[gta02-core] New shields

Werner Almesberger werner at openmoko.org
Tue Sep 1 21:52:10 CEST 2009

Rask Ingemann Lambertsen wrote:
>    One thing I had in mind was to find out which shields they already make
> that could be used. Having a list of shields that we could just order 20 of
> would be nice.

Hmm, if you look at GTA02, all shields are specifically designed for
the shape of the device. Only the "outer" WLAN shield may be a
generic shape.

Even if we assume all possible rectangular shapes are available,
you'd still have massive size losses, e.g.,

- main can: 31 mm x 49 mm, with a corner of about 9 mm x 14 mm.
  So we get 31*49 = 1519 mm2 vs. (31-9)*49 = 1078 mm2 or 31*(49-14) =
  1085 mm2. That's a loss of about 30% of the surface.

- GPS: 15 mm x 20 mm, minus 9 mm x 14 mm (same as main can).
  Thus, 15*20 = 300 mm2 vs. (15-9)*20 = 120 mm2 or 15*(20-14) =
  90 mm2. A whopping 60% surface decrease. And you need to cut the
  holes for surface traces.

So I don't see this as a promising approach for gta02-core. It may
be a choice for a completely new design with a new case, but even
there the cost of having available can sizes drive the design seems

So I'd rather know if making one's own shields for prototypes is
truly so terribly difficult, and how bad custom-made shields are for

At Openmoko, I heard some grumbling about the removable shields,
and SMT'ing shields wasn't fun either (pick and place doesn't seem
to like them, you can't see easily if they touch something, and
they're big so there's a lot of things they might touch), but
besides that, I don't remember them being mentioned as a major

- Werner

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