User:Rob Kam/sandbox1/PCB layout and design

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Creating a board shape that fits the physical size requirements, positioning the mounting and tooling features, determining the number of routing layers (cost vs. performance), logically arranging circuits into functional areas (floor-planning), populating each area with appropriate land patterns (placement), adding planes & traces to connect everything together (routing), generating data to fabricate, assemble and test the product

Basic guidelines

• it is often a good idea to have made a prototype circuit using point-to-point construction or wire wrap, as you will have solved certain basic issues to do with component selection: (e.g., should I use a 1/4 watt resistor here, or do I need 1/2 watt?)
• consider physical constraints on the assembled board's size and heat dissipation requirements; choose your heat sinks if needed.
• consider carefully the physical size of the components you are laying out; the circuit schematic doesn't tell you this. Equivalent components often have different packages.
• How do the components attach to the board? Are they surface mount components? or do they require holes, screws, washers, etc.?
• are there mechanical parts directly mounted to the board? For example, switches or variable resistors?
• How will the board mount in its container? What stresses (shock, strain, shear) will there be upon it and upon components?
• How will the board connect to its power source? What other connectors will be required (e.g., signal inputs, outputs)?
• use construction paper and a pencil and sketch the board in its actual size; or use component layout software that includes information about the component outlines.
• decide appropriate widths for each of the signal traces; this depends on the current each trace is expected to carry.
• decide whether you will have a single-layer board, 2-layer, or multi-layer based on the circuit complexity and fabrication costs.
• begin by placing component outlines, then by placing signal traces; leave a little room around each for tolerances.
• for a single layer board, spend more effort to avoid having traces cross each other; play with component placement or run traces underneath components; sometimes a jumper wire is needed.
• in 2-layer and multilayer boards simply run the traces on different layers, and use plated-through holes to jump from one layer to another.
• try to predict and avoid assembly errors: where there are multiple components of the same kind, or where pins have a polarity (e.g., electrolytic capacitors), try to place them in parallel and orient the positive pin in the same direction.
• If your PCB design software has a DRC (design rule check), use it.
• print your board layouts on paper. This is especially useful when working with unfamiliar components to verify the footprint, but it's also use just to get a sense of scale and spacing.

Further reading

• The Circuit Designer's Companion by Peter Wilson, Newnes, 2017, ISBN 9780081017647
• Fundamentals of Layout Design for Electronic Circuits by Jens Lienig, Juergen Scheible, Springer, 2021, ISBN 3030392864

External links

• PCB design books, Synth-DIY email list, Mar 2022

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