PCB design 101

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Component selection

Film vs ceramic vs electrolytic vs tantalum

Ceramic - high frequency response due to lower inductance (therefore good HF filtering bypass incoming and outgoing noise), non-polar

Electrolytics - low cost, effective at low frequency, large capacitance, lifetime goes down and depends on temperature and voltage (therefore stick to ceramics for anolog filters), polarised

Interesting note: An electrolytic capacitor relies on an oxidisation layer as an insulator so capacitance will drift more over time if it run at low voltage

Tantalum - light, small, precise, higher cost

Film - linear characteristics (voltage-temperature-capacitance)

Reference: 1, 2

Selecting voltage rating for capacitors

Multiply voltage by 4/3 or 3/2 (electrolytic caps) and up to 2 (ceramic caps)

Reference: 1, 2, 3

Eagle

Cheatsheet

  • create schematics document in Eagle
  • Edit -> Add... -> Scroll down to frames, Choose LETTER_L
  • If silkscreen and soldermask colors are swapped in Fusion 360, then check silkscreen contours outside of the board. Also measurements are not allowed

PCB design checklist (example):

  • Rounded edges
  • Copper-plated mounting holes
  • Components aligned in a grid (vs. haphazard)
  • Actually centered aligned everything
  • No sharp corners on the traces
  • Non-standard pcb color

Fusion 360

  • Change PCB color: go back to Eagle

SMD Package Types

SMD Package Type Dimensions (mm) Dimensions (inches)
2920 7.4 x 5.1 0.29 x 0.20
2512 6.3 x 3.2 0.25 x 0.125
2010 5.0 x 2.5 0.20 x 0.10
1825 4.5 x 6.4 0.18 x 0.25
1812 4.6 x 3.0 0.18 x 0.125
1806 4.5 x 1.6 0.18 x 0.06
1210 3.2 x 2.5 0.125 x 0.10
1206 3.0 x 1.5 0.12 x 0.06
0805 2.0 x 1.3 0.08 x 0.05
0603 1.5 x 0.8 0.06 x 0.03
0402 1.0 x 0.5 0.04 x 0.02
0201 0.6 x 0.3 0.02 x 0.01
01005 0.4 x 0.2 0.016 x 0.008

Miscellaneous

The purpose of the bulk capacitor is to overcome the voltage drop caused by the inductive effects of PCB traces.

  • connector and solder in options
  • old school and SMD layout options

Through hole and SMD layout options example

  • LED indicators: battery ON, USB connected

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