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From: D Yuniskis on 20 Jan 2010 03:13
Hi,

I don't like using sockets in products. They add to
cost, decrease reliability, tempt customers to "play"
with the device(s) in those socket(s), etc. So, most
of the things I work on simply can't tolerate them
(either for reliability or "regulatory" requirements).

But, the sockets I *have* used in the past have always
been for *components* that would otherwise be soldered
onto the PCB. And, were of high enough quality that
I didn't fear the socket+device failing.

I'm now thinking about putting "consumer" flash memory
devices in a design in lieu of equivalent components
soldered onto the PCB. E.g., mount an SD socket and
use an SD *module* (or other media choices).

The point is, this is done AS IF it was a permanently
attached device. I.e., imagine fab'ing the board,
slipping an SD card into the socket, and then encasing
the entire assembly in a sealed box (so the SD card is
socketed yet never removed).

But, I'm not sure that these types of sockets are
really intended for this type of long term use.
I.e., do they *expect* frequent insertions and removals
to wipe the contacts clean periodically?

Anyone with any experience in this regard? And, any
preferences to a particular technology that would be
least likely to cause problems when used this way?
(not sure what criteria would need to be maximized,
there).

Thanks!
--don
From: news on 20 Jan 2010 04:49
In article <hj6dcs$3st$1(a)speranza.aioe.org>, not.going.to.be(a)seen.com
says...
> Hi,
>
> I don't like using sockets in products. They add to
> cost, decrease reliability, tempt customers to "play"
> with the device(s) in those socket(s), etc. So, most
> of the things I work on simply can't tolerate them
> (either for reliability or "regulatory" requirements).
>
> But, the sockets I *have* used in the past have always
> been for *components* that would otherwise be soldered
> onto the PCB. And, were of high enough quality that
> I didn't fear the socket+device failing.
>
> I'm now thinking about putting "consumer" flash memory
> devices in a design in lieu of equivalent components
> soldered onto the PCB. E.g., mount an SD socket and
> use an SD *module* (or other media choices).
>
> The point is, this is done AS IF it was a permanently
> attached device. I.e., imagine fab'ing the board,
> slipping an SD card into the socket, and then encasing
> the entire assembly in a sealed box (so the SD card is
> socketed yet never removed).
>
> But, I'm not sure that these types of sockets are
> really intended for this type of long term use.
> I.e., do they *expect* frequent insertions and removals
> to wipe the contacts clean periodically?
>
> Anyone with any experience in this regard? And, any
> preferences to a particular technology that would be
> least likely to cause problems when used this way?
> (not sure what criteria would need to be maximized,
> there).
>
> Thanks!
> --don

We have just done exactly this - micro-SD card in a socket on the board,
to hold calibration data.
The card and socket contacts are both gold-plated, so I'm not expecting
any problems. Other contact materials, I'd be a bit wary.

Lots of embedded-PC-based systems (including ours) boot from a Compact
Flash card. These usually have gold-plated contacts on both sides; our
oldest machines have been in the field for about 5 years with no
problems in this area.

HTH
From: Vladimir Vassilevsky on 20 Jan 2010 10:00


D Yuniskis wrote:
> Hi,
>
> I don't like using sockets in products. They add to
> cost, decrease reliability, tempt customers to "play"
> with the device(s) in those socket(s), etc.

Very true.

> I'm now thinking about putting "consumer" flash memory
> devices in a design in lieu of equivalent components
> soldered onto the PCB. E.g., mount an SD socket and
> use an SD *module* (or other media choices).
>
> The point is, this is done AS IF it was a permanently
> attached device. I.e., imagine fab'ing the board,
> slipping an SD card into the socket, and then encasing
> the entire assembly in a sealed box (so the SD card is
> socketed yet never removed).

> Anyone with any experience in this regard?

Once we did exactly that for an industrial device. Even if you secure
the card and socket with additional straps, the socket + card assy
remains one of the least reliable places. It is also prone to
manufacturing problems, such as loose soldering. So, in the next
revisions of the project we changed to the bare NAND flash soldered
directly on the board, and that was heck of a lot better.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
From: Tim Wescott on 20 Jan 2010 11:33
On Wed, 20 Jan 2010 09:00:26 -0600, Vladimir Vassilevsky wrote:

> D Yuniskis wrote:
>> Hi,
>>
>> I don't like using sockets in products. They add to cost, decrease
>> reliability, tempt customers to "play" with the device(s) in those
>> socket(s), etc.
>
> Very true.
>
>> I'm now thinking about putting "consumer" flash memory devices in a
>> design in lieu of equivalent components soldered onto the PCB. E.g.,
>> mount an SD socket and use an SD *module* (or other media choices).
>>
>> The point is, this is done AS IF it was a permanently attached device.
>> I.e., imagine fab'ing the board, slipping an SD card into the socket,
>> and then encasing the entire assembly in a sealed box (so the SD card
>> is socketed yet never removed).
>
>> Anyone with any experience in this regard?
>
> Once we did exactly that for an industrial device. Even if you secure
> the card and socket with additional straps, the socket + card assy
> remains one of the least reliable places. It is also prone to
> manufacturing problems, such as loose soldering. So, in the next
> revisions of the project we changed to the bare NAND flash soldered
> directly on the board, and that was heck of a lot better.
>
Several years ago I was working on a product that looked like it was
going to need a NAND. We didn't go down that path, but I looked into
things long enough to know that there didn't seem to be any commercial
solutions to using NAND in all it's glory, and worse there weren't even
white papers (in English, at least) that detailed any manufacturer's
recommendations on using the redundant bits for error checking and
correction.

Has that changed? Did you use the redundant bits for FEC or did you
ignore them ore use them for other things? Did you roll your own
solution, or did you find something off the shelf?

--
www.wescottdesign.com
From: larwe on 20 Jan 2010 11:45
On Jan 20, 11:33 am, Tim Wescott <t...(a)seemywebsite.com> wrote:



> things long enough to know that there didn't seem to be any commercial
> solutions to using NAND in all it's glory, and worse there weren't even
> white papers (in English, at least) that detailed any manufacturer's
> recommendations on using the redundant bits for error checking and
> correction.

Not exactly true, there's the SSFDC specification (thank God that's
dead). Since an SSFDC is just an encapsulated, ESD-protected NAND
chip, it was handy in our products to have a SSFDC socket as well as a
soldered NAND chip - and a switch to toggle the select lines. Flip one
way, we boot off internal NAND; the other way, we boot off the SSFDC
card. Great for development (no JTAG on the processor, and no ICE
available - it was burn and pray).

Nowadays we have the MTD drivers in Linux, at least. Lots of buyware
solutions too. You'd have to be out of your mind to roll your own FS
and physical sector handler code these days.

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