How about a wild departure, an actual electronic design ques

D

Dave VanHorn

Guest
I'm investigating some field failures.
Unfortunately, the connector manufacturers are gone for the weekend, of
course.

There's a failure happening in a board stacking header, using these two
parts:

Samtec P/N:MMS-112-02-T-DV-LC-K-TR (female, gold)

Samtec P/N:ASP-106552-02 (Custom Dim. based
on the TW Series) Longer pin version of a TW-12-12-T-D-800-090
Male pins, tin.

The board stacking connectors are Samtec pins and sockets, used to stack two
PCBs together.
There is a power connector on the A board, being connected to the B board
through the stacking header.

The power supply is 9-16V at 2.25A from a wall-wart or car lighter plug.
Both sides of this travel through the stacking connector on adjacent pins,
to the B board, where they meet a diode bridge, and go into a switching
supply.

Only these pins in the connector are failing.

When they fail, they go high resistance, so that on the B board, the power
supply measures 2-5V with 15V on the input. No observable heating in this
failure mode.
If the board stack is disturbed, then the connectors "heal" and will work
for some time, minutes or days.

The connector ratings are not defined in terms of a hard limit, rather a
temperature rise over ambient. I know that we have failures where the
ambient did not exceed 40C.

The connectors are shown to have temperature rises by the mfgr's docs:
3A is a 27C rise, in gold, 14 in tin, 2A is 11C in gold and 7 in tin.

We are using the gold version (side note, I'm wondering why the gold is
worse!)

In the end, I would expect something like say 20C rise over 40C ambient,
sitting us at 60C,
Operating temp range is spec'd as -65C to +125C

With the current that I know is flowing here, I just don't see a reason for
failure.
Before I go off looking for ways to get wild current, does anyone see why
these connectors shouldn't handle appx 2A 24/7/365 under these conditions?

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
 
Only these pins in the connector are failing.

When they fail, they go high resistance, so that on the B board, the power
supply measures 2-5V with 15V on the input. No observable heating in this
failure mode.


That implies a measurement probem. The volt drop * the current *has* to go
somewhere.
Click to expand...
The pins go high resistance, so the 2A is no longer flowing, and the drop is
a result of the resistance. That much is perfectly clear.


--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
 
Tin oxide is a tenacious insulator...

A product I was associated with in the past used a similar set of
connectors, tin pins into a plated socket. Thermal cycling moved
things around, and after a while, oxide layers formed on current
carrying pins -- and the product failed.

Recommended field repair technique was to lift the front lip of the
product two inches and let it drop back to the desk. Or, pop the lid
and reseat the board.

Some folks used contact preservatives, which IIRC, seemed to help.

The real fix was to get rid of the tin pins.

--
Namaste--
 
Some new info.

Old systems (made a year ago), not exposed to an automotive environment, do
not exhibit the problem.
New systems (made last week), not exposed to an automotive environment, do
not exhibit the problem.

Both sorts are exhibiting the problem, after being put in an automotive
environment for an unknown period.

The power supply incorporates automotive transient protection.

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
 
2.25 is a lot of amps for a single pin, especially with the same on
its neighbor. It's easy top get an oxidation-based thermal runaway
thing going.
Click to expand...
Check the ratings, Samtec appears to be saying that these are good to 2-3A
at any reasonable temperature.

See also my other note, I was just informed that only units in vehicles are
failing, regardless of age, and that "deskbound" ones are not failing,
regardless of age.

Only these pins in the connector are failing.

Yup!
Click to expand...
Well, these do have the largest current/time product on the connector, but
others carry roughly the same current levels, in pulses of a few seconds
when running.

Don't trust those numbers. The pins heat each other, and may have
local hot spots. I don't run small pins like this above 1 amp, and
prefer lots of power and ground pins in parallel, with equalizing
traces to ensure current sharing if you're really serious.
Click to expand...
True, but at this point I don't see why they would heat enough to be a
problem.

I think gold/tin may be bad news, too.
Click to expand...
It must also take current, and maybe something else, because we aren't
getting these failures on the other pins of the same connector. 24 pins
total.

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
 
"Dave VanHorn" <dvanhorn@cedar.net> wrote in message
news:1LednRLIv4FF8e3cRVn-sg@comcast.com...
I'm investigating some field failures.
Unfortunately, the connector manufacturers are gone for the weekend, of
course.

There's a failure happening in a board stacking header, using these two
parts:

Samtec P/N:MMS-112-02-T-DV-LC-K-TR (female, gold)

Samtec P/N:ASP-106552-02 (Custom Dim. based
on the TW Series) Longer pin version of a TW-12-12-T-D-800-090
Male pins, tin.

