Chip failure and air corrossion products

[N_Cook]

Anyone any insight on this. Failure of 34 year old TTL chip, in
unpowered storage. Just 1 of 50 chips on a board, TTL,4000, analogue,
memory etc.
Only this one had silver tarnish looking appearance of black silver
sulphide on the pins. This make of TTL did for a while have silver
plating aded to the pin frame , for a period.
I cracked open the device and no obvious tarnish on internal frame
metal. Anyone know what the failure process was? was silver plating
found to be problematic?

 

[pfjw@aol.com]

Most silver plating is "fine" silver. And proper plating is quite complex starting with a copper layer, then the silver layer. Back in the day when coal was the main fuel of choice, and there was no differentiation between high and low sulphur coal, plate-silver used to tarnish (not corrode) quickly due to high levels of SO2 in the air. Hence the references in Victorian times to "polishing the silver" as a full time job. Also back in the day, the underlying materials were often brass or bronze, so quite stable in itself.. Further, electroplating was not yet an established science so "plate" was made using a dipping process with sterling silver. Sterling silver is far more prone to tarnish than fine silver, and, why the 'very best' plate used fine-silver for surfaces exposed to food or drink. It does not tarnish under normal conditions.

Today, the underlying materials might be anything from steel to brass to copper to many other things. The copper layer is still necessary for the silver to adhere, and the silver coating will be the minimum amount absolutely necessary. The silver will be fine silver from this method and very resistant to tarnish.

So, here is what happens. As the plating ages, especially if there are heat/cool cycles, the silver coating will get tiny holes - right through the copper to the base material. Now, electrolysis can occur as O2 and moisture gets between the copper and the base material. This causes tiny flaking (granular) such as you describe. At this point, the silver actually makes things worse by using the copper as a sacrificial electrode.

At home, take a common nail and a bit of copper wire. Wrap the wire around the nail and drop both into a glass of tap water. Give it a week.

If you have a bit of silver wire (must be fine silver), do the same with both wrapped around the nail.

Peter Wieck
Melrose Park, PA

 

[N_Cook]

On 03/03/2017 08:36, N_Cook wrote:

Anyone any insight on this. Failure of 34 year old TTL chip, in
unpowered storage. Just 1 of 50 chips on a board, TTL,4000, analogue,
memory etc.
Only this one had silver tarnish looking appearance of black silver
sulphide on the pins. This make of TTL did for a while have silver
plating aded to the pin frame , for a period.
I cracked open the device and no obvious tarnish on internal frame
metal. Anyone know what the failure process was? was silver plating
found to be problematic?

Silver tarnish appearance of that sort of granular/cellular/mottling
effect of silver tarnish rather than the very black soot-like appearance
of CuS.

 

[pfjw@aol.com]

a) Silver Oxide will not form in this case, as copper is sacrificial to silver.
b) Copper Oxide (Cu0) is a semi-conductor, and is also black as described, and under the condition described would have looked like soot. But, as a semi-conductor would have led to all kinds of erratic behavior.

But, that does not take away from your correct conclusion that it would have been enough (for now) just to clean. However, as long as there was now-exposed copper, the process would have continued until all the copper was consumed. By then, all the silver would have been dissipated as well.

Peter Wieck
Melrose Park, PA

 

[pfjw@aol.com]

On Friday, March 3, 2017 at 1:21:14 PM UTC-5, N_Cook wrote:

All this is one the external sections of the pins? how would these
effects progress into the active die or at least weld-spots ?
This piece of kit was not stored i na damp environment, so no chance of
capilliary action.

This is all happening at the chemical level by electrolysis. So the corrosion would follow the path as the copper starts being exposed. Clearly the silver-over-copper extends into the body of the die - and the same oxides would form within. Once the process is established, no moisture is really necessary, just oxygen and time. You have to understand that the galvanic action is made much worse by the presence of silver making copper act as a sacrificial electrode to the silver reacting with anything attacking it and whatever the base metal might be.

The thickness of the coating - at least several molecules - is plenty wide enough, if you will excuse the expression.

Peter Wieck
Melrose Park, PA

 

[pfjw@aol.com]

Mpfffff..... Some clarification required.

FINE silver plating (most of it) *will not* tarnish from exposure to air, nor will it form sulphur compounds - without other contributing factors. Sterling silver (.925 silver) is an entirely different matter.

What is going on here electro-galvanic (galvanic action) *corrosion* of the copper plating under the silver - and most things electro-silver-plated other than brass are first copper-plated to guarantee proper adhesion.

