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

[Roman Sowa]

Mybe there's a rule, but sometimes parts have different suffix for 
different plating, this is then clearly indicated in datasheet, 
sometimes G3/G4 are explicitly given in part number so it's easy to 
tell, and sometime's it's a lucky guess and you find out only when parts 
arrive.

Roman

W dniu 2020-11-04 o 23:13, MTG pisze:
> Are there part numbers (suffix?) for the items for sale that indicate 
> this difference. As mentioned, I've bought recent TTL from Mouser (I 
> suspect) that has the shabby finish. I try to avoid buying from Jameco, 
> but did also buy from CircuitSpecialists.
> 
> GB
> 
> On 11/2/2020 12:21 PM, Roman Sowa wrote:
>> 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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