The board stacking connectors are Samtec pins and sockets, used to stack
two PCBs together.
There is a power connector on the A board, being connected to the B board
through the stacking header.
Click to expand...
[deleted]

Should you be using gold on one and tin on the other? I vaguely remember
seeing somewhere that it can cause problems.

Leon
 
In article <4170eb2e$0$2273$cc9e4d1f@news-text.dial.pipex.com>,
Leon Heller <leon_heller@hotmail.com> wrote:

Should you be using gold on one and tin on the other? I vaguely
remember seeing somewhere that it can cause problems.
Click to expand...
Yes, dissimilar metals in contact with each other can be
a source of contact problems, especially if there is a
hint of moisture around. I even call up tinned sockets
for dil integrated circuits, and avoid the more 'respectable'
gold plated turned pin sockets.

--
Tony Williams.
 
On Sat, 16 Oct 2004 03:08:58 -0500, "Dave VanHorn"
<dvanhorn@cedar.net> wrote:

2.25 is a lot of amps for a single pin, especially with the same on
its neighbor. It's easy top get an oxidation-based thermal runaway
thing going.

Check the ratings, Samtec appears to be saying that these are good to 2-3A
at any reasonable temperature.

See also my other note, I was just informed that only units in vehicles are
failing, regardless of age, and that "deskbound" ones are not failing,
regardless of age.
Click to expand...
Cars do tend to vibrate rather a lot. Is it possible that the tin
abrades onto the goldplating and oxidizes there?

- YD.

--
Remove HAT if replying by mail.
 
On Sat, 16 Oct 2004 12:29:07 -0500, Dave VanHorn wrote:
Unfortunately, these aren't prototypes.
I need to find out why the contacts are failing, and fix that.
Click to expand...
It's the gold pins in tin sockets. Or tin pins in gold sockets.
Change one or the other, and when one fails in the field, replace
it with one with proper mating connectors. And eat the cost as
tuition in the school of hard knocks. :)

Cheers!
Rich
 
On Sat, 16 Oct 2004 10:42:24 -0300, YD wrote:

On Sat, 16 Oct 2004 03:08:58 -0500, "Dave VanHorn"
dvanhorn@cedar.net> wrote:

2.25 is a lot of amps for a single pin, especially with the same on
its neighbor. It's easy top get an oxidation-based thermal runaway
thing going.

Check the ratings, Samtec appears to be saying that these are good to 2-3A
at any reasonable temperature.

See also my other note, I was just informed that only units in vehicles are
failing, regardless of age, and that "deskbound" ones are not failing,
regardless of age.


Cars do tend to vibrate rather a lot. Is it possible that the tin
abrades onto the goldplating and oxidizes there?
Click to expand...
Yes, four or five people have posted that it does. With tin/tin, the
tin oxide flakes off and leaves soft tin to soft tin. Gold/gold, there's
no oxide, just all gold. Gold/tin, there's gold, tin oxide, and tin,
and when the tin oxide flakes off the tin, it embeds itself into the
surface of the gold, like a little mosaic insulation layer.

Change one or the other, it's that simple.

Cheers!
Rich
 
Sounds like "fretting corrosion." You CANNOT mix tin and gold, that is
much worse than tin-tin or gold to gold.


"Dave VanHorn" <dvanhorn@cedar.net> writes:


I'm investigating some field failures.
Unfortunately, the connector manufacturers are gone for the weekend, of
course.

There's a failure happening in a board stacking header, using these two
parts:

Samtec P/N:MMS-112-02-T-DV-LC-K-TR (female, gold)

Samtec P/N:ASP-106552-02 (Custom Dim. based
on the TW Series) Longer pin version of a TW-12-12-T-D-800-090
Male pins, tin.

The board stacking connectors are Samtec pins and sockets, used to stack two
PCBs together.
There is a power connector on the A board, being connected to the B board
through the stacking header.

The power supply is 9-16V at 2.25A from a wall-wart or car lighter plug.
Both sides of this travel through the stacking connector on adjacent pins,
to the B board, where they meet a diode bridge, and go into a switching
supply.

Only these pins in the connector are failing.

When they fail, they go high resistance, so that on the B board, the power
supply measures 2-5V with 15V on the input. No observable heating in this
failure mode.
If the board stack is disturbed, then the connectors "heal" and will work
for some time, minutes or days.

The connector ratings are not defined in terms of a hard limit, rather a
temperature rise over ambient. I know that we have failures where the
ambient did not exceed 40C.

The connectors are shown to have temperature rises by the mfgr's docs:
3A is a 27C rise, in gold, 14 in tin, 2A is 11C in gold and 7 in tin.