The black material noted is CuO, not tarnished silver.

Peter Wieck
Melrose Park, PA

 

[pfjw@aol.com]

On Friday, March 3, 2017 at 3:51:17 PM UTC-5, John Robertson wrote:

Thanks, we've had many an Eprom with corroded legs that are from the
70s, in some cases the legs break off inside the IC sockets when the
EPROM is removed. Also this is common on some other ICs used in the
early 80s, such as Galaga which has Namco custom ICs, where again the
legs are corroding right off them.

Is there any way to arrest the process? Be nice to have something to dip
the legs into to cancel the corrosion, similar to using white vinegar
and water (50/50) to neutralize alkaline battery leakage corrosion.

John :-#)#

The best way I have found - if at all possible - is a coat of flexible lacquer over the entirety. I admit to having a bottle of flexible fingernail polish hidden away amongst my other solvents for this sort of thing. Stop the air, stop the corrosion.

Peter Wieck
Melrose Park, PA

 

[pfjw@aol.com]

Yep. "Elephant Snot" turned out to be a very bad idea over time. Much like foam speaker surrounds of recent memory.

I use an acid-free neutral-formula flexible hot-melt for the purpose. I source from AdTech.

Peter Wieck
Melrose Park, PA

 

[Sjouke Burry]

On 03.03.17 9:36, N_Cook wrote:

Anyone any insight on this. Failure of 34 year old TTL chip, in
unpowered storage. Just 1 of 50 chips on a board, TTL,4000, analogue,
memory etc.
Only this one had silver tarnish looking appearance of black silver
sulphide on the pins. This make of TTL did for a while have silver
plating aded to the pin frame , for a period.
I cracked open the device and no obvious tarnish on internal frame
metal. Anyone know what the failure process was? was silver plating
found to be problematic?

Silver oxide conducts.
So, it could have been enough to clean to body of the ttl chip.

 

[N_Cook]

On 03/03/2017 17:41, pfjw@aol.com wrote:

a) Silver Oxide will not form in this case, as copper is sacrificial to silver.
b) Copper Oxide (Cu0) is a semi-conductor, and is also black as described, and under the condition described would have looked like soot. But, as a semi-conductor would have led to all kinds of erratic behavior.

But, that does not take away from your correct conclusion that it would have been enough (for now) just to clean. However, as long as there was now-exposed copper, the process would have continued until all the copper was consumed. By then, all the silver would have been dissipated as well.

Peter Wieck
Melrose Park, PA

All this is one the external sections of the pins? how would these
effects progress into the active die or at least weld-spots ?
This piece of kit was not stored i na damp environment, so no chance of
capilliary action.

 

[Benderthe.evilrobot]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news9b9r3$71c$1@dont-email.me...

Anyone any insight on this. Failure of 34 year old TTL chip, in unpowered
storage. Just 1 of 50 chips on a board, TTL,4000, analogue, memory etc.
Only this one had silver tarnish looking appearance of black silver
sulphide on the pins. This make of TTL did for a while have silver plating
aded to the pin frame , for a period.
I cracked open the device and no obvious tarnish on internal frame metal.
Anyone know what the failure process was? was silver plating found to be
problematic?

There have been problems in the past where gold plated IC pins have
developed a microscopic insulating layer - but I don't know about silver
plated.

Silver plating develops black silver sulphide after long exposure to air,
with NOS parts you'd just clean it off and solder as normal. Silver is a
component of several types of solder alloys. So I don't think it should
cause any problems.

 

[John Robertson]

On 2017/03/03 12:28 PM, pfjw@aol.com wrote:

Mpfffff..... Some clarification required.

FINE silver plating (most of it) *will not* tarnish from exposure to air, nor will it form sulphur compounds - without other contributing factors. Sterling silver (.925 silver) is an entirely different matter.

What is going on here electro-galvanic (galvanic action) *corrosion* of the copper plating under the silver - and most things electro-silver-plated other than brass are first copper-plated to guarantee proper adhesion.

The black material noted is CuO, not tarnished silver.

Peter Wieck
Melrose Park, PA

Thanks, we've had many an Eprom with corroded legs that are from the
70s, in some cases the legs break off inside the IC sockets when the
EPROM is removed. Also this is common on some other ICs used in the
early 80s, such as Galaga which has Namco custom ICs, where again the
legs are corroding right off them.

