, images are exposed onto black and white film by a light source that is controlled by a computer. The film media is then developed using a washing and drying process. Photolithography masks for PCBs are made starting with a photoplotter, and photomasks with sub-micrometer sized features can be developed for integrated circuit production.
The vector photoplotter was a machine that overcame a major hurdle in electronics manufacturing. It had a bright lamp that enabled the machine to project an image mounted within a rotating wheel. The image was then transferred to a photosensitive film or glass. Shapes were drawn on the surface using arcs called draws, produced by a continuous beam of light, while flashes were created by shining the light at a fixed location. Information on the shape and size of lines, holes, as well as other features in the image were contained in Gerber data.
Specific sets of these data are utilized by CAD software, but laser photoplotters often use numerical data to turn the laser on or off at specific time intervals. Other data formats have been developed for photoplotting with CAD or computer aided machining (CAM) software programs. One file can be used to store data, and the large size of most data storage systems is compatible with the design processes of small and intricate circuits.
Laser photoplotter systems can focus beams on one or multiple locations. The laser beams can be modulated at high frequency rates to form detailed images. A red helium-neon laser is often used, but laser diodes and red light emitting diodes are also commonly implemented for laser photoplotting. Some machines eliminate photographic film altogether, and one system has a laser or xenon lamp that directly exposes a coated substrate to light. The photoplotter has undergone technological changes and is a valuable tool in the PCB industry as well as in graphic arts and chemical milling.