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From: Vladimir Vassilevsky on 20 Jan 2010 14:58


D Yuniskis wrote:

> Hi Vladimir,
>
> Vladimir Vassilevsky wrote:
>
>> D Yuniskis wrote:
>>
>>> I'm now thinking about putting "consumer" flash memory
>>> devices in a design in lieu of equivalent components
>>> soldered onto the PCB.
>>> 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
>
>
> Which technology did you use?

Compact Flash.

> I.e., I would expect SD and SM
> to have different issues as a consequence of their physical
> characteristics.

BTW, there is a considerable difference in the reliability of the cards
depending on particular make.

> How was the "media card" used by the application?

Cards were used for raw data storage. Hundreds of files, gigabytes of
data, sustained write ~several MB/sec. Environmental: shock and
vibration, temperature variations. Unsupervised operation in outdoor
conditions.

I.e.,
> *booting* off it but otherwise executing out of RAM places
> infrequent demands on it. OTOH, using it in a datalogger
> would place *continuous* demands on it.

Yes.

> Did you use any special selection criteria when picking the
> socket? Or, just some run-of-the-mill part for consumer
> devices?

Tried several TH and SMT sockets, looking for best quality of contacts
and overall mechanical robustness.

>> the card and socket with additional straps, the socket + card assy
>> remains one of the least reliable places. It is also prone to
>
>
> Yes. But, what sorts of failures did you encounter? Problems
> because folks "played" with the parts (because they *looked*
> like they were removable)? Failures of the connections over
> time (oxidation, biological agents, etc.)? Intermittent
> due to things like vibration?

Random problems in connection card<->socket and socket<->board.
Cured by replacement of card and socket.

>> we changed to the bare NAND flash soldered
>> directly on the board, and that was heck of a lot better.
>
>
> That's what I would expect. Though I'm not sure how to put
> a "figure" on "heck of a lot better".

Card failure was one of the common problems; no such issue with ICs
soldered on the board.

:< Removable media
> offers some advantages (i.e., it can be replaced/upgraded
> over time so you don't end up replacing the entire device)

Removable media works fine for tabletop conditions; however it is
difficult to design a removable media that should work reliably in the
field.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
From: Robert Baer on 20 Jan 2010 17:49
news(a)rblack01.plus.com wrote:
> 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
Check.
Solder "plating" on PCB fingers and tin socket contacts last roughly
2 years before a likely failure - which can be fixed by unplugging and
re-insertion.
From: Theo Markettos on 20 Jan 2010 18:28
In comp.arch.embedded news(a)rblack01.plus.com wrote:
> 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.

One of the new Freescale ARM CPUs has an SD interface for flash, and enough
logic in it to be able to boot from SD. So you can have (micro) SD as the
only nonvolatile storage on the board.

I know one consumer device (the Chumby One) that does just this. It has
hidden microSD inside - accessible if you unscrew it from the board, but
otherwise intended to be hidden (the idea is easier user fixing of
problems... brick your box? Just pop the firmware card in a Linux box and
run 'dd')

Theo
From: Adrian C on 20 Jan 2010 19:28
On 20/01/2010 23:28, Theo Markettos wrote:
>
> I know one consumer device (the Chumby One) that does just this. It has
> hidden microSD inside - accessible if you unscrew it from the board, but
> otherwise intended to be hidden (the idea is easier user fixing of
> problems... brick your box? Just pop the firmware card in a Linux box and
> run 'dd')

http://www.ifixit.com/Teardown/chumby-one/1614/1

--
Adrian C
From: D Yuniskis on 20 Jan 2010 19:49
Hi Vladimir,

[attributions elided]

>>> Once we did exactly that for an industrial device. Even if you secure
>>
>> Which technology did you use?
>
> Compact Flash.

Wow! And you had problems with that? I would have thought the CF
connector to be more reliable than SD, MS, SM, etc. Though CF's
tend to also be more massive which might make vibration more of
an issue...

>> How was the "media card" used by the application?
>
> Cards were used for raw data storage. Hundreds of files, gigabytes of
> data, sustained write ~several MB/sec. Environmental: shock and
> vibration, temperature variations. Unsupervised operation in outdoor
> conditions.

So a pretty hostile environment? I might be able to win, there,
as these *should* see nothing more than temperature extremes
(~60C ambient). If I open source the design, then folks may
actually *welcome* the "memory card" approach. :-/ I'll
have to think hard about the consequences for *my* uses...

>> Did you use any special selection criteria when picking the
>> socket? Or, just some run-of-the-mill part for consumer
>> devices?
>
> Tried several TH and SMT sockets, looking for best quality of contacts
> and overall mechanical robustness.

But, this was a datalogger so the card was (frequently?) removed
and reinserted (?). I.e., what if it had been plugged and left?

>> Yes. But, what sorts of failures did you encounter? Problems
>> because folks "played" with the parts (because they *looked*
>> like they were removable)? Failures of the connections over
>> time (oxidation, biological agents, etc.)? Intermittent
>> due to things like vibration?
>
> Random problems in connection card<->socket and socket<->board.
> Cured by replacement of card and socket.

And this wasn't related to insertion/removal fatigue?

> :< Removable media
>> offers some advantages (i.e., it can be replaced/upgraded
>> over time so you don't end up replacing the entire device)
>
> Removable media works fine for tabletop conditions; however it is
> difficult to design a removable media that should work reliably in the
> field.
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