Is there any way to arrest the process? Be nice to have something to dip
the legs into to cancel the corrosion, similar to using white vinegar
and water (50/50) to neutralize alkaline battery leakage corrosion.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[Benderthe.evilrobot]

"John Robertson" <spam@flippers.com> wrote in message
news:J_OdnT_d4oCiSiTFnZ2dnUU7-fHNnZ2d@giganews.com...

On 2017/03/03 12:28 PM, pfjw@aol.com wrote:
Mpfffff..... Some clarification required.

FINE silver plating (most of it) *will not* tarnish from exposure to air,
nor will it form sulphur compounds - without other contributing factors.
Sterling silver (.925 silver) is an entirely different matter.

What is going on here electro-galvanic (galvanic action) *corrosion* of
the copper plating under the silver - and most things
electro-silver-plated other than brass are first copper-plated to
guarantee proper adhesion.

The black material noted is CuO, not tarnished silver.

Peter Wieck
Melrose Park, PA


Thanks, we've had many an Eprom with corroded legs that are from the 70s,
in some cases the legs break off inside the IC sockets when the EPROM is
removed. Also this is common on some other ICs used in the early 80s, such
as Galaga which has Namco custom ICs, where again the legs are corroding
right off them.

Is there any way to arrest the process? Be nice to have something to dip
the legs into to cancel the corrosion, similar to using white vinegar and
water (50/50) to neutralize alkaline battery leakage corrosion.

No idea whether its related - but when I serviced VGA monitors, I often
encountered brown glue that was probably applied to prevent components from
fatiguing their leads.

This stuff eventually became brittle and crumbly - and highly corrosive. It
frequently etched away component leads.

Once brittle it was fairly easy to chip away, but in the early stages it was
elastic like contact adhesive, and lighter brown like Evo-stik.

Very often a component like a resistor would come out encased in this stuff
and the leads completely eaten away.

 

[N_Cook]

On 03/03/2017 21:08, Benderthe.evilrobot wrote:

"John Robertson" <spam@flippers.com> wrote in message
news:J_OdnT_d4oCiSiTFnZ2dnUU7-fHNnZ2d@giganews.com...
On 2017/03/03 12:28 PM, pfjw@aol.com wrote:
Mpfffff..... Some clarification required.

FINE silver plating (most of it) *will not* tarnish from exposure to
air, nor will it form sulphur compounds - without other contributing
factors. Sterling silver (.925 silver) is an entirely different matter.

What is going on here electro-galvanic (galvanic action) *corrosion*
of the copper plating under the silver - and most things
electro-silver-plated other than brass are first copper-plated to
guarantee proper adhesion.

The black material noted is CuO, not tarnished silver.

Peter Wieck
Melrose Park, PA


Thanks, we've had many an Eprom with corroded legs that are from the
70s, in some cases the legs break off inside the IC sockets when the
EPROM is removed. Also this is common on some other ICs used in the
early 80s, such as Galaga which has Namco custom ICs, where again the
legs are corroding right off them.

Is there any way to arrest the process? Be nice to have something to
dip the legs into to cancel the corrosion, similar to using white
vinegar and water (50/50) to neutralize alkaline battery leakage
corrosion.

No idea whether its related - but when I serviced VGA monitors, I often
encountered brown glue that was probably applied to prevent components
from fatiguing their leads.

This stuff eventually became brittle and crumbly - and highly corrosive.
It frequently etched away component leads.

Once brittle it was fairly easy to chip away, but in the early stages it
was elastic like contact adhesive, and lighter brown like Evo-stik.

Very often a component like a resistor would come out encased in this
stuff and the leads completely eaten away.

I've quite often found problems with conformal coating, over decades, it
seems to trap moisture underneath as though hygroscopic/delequescent or
whatever its called

 

[N_Cook]

On 03/03/2017 21:08, Benderthe.evilrobot wrote:

"John Robertson" <spam@flippers.com> wrote in message
news:J_OdnT_d4oCiSiTFnZ2dnUU7-fHNnZ2d@giganews.com...
On 2017/03/03 12:28 PM, pfjw@aol.com wrote:
Mpfffff..... Some clarification required.

FINE silver plating (most of it) *will not* tarnish from exposure to
air, nor will it form sulphur compounds - without other contributing
factors. Sterling silver (.925 silver) is an entirely different matter.

What is going on here electro-galvanic (galvanic action) *corrosion*
of the copper plating under the silver - and most things
electro-silver-plated other than brass are first copper-plated to
guarantee proper adhesion.

The black material noted is CuO, not tarnished silver.

