[sdiy] black flaky chip legs: what does this indicate?

[Roman Sowa]

I have observed this in new parts also. Maybe not totally black, but 
first turning yellow, then darker, to metallic dark grey/graphite. It 
happens to many parts with most popular modern plating - E4/G4, which is 
Ni-Pd-Au or other similar variants. It kinda solders, but not as good as 
older G3 plating which is pure Tin. And G3 leads are clean as new all 
the time, and solder really well.

Roman

W dniu 2020-11-02 o 18:34, Steve Lenham pisze:
> I work extensively on Lexicon effects from the late '70s/early '80s 
> (which are built form a LOT of 74-series logic) and see this all the 
> time.
>
> As others have observed, it is associated with TI parts from a 
> particular era, though I have actually observed the same thing on some 
> Z80 CPUs of similar vintage. It seems to happen purely from exposure 
> to the atmosphere and does not require battery leakage or anything so 
> dramatic (though Lord knows early Lexicons suffer from that too). ICs 
> from other manufacturers of the same age and in the same board will be 
> completely unaffected.
>
> I'd be very interested to know exactly what the TI ICs are made out 
> of/the chemistry of why this happens, not least because I dream of a 
> quick chemical cleaning process for those that are not too far gone.
>
> At a guess, the blackening looks rather like what you get on silver. 
> It is easy to remove with a fibreglass pencil and this temporarily 
> leaves a very shiny finish. However, on closer inspection the surface 
> plating often seems to be pockmarked with corrosion and/or peeling off 
> the pin. Unfortunately, once exposed, the underlying substrate seems 
> to suffer from rust-like corrosion which weakens the pin. Eventually 
> they snap off at their thinnest part.
>
> Cheers,
>
> Steve L.
> Benden Sound Technology
>
>
>
> On 02/11/2020 03:37, Doug Terrebonne via Synth-diy wrote:
>> Yep see those blackened socketed TIs all the time especially in 
>> OB-X/Xas.
>>
>> Doug
>> synthparts.com
>>
>> On Sunday, November 1, 2020, 3:03:36 PM PST, KA4HJH 
>> <ka4hjh at gmail.com> wrote:
>>
>>
>>
>>> On Nov 1, 2020, at 5:26 PM, Kenny Balys <kenny at beatkamp.com 
>>> <mailto:kenny at beatkamp.com>> wrote:
>>>
>>> Yes!!!!!
>>>
>>> They were both TI and the device was manufactured in 1979.
>>>
>>> Both IC's were socketed. I had to pull disconnected legs out of the
>>> sockets after removing the chips. They shed their legs.
>>
>> I saw this happen once with a Bally pinball machine from the late 
>> '70s, the first generation electronic ones. The logic board was 
>> damaged by a leaking NiCd battery (the most common mode of failure) 
>> and when I tried to pull the ROMs out of the sockets the legs just 
>> snapped off. I don't recall the manufacturer.
>>
>> I don't know if the battery had anything to do with it. It's mounted 
>> at the bottom of the board and the firmware is up at the top. I've 
>> seen these boards with much worse corrosion and the ROMs/EPROMs were OK.
>>
>>
>> Terry Bowman, KA4HJH
>> "The Mac Doctor"
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