PCBDesign.pdf
- 1. Designing a PCB EE155/255 - Fall 2015 Ned Danyliw
- 2. Why a PCB? • Permanent, repeatable (hopefully) circuit • Lower parasitics • Necessary for high speed designs • Smaller form factor
- 3. Cross-section of a PCB
- 4. Designing a PCB • Design the schematic • Select the components • Place components on PCB • Route signals and power planes • Send design to manufacturer • Assemble
- 5. Software • Free software • Eagle • Probably the most popular • Free • Huge library of pre-made components • Free version - 2 layer and limited PCB size • FreePCB • KiCAD • Paid software • Altium • Prohibitively expensive for personal projects • Much easier to route large designs
- 6. Schematic Design • Flexibility is good. You don’t need to populate every component. • Make sure components are properly bypassed • Typically a .1µF capacitor on their supplies • Clearly label parts • Named nets are good • Organize schematic logically
- 7. Component Selection • Build bill of materials with components supplier • Preferably a single supplier • Digikey, Mouser, Jameco, etc. • Be aware of package size/code • Always check the datasheet • Order typically 3x
- 8. Board Layout Pt. 1 • Most important step in designing a PCB • Intelligent placement makes routing easy • Typically can place circuit in “blocks” • Keep components close together (shorter traces typically are better) • Keep power dissipation in mind (spacing/trace widths) • Clearance for connectors • Separate “noisy” and “quiet” signals • Add test points
- 9. Board Layout Pt. 2 • Route the critical signals (critical power loop, high speed digital, analog signals, etc.) • Don’t autoroute*!!!!!! • Often power signals should use polygons • In general traces should be as wide as they possibly can • Run DRC (design rule check) often! • With multiple layers, map what each layer (generally) is for *can use autoroute tools for some signals but you need to know what you are doing
- 10. Design Example • Microcontroller board for littlebox • STM32 microcontroller • Instrumentation amplifiers for sensors • Boost converter • Interface with 3 other boards
- 11. Schematic
- 12. Boost Schematic
- 13. µC Schematic
- 14. Planning • Mechanical considerations for component placement • Account for connectors and required positions • Mounting holes • Heat sink placement • Low inductance switching loop • High current traces • Noisy/quiet power planes
- 16. Route Signals
- 17. Add Polygons
- 18. Critical Loop
- 19. Many Iterations
- 21. General Hints • Design in stages • Frequently review layout and check for errors • Keep notes • Leave testpoints • If possible leave pads for circuit adjustments