6 Sep
2014
6 Sep
'14
12:14 p.m.
> 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.