Board characteristics:

- stacking: 2 layers, solder mask on front and back, silk screen on front
- board material: FR4, thickness 0.8 mm (1/32"), 1 oz copper
- surface finish: TBD, ENIG is preferred
- via holes: diameter is nominally 10 mil, but any size <= 15 mil can be used
- ground via of the antenna: hole diameter is nominally 8 mil, but any size
  <= 15 mil can be used
- mechanical tolerances: <= +/- 0.1 mm on all sides
- the holes for the positioning pins of the USB connector have a nominal
  diameter of 1.15 mm. The minimum finished hole size must be 1.10 mm,
  maximum 1.25 mm.


Hole for the USB connector:

The USB connector extends below (!) the surface of the PCB. For SMT, a
16-17 mm hole must be left next to the PCB's edge:

<-17mm->
+------+-------------+
|      |-            |
| Hole |     PCB     |
|      |-            |
+------+-------------+

For illustration:
http://downloads.qi-hardware.com/people/werner/wpan/tmp/usb-off-board.jpg


Layer stacking, from top to bottom:

atusb-SilkS_Front.gto	Front silk screen
atusb-Mask_Front.gts	Front solder mask
atusb-Front.gtl		Front copper
atusb-Back.gbl		Back copper
atusb-Mask_Back.gbs	Back solder mask


Other design files:

atusb-front.png		Illustration of the PCB's front side
atusb-back.png		idem, for the back side
atusb-PCB_Edges.gbr	Board edges, for routing (Gerber)
atusb.dxf		idem (AutoCAD DXF)
atusb.drl		Excellon drill file
atusb-SoldP_Front.gtp	Front solder paste, for stencil


Interpretation of files:

- for all coordinates, the origin is the lower left corner of the board
- do not print component values on silk screen
- the center (!) of the board edge line marks the true board edge, e.g.,

                             Edge line (5 mil)
                        =======
         ------- - - - - - ----------
               |           |
   PCB outside |           | PCB inside
               |           |
         ------- - - - - - ----------
                     |
               Volume removed when cutting
               (width depends on tool used)
