Circuit board CAD Terms

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!)

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Definitions

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Component:

an object which can be placed into a design.

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Symbol:

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.

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Part:

certain components, such as a resistor network or 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).

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Footprint/pattern:

names used for the model that represents the component on the PCB layout. A footprint/pattern 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.

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