Difference between revisions of "PCB Design"

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** Width: 10 mils / 0.254 mm
** Width: 10 mils / 0.254 mm
* '''Distance to board edge:'''
* '''Distance to board edge:'''
** Isolation: 12-50 mils / 0.3048-1.27 mm - for clean cut or v-score of the boards
** Isolation: 12-50 mils / 0.3048-1.27 mm - for clean routing cut or v-score and avoiding shortcircuitings
* '''Traces:'''
* '''Traces:'''
** Signal width: 12-16 mils / 0.254-0.4064 mm - enough distance to avoid shortcircuiting of traces
** Signal width: 12-16 mils / 0.254-0.4064 mm - enough distance to avoid shortcircuiting of traces

Revision as of 11:17, 1 May 2011

The the prototyping is done, putting the design proper PCB board makes it more rigid and possible to offer unassembled kits. The process is mostly straight forward but the design process to lay out the board requires some time to get right.

Eagle will be used here, it's cross platform and great part libraries.

Setup

  • Eagle parts libraries:
  • CAM, Computer Aided Manufacturing, to create processing files for the fab house.
    • SparkFun sfe-gerb274x.cam CAM - Excellent generator of the necessary gerber and drill files, picks the right layers
    • Creates the proper gerber files for manufacturing:
      • glt - Top copper layer, main traces
      • gbl - Bottom copper layer, same bottom
      • gto - Top silkscreen, all text, lines, illustrations can be painted on top of the soldermask
      • gbo - Bottom silkscreen, same bottom
      • gts - Top soldermask, where to put tin/gold plated pads and mask all other green/other color
      • gbs - Bottom soldermask, same bottom
      • gtp - Top solder paste stensil, only needed for assembly of parts to the board
      • txt - Drill coordinates, for vias and mounting holes

Good practices

Some of these guidelines can be used in the Design Rules property window in Eagle. The PCB manufacturer normally provide a list of minimum requirements for their equipment/method.

Design rules:

  • Clearance and spacing between traces, pads, vias, and same signal smd components, pads, vias:
    • Width: 10 mils / 0.254 mm
  • Distance to board edge:
    • Isolation: 12-50 mils / 0.3048-1.27 mm - for clean routing cut or v-score and avoiding shortcircuitings
  • Traces:
    • Signal width: 12-16 mils / 0.254-0.4064 mm - enough distance to avoid shortcircuiting of traces
    • Power width: 16-20 mils / 0.4064-0.508 mm - allow large currents to flow in vcc and ground traces
  • Via drill size:
    • Diameter: 30 mils / 0.762 mm - proper connection between layers
  • Soldermask:
    • Limit: 32 mils - little higher than vias to cover them with the mask instead of tin/gold plating
  • Labels and text:
    • Add silkscreen labels to all connections and interfacing points
  • Ground pour:
    • Add a final rectangular polygon plane over the entire design and click Ratsnest - this helps to avoid board warping, better ground and signal conditions
    • To only see the board without the pour, use Ripup on the polygon

PCB Manufacturers

A great place to start is Ladyada's PCB cost calculator. It lets you compare different manufacturers by cost per square inch. Note: Prices from 2007.

  • BatchPCB - Easy and cheap for small boards

BatchPCB order

In mid-December 2010 I tried BatchPCB, a SparkFun service, to do a sample board. The result was satisfactory. I ordered 3 pieces but got 6 back, bonus!

Timeline:

  • 2010-12-16 07:43:39 Submitted, passed, paid and pending
  • 2010-12-17 07:12:18 Processing
  • 2011-01-03 10:39:40 Shipped
  • 2011-01-13 14:39:00 Arrived

This was during the xmas holidays and shipped from US to Norway, a normal turnaround would probably be 3 weeks.

Board config

  • FR4 - Stands for Flame Retardant and 4 means woven glass reinforced epoxy resin
    • Standard 1.5 mm thickness

Tools

  • Eagle - Connect schematic and design PCB board layout
  • Viewplot - View the files coming out of Eagle for verification