A photoplotter is a specialized electro-opto-mechanical machine that exposes a latent image on a medium, usually high-contrast monochromatic (

black-and-white Black-and-white (B&W or B/W) images combine black and white to produce a range of achromatic brightnesses of grey. It is also known as greyscale in technical settings. Media The history of various visual media began with black and white, ...

)

photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin photographic emulsion, emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the ...

, using a light source being controlled by a

computer A computer is a machine that can be Computer programming, programmed to automatically Execution (computing), carry out sequences of arithmetic or logical operations (''computation''). Modern digital electronic computers can perform generic set ...

. Once the film has been exposed, it must be processed before it is ready for use. Photoplotters are used primarily for industrial production of printed circuit boards (PCBs) and

integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

(IC) packaging. In the PCB industry, photoplotting is the first step of making

photolithography Photolithography (also known as optical lithography) is a process used in the manufacturing of integrated circuits. It involves using light to transfer a pattern onto a substrate, typically a silicon wafer. The process begins with a photosensiti ...

masks for printed circuit boards. These masks are called ''photoplots'' and are limited in resolution by the technology in use; in 1998, photoplots with resolvable details of 2.5

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

or more were possible. Integrated circuits are made in a similar fashion utilizing ''

photomask A photomask (also simply called a mask) is an opaque plate with transparent areas that allow light to shine through in a defined pattern. Photomasks are commonly used in photolithography for the production of integrated circuits (ICs or "chips") ...

s'' with sub-micrometer feature sizes; photomasks are traditionally made by photoreducing photoplotter output. Other application of photoplotters include chemical milling and specialized graphic arts.

History

The first photoplotter was introduced by Gerber Scientific, Inc. in the 1960s. The company's file standard, the

Gerber format The Gerber format is an open, ASCII, vector format for printed circuit board (PCB) designs. It is the ''de facto'' standard used by PCB industry software to describe the printed circuit board images: copper layers, solder mask, legend, drill d ...

for PCB files, eventually became an industry standard for describing the printed circuit board images such as the copper layers, solder mask and legend. Early machines used a

xenon flash lamp A flashtube (flashlamp) produces an electrostatic discharge with an extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when tr ...

, and projected an image mounted in a rotating ''aperture wheel'' onto the photosensitive surface of the film or glass plate. The imaging head assembly traversed over the surface of the media without touching it to produce ''draws'' and ''flashes''. Draws are vectors or arcs created by continuous illumination as the imaging head moves over the photosensitive surface. A flash creates a single simple graphic in a location by shining light through an aperture of the appropriate shape at a fixed location. Modern photoplotters are generally

raster-scan A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image s ...

devices that use a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...

beam focused to one or more spots, modulated at multi-

megahertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base ...

rates to form the image. The most recent development related to photoplotting is laser direct imaging (LDI) which utilizes a high-power laser or xenon lamp to directly expose photoresist on a coated substrate instead of exposing photographic film. This eliminates the handling of photographic film. The input of photoplotters is a vector graphics file, typically in

. Manufacturers of photoplotters include Gerber Scientific,

Orbotech Orbotech Ltd. a subsidiary of KLA Corporation and a technology company used in the manufacturing of consumer and industrial products throughout the electronics and adjacent industries. The company providing electronics reading, writing, and conn ...

and Ucamco.

References

{{reflist

External links

* Ronald B. Webster
Variable Aperture Photoexposure Device
15 September 1970, 3 October 1972. Gerber variable shutter patent. Electronics manufacturing Plotters