Peter Wieck
Melrose Park, PA


Thanks, we've had many an Eprom with corroded legs that are from the
70s, in some cases the legs break off inside the IC sockets when the
EPROM is removed. Also this is common on some other ICs used in the
early 80s, such as Galaga which has Namco custom ICs, where again the
legs are corroding right off them.

Is there any way to arrest the process? Be nice to have something to
dip the legs into to cancel the corrosion, similar to using white
vinegar and water (50/50) to neutralize alkaline battery leakage
corrosion.

No idea whether its related - but when I serviced VGA monitors, I often
encountered brown glue that was probably applied to prevent components
from fatiguing their leads.

This stuff eventually became brittle and crumbly - and highly corrosive.
It frequently etched away component leads.

Once brittle it was fairly easy to chip away, but in the early stages it
was elastic like contact adhesive, and lighter brown like Evo-stik.

Very often a component like a resistor would come out encased in this
stuff and the leads completely eaten away.

sorry wrong followup.
You failed to mention it going conductive

 

[N_Cook]

On 03/03/2017 21:05, pfjw@aol.com wrote:

On Friday, March 3, 2017 at 3:51:17 PM UTC-5, John Robertson wrote:

Thanks, we've had many an Eprom with corroded legs that are from the
70s, in some cases the legs break off inside the IC sockets when the
EPROM is removed. Also this is common on some other ICs used in the
early 80s, such as Galaga which has Namco custom ICs, where again the
legs are corroding right off them.

Is there any way to arrest the process? Be nice to have something to dip
the legs into to cancel the corrosion, similar to using white vinegar
and water (50/50) to neutralize alkaline battery leakage corrosion.

John :-#)#


The best way I have found - if at all possible - is a coat of flexible lacquer over the entirety. I admit to having a bottle of flexible fingernail polish hidden away amongst my other solvents for this sort of thing. Stop the air, stop the corrosion.

Peter Wieck
Melrose Park, PA

I've quite often found problems with conformal coating, over decades, it
seems to trap moisture underneath as though hygroscopic/delequescent or
whatever its called , an oily/ jelly type composition beneath, complete
with green copper carbonate corrossion product

 

[Phil Allison]

Sjouke Burry wrote:

Silver oxide conducts.

** You got proof of that ?

In any case, the black tarnish on silver exposed to air is Silver Sulphate - which is an insulator.


..... Phil

 

[Phil Allison]

Phil Allison wrote:

In any case, the black tarnish on silver exposed to air is Silver Sulphate - which is an insulator.

** That should be "Silver Sulphide" = Ag2S


..... Phil

 

[pfjw@aol.com]

On Saturday, March 4, 2017 at 12:25:50 AM UTC-5, Phil Allison wrote:

** That should be "Silver Sulphide" = Ag2S


.... Phil

True for sterling (.925) silver.
Fine silver - what is deposited by electroplating - does not form compounds with sulphur at anything near normal room temperatures.

Peter Wieck
Melrose Park, PA

 

[Phil Hobbs]

On 03/03/2017 05:11 PM, N_Cook wrote:

On 03/03/2017 21:05, pfjw@aol.com wrote:
On Friday, March 3, 2017 at 3:51:17 PM UTC-5, John Robertson wrote:

Thanks, we've had many an Eprom with corroded legs that are from the
70s, in some cases the legs break off inside the IC sockets when the
EPROM is removed. Also this is common on some other ICs used in the
early 80s, such as Galaga which has Namco custom ICs, where again the
legs are corroding right off them.

Is there any way to arrest the process? Be nice to have something to dip
the legs into to cancel the corrosion, similar to using white vinegar
and water (50/50) to neutralize alkaline battery leakage corrosion.

John :-#)#


The best way I have found - if at all possible - is a coat of flexible
lacquer over the entirety. I admit to having a bottle of flexible
fingernail polish hidden away amongst my other solvents for this sort
of thing. Stop the air, stop the corrosion.

Peter Wieck
Melrose Park, PA


I've quite often found problems with conformal coating, over decades, it
seems to trap moisture underneath as though hygroscopic/delequescent or
whatever its called , an oily/ jelly type composition beneath, complete
with green copper carbonate corrossion product

Parylene is about the most impervious common coating, but any plastic
has orders of magnitude higher gas diffusion rates than any metal. In a
humid environment, water will penetrate until the net flux is zero, so
if you have nasty hygroscopic corrosive crud underneath, your board is
still doomed.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net