PCBs

This page contains some useful info for PCB design. I mainly use Eagle for schematic and layout work. A free version is available that runs under Linux, Mac OS X and Windows. Apart from a board size and layer restriction, the free version is excellent.

• Fabrication Specs
• Eagle Commands
• Creating Drill Files in Eagle
• Preparing Masks
• Length Converter
• Spacing Calculators

• Fabrication Specs

These are minimum specifications for York's PCB fabrication

Drilling Machine Units

Copper Thicknesses

• Eagle Commands

Automatic numbering of SMD pads. e.g. P1, P2, P3 ...

> SMD 'P1'

Create SMD pad of a certain size. Uses the current grid units.

> SMD 0.2 x 0.5

Aligning to Grid

You can easily align an off-grid component in Eagle by using the ctrl key when select the component. Ctrl left click will shift the component on-grid.

Ctrl left click

• Creating Drill Files in Eagle

This is a explanation on creating drill files in EAGLE

Drilling Machine Device Definition

The drill station at york requires a new device definition to be added to Eagle. The excerpt below creates a new device, 'YORKDRILL' that can be used in Eagle's CAM processor. Add this section to Eagle's eagle.def file found in the bin directory.

[YORKDRILL]

Type       = DrillStation
Long       = "Drill station at York"
Init       = "M48\n"                  ; Initialise
Reset      = "M30\n"
ResX       = 2540
ResY       = 2540
DrillSize  = "\n"                     ; Stop tool info output
AutoDrill  = "T%02d"                  ; Tool number
FirstDrill = 1
BeginData  = "%%\n"
Units      = MM
Select     = "%s\n"                   ; Drill change code
Drill      = "X+%06.0fY+%06.0f\n"     ; Drill command
Info       = "Drill File Info:\n"\
             "\n"\
             " Data Mode         : Absolute\n"\
             " Units             : 0.010 mm\n"\
             "\n"

Drill File

The drill file is created using the CAM processor. Use the following steps:

• Select 'YORKDRILL' as the output device
• Select an output filenmae (extension .drd)
• Select layers: Drills, Holes
• Uncheck all checkboxes
• Click 'Process Job'

NOTE: The DRD file needs to use DOS end-of-lines. So, if the file was created under linux you'll need to convert the file format.

• Preparing Masks

The most portable way to create masks is to export images from the PCB window.

If you intend to drill your board before the tracks are etched, you need to set the 'NODRILLS' option. This will show the drill holes filled. There are twos ways to do this:

• From the menu: Options->set->misc->No drills
• PCB window command: set display_mode nodrill

Note: This step is particularly important if you are creating a through plated board.

Exporting an image

First, you need to make the right layers visible. You will need both Pads and Vias visible, then the track layer you want; Top or Bottom.

To export an image, select, File->Export, then select Image. Enter the filename, select to produce a monochrome image and enter a suitable dpi. Eagle will create a .png file which contains dpi info, so the image should print out the right size.

Mirroring

You need to make sure that once the masks are printed the ink side will be against the copper. For the bottom layer this should already be the case, but the top layer needs mirroring. Just use a normal image editing tool to mirror the image file.

• Length Converter

Simple Length value converter. Fill in the 'From' field and click Convert.

From		To
mm thou inch		mm thou inch

• Spacing Calculators

Fill in your known data and select the unknown variable, then click Calculate

Variable Symbol Unknown Value Pad Diameter D Pad Spacing S Gap G Track Width T