USB connector for ATUSB production

Werner Almesberger werner at almesberger.net
Wed Mar 30 01:16:43 EDT 2011


[ Taking this from private conversation to the list. ]

I wrote:
> Regarding the space for the USB connector: the connector extends below
> the PCB, so there a) has to be a hole for the connector and b) it should
> have a length of at least 17 mm:
> 
> <17mm->
> +-----+-----------+
> |Hole |-    PCB   |
> |     |-          |
> +-----+-----------+

Here's a picture:
http://downloads.qi-hardware.com/people/werner/wpan/tmp/usb-off-board.jpg

The nominal distance by which the USB connector extends beyond the
PCB edge is 15.2 mm. If we add 0.1 mm of tolerance on the PCB side
and another 0.1 mm for the connector itself, that would be 15.4 mm.
This is also roughly what I measured in my prototypes.

So 17 mm should be a very safe size. In a pinch, we could go as low
as 16 mm. Does the PCB need this in the Gerbers or will they add it
as part of the panelization ?

Plan B would still be to just manually solder the connector. Pro:
- no need to reserve PCB space and make a hole,
- no need to worry about the insertion process,
- may make SMT a little cheaper,
- legs may have stronger solder joints
Contra:
- extra work step,
- board needs cleaning afterwards (flux removal),
- complicates production testing immediately after SMT (we'd
  either need a special test firmware that works without USB and
  then flash the real firmware later, or solder the connector
  before testing)

I asked Adam which of the two connectors he likes better:
 
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=WM17118-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=WM3983CT-ND

His preference was for the one with "cowboy legs", because it's
mechanically stronger. This form factor also seems to be more common
in general.

Note that all of these connectors are designed for boards thicker
than 0.8 mm. It seems that no suitable connectors exist for that
board thickness, so we'll just have to live with this imperfection.

- Werner




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