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EE CAD Terminology
From Transwiki
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[edit] General EE CAD terminology
[edit] Component
An object which can be placed into a design. Examples : a Resistor, Capacitor or chip.
[edit] ECO
ECO stands for Engineering Change Order and refers to design changes to circuits after they have been wholely or partially completed. ECOs document the approval of changes that correct design errors or changes of part type sometimes made due to part availability. The term ECO has come to mean the process of making a change to a design - not only the paper work involved.
- There are two kinds of ECOs referred to in EE CAD systems: Forward and backward
- A forward ECO would be where a change or changes are made to the schematic that needs to be 'forwarded' to the PCB design.
- A backward ECO is where a change is made to the PCB and the changes need to be reflected 'back' into the schematic. Backward ECOs only make sense in a few situations - such as renumbering the reference numbers based on placement on the Circuit board.
- Good design practice often uses revision numbers in a decimal form '2.3' - the major number (2) refers to the revision of circuit board and the minor number (3) would be the changes in the schematic and parts list. (Some minor revisions are made to the circuit board in the form of cut traces and tacked on jumpers). By renaming the schematic and circuit board file after every change, one has a history to look at. ECOs would also have text file explaining the what and why things were changed and sometimes someone signs off on approving the changes. (This keeps purchasing from replacing a 10uf/10V tantalum with a 10uf/6V tantalum!)
[edit] Fields
Fields known as part attributes in other CAD packages - includes things like value, tolerance, footprint, price, manufacturer, vendor, description.
[edit] Footprint
Kicad sometimes calls these modules - they are also known as a decals, or patterns. A footprint is the graphics that represents the component in the PCB layout program (pcbnew). A footprint is a grouped set of PCB pads and component overlay shapes that define the space required to mount and connect the physical component on the board layout.
[edit] Modules
Modules are foot-prints or PCB decals - the art work that appears on the PCB
[edit] Reference numbers
Designators, such as R1 or U2 that refer to parts and the associated schematic element.
[edit] Symbol
A graphical representation of the component, that is placed on the schematic. The symbol can include drawing objects that define the shape, and pins that define the electrical connection points.
[edit] Units
Units known to the rest of the EE CAD world as gates! Certain components, such as a quad op-amp, resistor network or even a relay, can be drawn as a series of separate parts, which can be placed independently on the schematic (referred to as a multi-part component). The component is made up of these Units (or gates).
[edit] Value
value eeschema uses the field name 'value' to mean part-name or part-type.
[edit] File Formats
[edit] Gerber File format
D codes (See "Gerber RS-274X format" docs and http://en.wikipedia.org/wiki/Gerber_File)
