6 Sep
2014
6 Sep
'14
2:24 p.m.
Hi Brett,
Ah, very interesting; I did not know that. Yes, these are all TI ICs in
plastic DIP package produced in any of three facilities that I mention in
my prior message. I haven't inspected the "corrosion" that closely or
actively tried to "remove" it yet so now I'm not 100% clear if what I am
seeing is oxide residue from the plating, or if it is actual corrosion... I
just eyeballed it and assumed it was rust; the "residue" on the pins is a
dark red-brown sort of color; maybe a little darker than I'd expect iron
oxide to look, actually, but my examination wasn't under the best light.
I haven't gotten to the point of testing anything under power but the ICs
seem to be fairly securely attached to the board; I don't see any broken
pins and I can't easily wiggle anything around. Obviously these will need a
lot of cleanup but nothing unsalvageable. Even if I do have to replace the
odd part here and there, most of the affected components should be easy to
source; nothing too obscure.
Thanks for the response! It certainly explains why the phenomenon was
limited to TI ICs!
Best,
Sean
On Sat, Sep 6, 2014 at 3:14 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
> On
06/09/2014, Mattis Lind <mattislind at gmail.com> wrote:
>> What is the experience when it comes to different manufacturer and
> plastic
>> DIP TTL? Which are better, which are worse after 40 years?
On 2014-Sep-06, at 8:31 AM, Sean Caron wrote:
Can I hijack this thread for another IC quality
related question?
I'm in the early stages of trying to restore a ROLM CBX 8000 and I'm
finding that on certain cards; mostly 8550 shelf expanders and 8551
16-channel coders; there are noticeable amounts of TI 7400 series logic
produced in the following facilities:
EL SALVADOR
MALAYSIA
TAIWAN
where the IC leads have experienced, in my opinion, "excessive
corrosion".
Date of manufacture on these parts ranges from
mid-1970s to early 1980s.
ICs in the switch produced by other vendors e.g. AMD, Mostek, Zilog,
Intel,
Rockwell, GI, Signetics, Motorola, OKI, etc as
well as passive components
don't seem to really have this problem; leads are free of corrosion; it's
really just 7400 series "little logic" from TI on these two card types,
where the corrosion is occurring.
Has anyone ever seen this sort of thing before? Before I got the unit,
AFAIK, it was stored in a nominally dry-and-out-of-the-elements but not
really climate-controlled storage locker for probably at least a decade
or
so. I've had other bits of equipment spend
some time (years) in lockers
and
never seen any internal corrosion... the
corrosion on 8550 and 8551 cards
occurs across all six shelves of the PBX from top to bottom so it doesn't
appear that, say, one part of the PBX was any more exposed to the
elements,
corrosive atmosphere, etc.
No meaningful corrosion on the PBX frame, card shelves, terminal strips,
connectors, fuse panel, ... any other metal component, really.
Was TI cheaping out on the metal used for package leads for a little
while
there, or ??
To my observation, the answer there is yes and no.
Some plastic TI TTL ICs from a period somewhere around the mid/late-70s
were manufactured with steel pins that corrode underneath the plating. They
might look fine but simply fall off with the slightest stress, or develop
intermittent conductivity.
But with that said, a lot of TI ICs from around then show discolouring on
the pins that looks horrible and suspect, but the discolouring doesn't
necessarily imply the corrosion underneath. I believe the visible
discolouring was (often) just oxide of the silver final plating of the
pins. It shows up on TI because they were the only ones doing that plating.
I think the TI steel-pin rot is the only wide-spread IC fault I've really
correlated to a particular manufacturer/period, and I don't know whether it
was company-wide or production that came out of maybe just one of their
plants. (It can occur with other manufacturer's steel pins but then it
seems to be more a result of particularly bad environmental/storage
conditions of the machine and not really a surprise.)
When it comes to plastic, well, there were reasons ceramic was an option.