How to Create a Printed Circuit Board (PCB)(Section 7)

7. Appendix

    This appendix defines some common PCB terminology, provides solutions to some common problems and lists additional sources of information.

Frequently Asked Questions

How much does all this cost?

    - Well, the software is available to MSU students with computer accounts in the Computer Engineering Computer Labs. The other answer is that the OrCAD Software cost about $3,500 and the Prototyping system cost about $10,000.

How large of a PCB can be made using the ECE Shop equipment?

    - 13” x 19”

What is a padstack?

    - A padstack is a collection of information defining how a pin connects to the PCB. This padstack includes information about every layer in the board. For example, a dip chip would have a padstack defined for its pins. This padstack would define the size of the copper area around the pin on the top and the bottom of the PCB. It would also define the size of the hole to be drilled through the board.

What is a footprint?

    - A footprint is a collection of information defining how a part or component will attach and be used on the PCB. For example, a dip chip footprint would define were each of its pin holes are to be drilled relative to each other.

What is a pin?

    - Pin has several meanings. When I say pin, I generally mean “any connection on the PCB that may serve as a termination point for a route”.

What is a Gerber file?

    - A Gerber file is a file that contains the information from Layout necessary for the prototyping machine to drill, mill, and cut the PCB. You have a Gerber file for each Layer of information about the board. For example, you have a TOP Gerber file, which defines how to mill, drill, and cut the top of the board.

What is a layer?

    - Lets say you take several sheets of clear plastic and write on it. If you overlay these piece of plastic, they look like one piece that contains all the information. And yet each one only holds a part of the total writing. In the same way layout uses layers of information. In some cases the layer correspond to a physically different space such as the TOP and BOT layer and in other cases, the layers may just contain different information about the same physical space such as TOP and SST.

Troubleshooting

I edited my part symbol in Capture, but when I open my design that uses the part symbol, it is still using the old version of the part symbol.

    Capture stores the original version of your part symbol in the library you specify. When you use that part symbol in Capture, a copy is made of the original part symbol. This copy is stored in the Design Cache of your project. Thus you have edited the original, but the copy used in your schematic is still a copy of the old symbol. To updated the design cache to the new version do the following.

    In Capture's project manager window select your part symbol from the Design Cache folder. Select the menu item DesignàUpdate Cache. Now when you reenter your design schematic, you should see the updated symbol.

I edited my footprint in Layout, but when I close the Library Manager and return to the layout, it is still using the old version of the footprint

    Layout stores the original version of your footprint in the library you specify. When you use that footprint in Layout, a copy is made of the original footprint. This copy is stored under in the “Local” library. Thus you have edited the original, but the currently used footprint is still a copy of the old footprint. There are likely several ways to update footprints. One way I know is as follows.

    With the component tool select, double click on the component with the footprint of interest. On the properties screen that arises click on the “Footprint… ” button. Direct it to the original copy and select OK.

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Section

1. Overview

2. Prototyping

3. Schematic Capture

4. Physical Layout

5. Physical Creation of PCB

6. Lessons Learned and Recommendations

7. Appendix