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IEEE Project 2010 UW-Madison Student Chapter

IEEE Project 2010 UW-Madison Student Chapter. USB-Powered LED Color Organ Meeting 2. Agenda. PCB Terminology Basic Layout Constraints Fabrication Specs Suggested Practices. PCB Terminology. Measurements 1 mil = 0.001” Net

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IEEE Project 2010 UW-Madison Student Chapter

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  1. IEEE Project 2010UW-Madison Student Chapter USB-Powered LED Color Organ Meeting 2

  2. Agenda • PCB Terminology • Basic Layout Constraints • Fabrication Specs • Suggested Practices

  3. PCB Terminology • Measurements • 1 mil = 0.001” • Net • Electrical connection between two or more component terminals, defined in the schematic • Trace • Copper line that implements a net between two or more points (i.e. component electrodes) • Fill • An area of copper fill that is associated with a net • In EAGLE, this is done with a named polygon

  4. PCB Terminology • Via • Plated hole that connects traces or fills on opposite sides of the board; you can name vias • Thermal • Thermal relief to make soldering easier • Soldermask • Coating (typically green) on PCB that helps prevent solder bridging between pads and traces • Silkscreen • Printing (typically white) on PCB, used to indicate component names, package outlines, etc.

  5. Basic Layout Constraints • Some components must be placed close to others with very direct connections • U1, C1, C2, C3, C4 • U2, C5, C6 • U3, C9 • Some traces should be kept short • USB D+/D- • It is a good idea to isolate the LED currents from the rest of the circuit as much as possible

  6. Advanced CircuitsFabrication Specs • 2-layer FR4, 0.062”, 1 oz copper plate • Green soldermask, white silkscreen • Minimum trace width 0.006” • Minimum spacing 0.006” • Minimum hole size 0.015” • All holes will be plated-through with copper, this avoids a second drill pass after the plating process • No irregular shapes, slots or cutouts • But, you could do this after you get your board, by drawing silkscreen lines as a pattern and then cutting the PCB along them

  7. Initial Eagle Layout Your design must stay within this rectangle (100mm x 80mm) when using the freeware Version of EAGLE

  8. Suggested Practices • Use polygons for power/ground connections from USB connector to integrated circuits • The ground connections are just as important as the power connections • Signal traces 10-12 mil • Don’t go smaller than 8 mil • LED power traces 24+ mil (or use polygons) • Long LED power/signal wiring is not a problem • Keep USB data traces short and symmetric • Remember to put in mounting holes if desired

  9. Suggested Practices • Make that you have no missing connections (airwires) • Download unrouted2.ulp and run it if you can’t find the airwires • Make sure that your layout passes the Design Rules Check (DRC) • If you want to do art in the copper layer, you can create a footprint and place it in the PCB to avoid DRC errors (or, carefully approve the DRC errors that your art causes)

  10. Until we meet again… • Do your layout! • Feel free to stop by and ask Mark Allie or Mike Morrow questions at any time • Some people in the group already have layout experience, so hunt them down as well • Layout reviews in 2 weeks • Any questions? • Look for materials at http://eceserv0.ece.wisc.edu/~morrow/IEEE

  11. Thermal Relief

  12. Power/Ground Polygons 1 You pay for all the copper on the board, and then pay to have it removed!

  13. Power/Ground Polygons 2 All LED currents flow in lower ground branch 5V power fill Ground fill Some capacitors on bottom side

  14. Power/Ground Polygons 3 +5V polygon inside GND polygon Rank = 1 Rectangular GND polygon covers entire PCB area Rank = 6

  15. Power/Ground Polygons 4 More ground fill on top with gap for LED current path isolation

  16. Power/Ground Polygons 5 Gap implemented in a single polygon

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