[sdiy] advice please -- aging chips and caps

[ASSI]

On Saturday 09 August 2003 20:33, Scott Gravenhorst wrote:
> Are recently manufactured ICs still subject to this?  If the old
> ones only last 15 years (expected life), then what of new ones?

Each and every one is designed for a certain operating lifetime under 
certain operating conditions. That doesn't necessarily mean they will 
fail after that time, just that they are not tested for a longer 
lifetime. Most of the parts should have a far longer than the 
data-sheet lifetime, both because the failure statistics mandate it and 
because there is some margin in the qualification tests. Exceeding the 
maximum operating conditions however shortens the lifetime drastically, 
even if it happens just once and for only a short time. About the only 
things that can damage an IC while it is not being used is ESD and 
(large) temperature cycles.

The ESD robustness of original 4000 series IC is not really good, so 
you should really always follow the proper handling procedures. I don't 
know if the later improved series have gotten an ESD overhaul, but good 
ESD structures take up a lot of area and IMHO that doesn't go together 
with parts that often cost only a few cents more than their package. 
Most people assume that the IC dies instantly from an ESD pulse, but 
that is typically not the case (especially if someone is trying to 
prevent ESD by insufficient means) - degraded performance and 
subsequent early fail is much more likely. Also a pre-damaged IC will 
likely not live through another ESD event, the protection structures 
are normally not designed to withstand repetitive ESD.

Metal migration actually comes in two flavors: stress migration and 
electromigration, the latter is significantly different for DC and AC 
currents. They are both kept in check from the manufacturing side by 
optimized processing, additional layers and anneals. Some of these 
things have only recently been developed and/or understood sufficiently 
well to take full advantage of them. For the design side there exists a 
slew of electromigration design rules. As with all design rules you 
have to make some assumptions and for instance a 4069 being used as an 
op-amp probably wasn't on the mind of the designer.

>  I'd prefer that they outlast *me*.  This is pertinent for me
> because I have a 4000 series fetish.

Hmm, what kind of longevity do you expect for you and what's the duty 
cycle on your 4000 series IC?


Achim.

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