[gta02-core] Use for hole left by GPS connector - shields

Rask Ingemann Lambertsen ccc94453 at vip.cybercity.dk
Sat Jun 27 19:46:09 CEST 2009

On Fri, Jun 26, 2009 at 10:00:18AM -0300, Werner Almesberger wrote:
> We could make our own shields, but that's a complication I'd
> rather avoid for now.
> I don't know what is involved in making new shields, but 

   I used to work at a place which did shielding solutions based on a
photo-chemical process. To make a shielding can, you cut a sheet[1] of an
appropriate metal to the desired shape and then you bend it.

   Cutting the metal can be done mechanically or by a photo-chemical process
much the same was as the copper pattern on a PCB. Tooling costs (EUR 150000
I've been told) for the mechanical process are unrealistic unless you
produce a few million pieces. The photo-chemical process needs a master
which itself costs only a few hundred EUR; add to that whatever the
photo-chemical shop will charge you for adapting it to their process
equipment. It's more expensive per piece, but definitely the way to go for
prototypes or small to medium production runs.

   Bending the metal pieces into shape is neccesarily a mechanical process.
Again tooling costs is the issue. We'll need to make long contigous bends,
requiring a high force from the press. There's a delicate balance between
making the bends sharp enough to keep the can height down and not cracking
(or even breaking) the material. At the same time, the flat parts need to be
tightly supported to prevent buckles from forming. To me, it doesn't look
like something for which a tool can be done cheaply.

   So if we're considering a new shielding can, I'd say go for an existing
design. For example, Digikey has a product family called "RF shields" in the
category "RF and RFID". They don't appear to ship in bent form, but maybe
shielding cans are available prebent from somewhere else.

[1] or coil

Rask Ingemann Lambertsen
Danish law requires addresses in e-mail to be logged and stored for a year

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