The Hitchhiker's Guide to PCB Design

The Hitchhiker's Guide to PCB Design

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35 A t this point in the project, Ian realized the power of having so much detailed information packed into the schematic, he believed anyone could perform the layout phase. However, what he failed to realize is a detailed schematic database is only the foundation for the PCB layout—not just anyone can perform a successful PCB layout. Layout must be performed by someone who understands industry standards for design and manufacturing as well as the depth of knowledge required for incorporating design for excellence. This individual is analytical enough to be able to sort through vast amounts of data, but creative and free-thinking enough to see many alternative ways to complete a design and have the intuition to choose the best one. A designer of PCBs is a person of renaissance. Component Footprint Creation Sometimes it is up to the PCB designer to create new component footprints for a design. A simple and straighforward process for footprint creation is best; it is also based on satisfying the stakeholder need to create perfect solder joints which could pass inspection of IPCs J-STD-001. If the component footprints are not correct and all assembly processes aren't taken into consideration, Assembly Manufacturing Engineers (AMEs) have a more difficult time soldering all the component pins to the PCB lands. To yield a perfect solder joint there are three basic processes: paste screening for solder deposition, automated placing of components, and oven reflow of solder. The recommendations for land geometry are almost always provided by the component manufacturer, and they are best compared to the industry standard for creation of component land geometry, IPC-7351. Setting up the Layout Design automation can help to perform the first step in the layout process using personal layout templates. These templates are con- figured to contain a designer's favorite settings for common design environment items. They are often used for setting design units, layer colors, net colors, trace widths, and via sizing. They can be modified at any time during the layout to match the requirements of the design. When setting up a new layout, design units can be set to metric or imperial units. Imperial units can be set to "inches," showing a decimal point in all values or "mils" (reflecting values in thousandths of an inch). Chapter 5 PCB Layout: Setup and Placement

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