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EE CAD Terminology
General EE CAD terminology
- back-drilled via
- back-drilled via is a normal
through-hole via in a PCB that connects two signal layers, but the
dangling stub hanging down from the last signal layer to the bottom of
the board has literally been drilled out. A drill bit with a diameter a
few mils larger than the drilled and plated hole drills a "blind" via to
within a few mils of the lowest signal layer. This removes the copper
stub and prevents a potentially disastrous resonance in the 5 to 10 GHz
range. All high-performance backplanes use back-drilled vias.
An object which can be placed into a design. Examples : a Resistor, Capacitor or chip.
- Connections between pads on a PCB. What makes up what is normally called tracks, routes, or traces.
- 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. It also can mean a
file type that contains information to make the change in a schematic
- 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
- Fields AKA part attributes in other
CAD packages - includes things like value, tolerance, footprint, price,
manufacturer, vendor, description.
- See Unit
- 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 (
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.
- In Kicad this might be thought of as unit
swap. Two identical Units can be swapped during layout to facilitate
routing. This changes the reference numbers of the schematic. (not yet
- Modules are foot-prints or PCB decals - the art work that appears on the PCB for each component. (AKA: asdecals, land patterns, cell, model)
- When there is a part with two pins that can be
interchanged ( the inputs of an and gate) they are swappable within a
Unit(gate). Being able to swap pins during layout helps untangle the
rats-nest of connection and helps with routing. The swapping causes the
schematic to change. Examples of swapable pins - the two terminals of a
resistor, or-gate. (not yet supported)
- Reference numbers
- Designators, such as R1 or U2 that refer to parts and the associated schematic element.
- An outer layer of a circuit board that
covers areas of copper that should not get solder - also helps prevent
solder bridging. The mask is represented in the negative sense - What
you see in CAD programs is where it ISN'T.
- 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
- Tented Via
- A blind or thru-via that has the exposed
surface on the primary, or secondary , or both sides of packaging and
interconnecting structure fully covered by a masking material such as a
dry film polymer covering (solder mask), etc., in order to prevent hole
access by process solution solder, or contamination.
- 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).
- value eeschema uses the field name 'value' to mean part-name or part-type.
Gerber File format
D codes (See "Gerber RS-274X format" docs and http://en.wikipedia.org/wiki/Gerber_File)