Chip failure and air corrossion products

That was pretty much implied by it becomes corrosive.

It would be sulphate if exposed to sulphuric acid.

The sulphide is mainly produced by a component of car exhaust - or your farts if you've been eating eggs.

Catalytic converters stop your silverware going black (or make it go black even quicker - I can't remember which) - and kill thousands of asthma sufferers.

** As you seem to be the only person in the world who thinks that - you need to post a link to back it up.

Do you know what "black leg" corrosion is ?

Commonly seen on the leads of small signal transistors made in Japan in the 70s. It often results in the device going noisy or failing completely. Marantz stereo amps were notorious for it.

.... Phil

Hey Phil,

Can you provide a link to more in depth discussion on your black leg corrosion? I did a quick search and could only find one reference, and it merely said watch out for 'black leg corrosion'?

I have run into a lot of Namco branded ICs from Japan, made in the late

70s that have this problem...

Thanks!

John :-#)#

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** Not much to be found on the net, but something most service techs have seen.

Bit like the "yellow glue" problem that has plagued countless items and still is.

** It's got be due to silver plating the leads.

.... Phil

I'm sure they thought that silver plating was a good idea, instead of planned obsolescence.

Thanks,

John :-#)#

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(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."

in the 70s. It often results in the device going noisy or failing completel y. Marantz stereo amps were notorious for it.

seen.

still is.

No, Phil, it is not *DUE* to the silver plating on the leads, nor is the si lver plating on the leads even contributory to the primary failure, though it does contribute to the visual results.

Let me start over as you clearly need the little-steps-for-little-feet appr oach.

a) Silver electroplating does not adhere well to anything but copper, low-t in bronze and very low zinc brass. b) So, most materials to be silver-plated are first flash-plated with pure copper. Otherwise the failure of the silver-plate due to simple peeling wou ld be quick and fast. c) Over time, the different coefficients of expansion, simple age, heat/coo l cycles and other environmental factors cause the copper plating to crack, microscopically, initially. d) At which point, electrolysis takes place between the copper and base-met al of the lead/pin/whatever. e) The first product of failure is CuO - because typically the substrate (b ase metal) would be sacrificial to the copper, in this case, the copper bec omes sacrificial to the silver. f) CuO is a black semi-conductor, still (very rarely) used in very heavy du ty rectifiers. g) Silver reactions with sulphur do not produce a grainy material, Even ext ensive reactions. h) Copper oxides, with the fine silver still attached, are grainy. The fine silver will be entirely covered by the copper oxide, but will not actually react itself.

So, that you state something *MUST* be due to something else does not make it so. Jewelers and metalsmiths have been exploiting this phenomenon for ma ny years and it is very well understood. You need to learn that there is an entire world outside your cave.

Peter Wieck Melrose Park, PA

** Shame you have NO links whatever to back up this arrant nonsense.

** Go f*ck yourself - asshole.

Wieck is a psychotic, raving lunatic.

I snipped his manic ravings.

To spare gentle the readers here.

.... Phil

file:///C:/Users/Peter/Downloads/corrosion_of_silver_plated_copper_conductor.pdf

Phil:

It's a big world out there - first link I found, and pretty much describes the situation nicely.

But, I am sure you will spin it in your own inimitable manner.

Peter Wieck Melrose Park, PA

Come on, Peter. Another link to your C: drive?

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Never piss off an Engineer! 

They don't get mad. 

They don't get even. 

They go for over unity! ;-)

See if this works - or use the title:

Corrosion of Silver Plate Copper Conductor

If one hits the link, it automatically downloads the .pdf, making a C: Drive link - which I did not notice.

Peter Wieck Melrose Park, PA

My first job was fault finding huge desk calculators that only did the most basic functions and contained about 200 DTL chips.

Most of the chips had silver plated pins and I never had a fault because of that - a few chips had gold plated pins, there may have been less than half-dozen faults because the alloy interface became an insulator (there was no inherently dodgy RoHS soldering back then).

You could always tell the silver plated ones because the pins were black. The tinned ones never got past dull grey.

Couldn't open that - maybe someone formatted it.......................

Any connection with metalisation creep ? I associate with silver plating of the segments of ceramic resonators, the thin segment gets metal migrating over the edge and going ohmic and failure of RF/IF stages.

Absolutely a connection. Silver-Mica disease in vintage radios is one obvious manifestation of such creep.

A very simple explanation here:

As silver is an excellent conductor, it takes very little for a current path to develop.

Although this is not absolutely specific to your question - the phenomenon and mechanisms are the same.

It is interesting to note that what is common to all these various discussions around silver and how it affects most electronics does not involve Sulphur, or actual corrosion of the silver itself.

Peter Wieck Melrose Park, PA