How about a wild departure, an actual electronic design question!

[Dave VanHorn]

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?

 

[ChrisGibboGibson]

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.

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!)

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?

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]

That implies a measurement probem. The volt drop * the current *has* to go
somewhere.

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.

 

[nospam]

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.

=== quote ===
# Will gold plated SIMMs work with my Intel motherboard?

Most Intel motherboards use tin-lead SIMM sockets and Intel recommends NOT
mixing dissimilar metals in your memory solution. Studies show that
fretting occurs when tin comes in pressure contact with gold or any other
metal. Tin debris will transfer to the gold surface and oxidize. Continued
transfer will build up an oxide film layer. Tin surfaces always have a
natural oxide. Despite this, electrical contact is easily made between two
tin surfaces. Oxides on both soft surfaces will bend and break, ensuring
contact. The resistance of the oxidation layer builds up over time when one
surface is hard. Increasing the contact resistance will ultimately result
in memory failures.

Source: Edward Bock, AMP P316-90, Mateability of Tin to Gold, Palladium,
and Silver.
==========

As a kludge try wetting the pins with some WD40 before assembly, I bet it
helps.

 

[artie]

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.

 

[Dave VanHorn]

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.

 

[John Larkin]

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.

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.

Only these pins in the connector are failing.
Yup!


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.

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.

I think gold/tin may be bad news, too.

John

 

[Dave VanHorn]

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.

Yup!

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.

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.

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.

 

[Leon Heller]

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.

[deleted]

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

Leon

 

[Leon Heller]

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.

[deleted]

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

I just did a bit of Googling and AMP doesn't recommend it:

http://www.amp.com/products/technology/sncomrep.pdf

Apparently the tin migrates onto the harder gold and forms tin oxide.

Leon

 

[Tony Williams]

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

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.

 

[YD]

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?

- YD.

 

[N. Thornton]

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.


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.


True, but at this point I don't see why they would heat enough to be a
problem.


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.

It looks to me like youve almost answered your own question. They only
fail when current is consistently high and in auto environment. Whats
the difference?
current heating
vibration
damp
dirt
grit & muck

If other pins are not failing in auto environment, parallelling power
pins is the simplest workaround, though greater contact forces would
be a more rock solid solution.


NT

 

[Dave VanHorn]

It looks to me like youve almost answered your own question.

Almost is the key word..

They only fail when current is consistently high and in auto environment.
Whats
the difference?
current heating

I don't know why this would be different from running on the bench.

vibration

Sitting in a car seat, nothing to write home about.
If they were bolted to the engine block, I'd be worried.

damp

Not really

dirt, grit & muck

None visible, they look like they just came out of the wash at the factory.

If other pins are not failing in auto environment, parallelling power
pins is the simplest workaround, though greater contact forces would
be a more rock solid solution.

Unfortunately, these aren't prototypes.
I need to find out why the contacts are failing, and fix that.

 

[Rich Grise]

Unfortunately, these aren't prototypes.
I need to find out why the contacts are failing, and fix that.

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

 

[Rich Grise]

Cars do tend to vibrate rather a lot. Is it possible that the tin
abrades onto the goldplating and oxidizes there?

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

 

[Steven Swift]

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

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?

 

[Pooh Bear]

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.

Automotive environment = vibration !

Fretting corrosion ?


Graham

 

[Dave VanHorn]

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.

 

[Rich Grise]

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.

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