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Digital to Analog Converter
There are four principle advantages with aperture lists on raster plotters:
Aperture shapes can be easily generated in software, thus eliminating the need to design a physical wheel.
The aperture shapes can be described in the Gerber file, if certain extended-Gerber formats are supported ("RS274X", "MDA FIRE AutoPlot", etc.). This reduces chances of getting the wrong list.
More apertures can be defined on a list.
Allowable apertures sizes are typically (but not always) greater than those imposed by the physical dimensions of an aperture wheel.
D-CODE: i.e. D10, D11, D12...
SHAPE: i.e. Round, Square, Oval...
SIZE: in decimal inches, mils or metric
TYPE: Flash or Draw
Custom apertures can be accommodated but must be accompanied by a detailed dimensioned drawing.
Note: Aperture lists must be entered into our CAM software in order to correctly view your Gerber data. Aperture lists, when entered by hand, are susceptible to human error. A more desirable method is to use software to convert the supplied aperture table. Circuit Graphics has software to convert aperture lists output from the most commonly used CAD packages to a format recognizable by our CAM software. For this conversion process to work, you must tell us what your CAD package is and ensure that you do not edit the aperture file in any way. We have conversion programs for the following CAD systems:
Setup for Vector Plotters
RS-274D files were not designed to communicate any information about the apertures in use, only to specify where they are used. This has led to a great deal of confusion between designers and fabricators since designers aren't aware that a Gerber file alone is not sufficient to define the board - an external document describing the apertures is also needed.
When the Photo Plotter selects an aperture, the aperture wheel is rotated to place the desired aperture between the light source and the film. Apertures are themselves pieces of film and can be made to any shape required, although in practice this is a time-consuming process and there is a physical limitation on size.
Arcs and Circles