21 Apr
2012
21 Apr
'12
6:34 p.m.
On Apr 21, 2012, at 1:35 PM, Tony Duell wrote:
I hate to tell you this, but my comments are based on actual, practical,
observations. Not 'what the theory says'.
OK. How many 1,000,000's of parts have you looked at? What long term statistical
analysis have you done?
Extrapolating long tail effects from single samples does not yield accurate results.
Not based on the ICs I have to replace I'm not?
Small sample size.
Hmm... I am tlaking abvout the reliabiltiy of the whole system. In other
words, how often do I ahve to fix it? What has failed? It may be that the
IC has failed because it was essentially misused (supply glitches,
whatever), but a device more susceptable to those is likely to lead to
prodcut that fails more often.
All things being equal complexity will *tend* to result in a less reliable system.
However, holding all things constant is usually not possible. So making general
statements, is a bit of an overgeneralization.
I would argue that todays computer systems are *much* more reliable than
the systems that were in general use 10-20 (or more) years ago.
TTFN - Guy
My expeirence is that more compelx ICs are
noticably less reliable than
simple ones.
That's much too simple analysis even if it were correct. Failure rates in
ICs are primarily down to processing, packaging and handling (and to a
lesser extent die area), not complexity.
In other words, I'ev; had many thousands of things across the bench by
now. And I can assure you that complex ICs, modern ones, old ones,
whatever, are mcuh more likely to be dead than simpler ones.
Still a small sample set.
I would think the 555 had a much better lifetime than any
microcontrolelr
therefore.
You would be wrong however. Today's ICs have a much better lifetime.
Statistically today's commercial grade ICs have a significantly better
lifetime than military grade ICs of the 555 era.
The origianl 555 (as opposed to the 7555, etc) is large-ish junciton
bipolar and thus less likely to suffer static damage than a MOS
microcotnroller. It also has a much wider supply votaeg range and is
less
likely to be damaged by supply problems.
That's not a definition of reliability - it's one of robustness. Within
their specifications the 555 would be less reliable (IMHO of course).