Cadance OrCAD Layout Capture is the central schematic entry program in the three program suite by Cadance called OrCAD. This suite also consists of Pspice (circuit simulation software) and Layout (circuit board layout) packages. All applications begin with Capture. Overview: This simple tutorial is designed to walk the user through a very basic PCB board design layout providing some hints along the way. It does NOT cover all of the features of Layout, so become familiar with the online manuals that come with the package. Mechanical Design: Designing a PCB is as much a mechanical engineering problem as it is an electrical one. Important issues to considerBEFORE designing the PCB are: Packaging- Is the PCB going into an enclosure? If so, you should have a sample of the enclosure to test fit the d esign. How will I mount the PCB to the enclosure? Think about mounting holes and standoffs. At least 3 fasteners are required for PCB stability. Make sure you design in enough clearances so the PCB and components don’t hit. Is the design serviceable? On a prototype, plan on disassembling and reassembling it often during the development process. Having to unsolder wires or remove connectors would have a majorimpact on the development time. What about board height? Because the Layout CAD packages are all 2D this is one area where many mistakes are made. Be sure to design the package so the tallest components clear. Be sure the components that generate heat have adequate ventilation. If a component needs a heatsink be sure to check for clearance with adjacent components. Connectors: Connectors are another major source of problems. Check to be sure there is enough clearance, not only for the connector on the PCB, but also the mating connector. Using a wire harness for off board componen ts like potentiometers, connectors, and
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displays can be time consuming and cause reliability issues.
Think about mounting as many system components as possible directly to
the PCB.
Component Selection Criteria:
You have to think of the components in their physical form not just their electrical properties.
Ask yourself what are the most important aspects of this design. (Size, ease of assembly,
cost, availability of parts etc.)Many electronic components may not be readily available in all package styles.
Investigate this BEFORE you start to design a board. Even if the manufacturer makes a
particular style it doesn’t mean vendors will stock it.
Through hole components, ones that have leads that go through a hole in the PCB andsolder to a pad on the solder side, are the easiest to work with.
However, some of the newer Integrated Circuits are not available in this package style.
Surface mount components are small but more difficult to work with.
They mount on pads that can be very close together making assembly difficult. Starting the Design:Since there can be many choices in packaging for an individual part, the best approach is
to first gather information on the package type you intend to use.
For all of the components in your design, copy the pages from the data sheets that show
the mechanical package you will be using.Data sheets are available online from the manufacturer or the vendor such as
www.digikey.com
Don’t overlook minor components like resistors and capacitors. They are available in awide range of sizes and styles.
Connectors are especially important. The standards for connectors may not be uniform
so extra care must be taken to be sure the footprint selected is IDENTICAL to the one inthe data sheet. A footprint is the size and shape of the conductors and mounting holes of
the component.
It is HIGHLY recommended that you have an actual sample of all the parts in the design before designing the PCB.
Running the Applications:Schematics are drawn using Capture just as they are for documentation only applications(see help file on OrCAD Capture).
Additionally, in Capture you will need to edit the properties of the parts and specify a
Compare the data sheet information you have gathered against these libraries and recordthe correct library for each component.
If your footprint is not in the standard library you will have to make one.
Running through this following example will get you familiar with the Library editor, butyou should consult the on-line manuals for help in creating a part footprint.
Creating the Schematic:
The schematic is created just like a documentation only schematic. (See MTC OrCAD
Capture help example)
Lets look at the same schematic we created in the MTC OrCAD Capture help procedure.
It’s a simple through hole design with 2 connectors, a LM741 opamp, and two ¼ Wresistors.
The white text is the silkscreen that will be printed on the board.Select “Tool” “Text” and click on the “6” for the first mounting hole and delete. (We
don’t need markers for holes)
Repeat for the other holes.With this tool you can move text around or create text using the “New” feature.