We are using the gold version (side note, I'm wondering why the gold is
worse!)

In the end, I would expect something like say 20C rise over 40C ambient,
sitting us at 60C,
Operating temp range is spec'd as -65C to +125C

With the current that I know is flowing here, I just don't see a reason for
failure.
Before I go off looking for ways to get wild current, does anyone see why
these connectors shouldn't handle appx 2A 24/7/365 under these conditions?

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
Click to expand...

--
Steven D. Swift, novatech@eskimo.com, http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA
 
Dave VanHorn wrote:

Some new info.

Old systems (made a year ago), not exposed to an automotive environment, do
not exhibit the problem.
New systems (made last week), not exposed to an automotive environment, do
not exhibit the problem.

Both sorts are exhibiting the problem, after being put in an automotive
environment for an unknown period.

The power supply incorporates automotive transient protection.
Click to expand...
Automotive environment = vibration !

Fretting corrosion ?


Graham
 
So the other 22 identical pins in the same connector are somehow immune?

There are eight pins that carry high current in this connector, two are
failing.
They are both on the input supply.

Something else is happening.

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
 
On Sat, 16 Oct 2004 20:28:16 -0500, Dave VanHorn wrote:

So the other 22 identical pins in the same connector are somehow immune?

There are eight pins that carry high current in this connector, two are
failing.
They are both on the input supply.

Something else is happening.
Click to expand...
Maybe so, but you won't be able to isolate it until you remove one
of the KNOWN causes of a malfunction while continuing to troubleshoot.

The tin-gold contact in the connectors is the problem, and will
continue to be a problem through the life of the product, i.e.
forever, unless a different part is specified.

The only reason you haven't seen the rest of the pins fail yet is
because the two that do fail always fail first. Jostling the
connector or whatever you're doing rewipes all the contacts, so
you never see the other pins fail.

Until you respec that connector, it will never work right, and you will
continue to bark up the same wrong tree.

Good Luck!
Rich
 
Never mind, The Gold Tin interface is the problem. It's sometimes referred
to as the "purple plague". Vibrations and environmental changes can
aggravate this, such as high humidity, and temperature.

http://www.google.ca/search?hl=en&ie=ISO-8859-1&q=purple+plague+gold+tin&met
a=



"Jeff" <levy_jeff@hotmail.com> wrote in message
news:jdwcd.149344$Np3.6454734@ursa-nb00s0.nbnet.nb.ca...
You said something about transient protection - is this in the circuit
before or after the pins?


"Dave VanHorn" <dvanhorn@cedar.net> wrote in message
news:1LednRLIv4FF8e3cRVn-sg@comcast.com...

I'm investigating some field failures.
Unfortunately, the connector manufacturers are gone for the weekend, of
course.

There's a failure happening in a board stacking header, using these two
parts:

Samtec P/N:MMS-112-02-T-DV-LC-K-TR (female, gold)

Samtec P/N:ASP-106552-02 (Custom Dim. based
on the TW Series) Longer pin version of a TW-12-12-T-D-800-090
Male pins, tin.

The board stacking connectors are Samtec pins and sockets, used to stack
two
PCBs together.
There is a power connector on the A board, being connected to the B
board
through the stacking header.

The power supply is 9-16V at 2.25A from a wall-wart or car lighter plug.
Both sides of this travel through the stacking connector on adjacent
pins,
to the B board, where they meet a diode bridge, and go into a switching
supply.

Only these pins in the connector are failing.

When they fail, they go high resistance, so that on the B board, the
power
supply measures 2-5V with 15V on the input. No observable heating in
this
failure mode.
If the board stack is disturbed, then the connectors "heal" and will
work
for some time, minutes or days.

The connector ratings are not defined in terms of a hard limit, rather a
temperature rise over ambient. I know that we have failures where the
ambient did not exceed 40C.

The connectors are shown to have temperature rises by the mfgr's docs:
3A is a 27C rise, in gold, 14 in tin, 2A is 11C in gold and 7 in tin.

We are using the gold version (side note, I'm wondering why the gold is
worse!)

In the end, I would expect something like say 20C rise over 40C ambient,
sitting us at 60C,
Operating temp range is spec'd as -65C to +125C

With the current that I know is flowing here, I just don't see a reason
for
failure.
Before I go off looking for ways to get wild current, does anyone see
why
these connectors shouldn't handle appx 2A 24/7/365 under these
conditions?

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
Click to expand...
 
You said something about transient protection - is this in the circuit
before or after the pins?
Click to expand...
It's after the pins, but that's not the problem. See my other message.
It's been a LONG weekend..

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
 
"Dave VanHorn" wrote:

I'm investigating some field failures.
Unfortunately, the connector manufacturers are gone for the weekend, of
course.

There's a failure happening in a board stacking header, using these two
parts:

Samtec P/N:MMS-112-02-T-DV-LC-K-TR (female, gold)

Samtec P/N:ASP-106552-02 (Custom Dim. based
on the TW Series) Longer pin version of a TW-12-12-T-D-800-090
Male pins, tin.

The board stacking connectors are Samtec pins and sockets, used to stack two
PCBs together.
There is a power connector on the A board, being connected to the B board
through the stacking header.

The power supply is 9-16V at 2.25A from a wall-wart or car lighter plug.
Both sides of this travel through the stacking connector on adjacent pins,
to the B board, where they meet a diode bridge, and go into a switching
supply.

Only these pins in the connector are failing.

When they fail, they go high resistance, so that on the B board, the power
supply measures 2-5V with 15V on the input. No observable heating in this
failure mode.
Click to expand...
That implies a measurement probem. The volt drop * the current *has* to go
somewhere.

If the board stack is disturbed, then the connectors "heal" and will work
for some time, minutes or days.

The connector ratings are not defined in terms of a hard limit, rather a
temperature rise over ambient. I know that we have failures where the
ambient did not exceed 40C.

The connectors are shown to have temperature rises by the mfgr's docs:
3A is a 27C rise, in gold, 14 in tin, 2A is 11C in gold and 7 in tin.

We are using the gold version (side note, I'm wondering why the gold is
worse!)
Click to expand...
I'm wondering more than you are.

In the end, I would expect something like say 20C rise over 40C ambient,
sitting us at 60C,
Operating temp range is spec'd as -65C to +125C

With the current that I know is flowing here, I just don't see a reason for
failure.
Before I go off looking for ways to get wild current, does anyone see why
these connectors shouldn't handle appx 2A 24/7/365 under these conditions?
Click to expand...
I know what you're thinking. And I'm inclined to agree. Serious
mis-measurements or intermittent currents that you haven't seen.

Gibbo
 
"Dave VanHorn" <dvanhorn@cedar.net> schreef in bericht
news:4JadnUNdzdcDV-zcRVn-uw@comcast.com...
So the other 22 identical pins in the same connector are somehow immune?

There are eight pins that carry high current in this connector, two are
failing.
They are both on the input supply.

Something else is happening.
Click to expand...
Assemble with (plenty) acid-free vaselin grease.

--
Thanks, Frank.
(remove 'x' and 'invalid' when replying by email)
 
You said something about transient protection - is this in the circuit
before or after the pins?


"Dave VanHorn" <dvanhorn@cedar.net> wrote in message
news:1LednRLIv4FF8e3cRVn-sg@comcast.com...
I'm investigating some field failures.
Unfortunately, the connector manufacturers are gone for the weekend, of
course.

There's a failure happening in a board stacking header, using these two
parts:

Samtec P/N:MMS-112-02-T-DV-LC-K-TR (female, gold)

Samtec P/N:ASP-106552-02 (Custom Dim. based
on the TW Series) Longer pin version of a TW-12-12-T-D-800-090
Male pins, tin.

The board stacking connectors are Samtec pins and sockets, used to stack
two
PCBs together.
There is a power connector on the A board, being connected to the B board
through the stacking header.

The power supply is 9-16V at 2.25A from a wall-wart or car lighter plug.
Both sides of this travel through the stacking connector on adjacent pins,
to the B board, where they meet a diode bridge, and go into a switching
supply.

Only these pins in the connector are failing.

When they fail, they go high resistance, so that on the B board, the power
supply measures 2-5V with 15V on the input. No observable heating in this
failure mode.
If the board stack is disturbed, then the connectors "heal" and will work
for some time, minutes or days.

The connector ratings are not defined in terms of a hard limit, rather a
temperature rise over ambient. I know that we have failures where the
ambient did not exceed 40C.

The connectors are shown to have temperature rises by the mfgr's docs:
3A is a 27C rise, in gold, 14 in tin, 2A is 11C in gold and 7 in tin.

We are using the gold version (side note, I'm wondering why the gold is
worse!)

In the end, I would expect something like say 20C rise over 40C ambient,
sitting us at 60C,
Operating temp range is spec'd as -65C to +125C

With the current that I know is flowing here, I just don't see a reason
for
failure.
Before I go off looking for ways to get wild current, does anyone see why
these connectors shouldn't handle appx 2A 24/7/365 under these conditions?

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR
Click to expand...
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top