[time-nuts] 5070B once more.... (actually 5370A fans)

[David Forbes]

Hal Murray wrote:
>> The reason for the fans is to prevent premature failures of the
>> silicon devices due to thermal degradation. The life of a silicon
>> chip is halved for every 10C temperature increase, more or less. 
> 
> I was going to make a similar comment, but got sidetracked poking around 
> google.  I didn't find a good/clean article.  Does anybody have a good URL?
> 
> Doubling every 10C is the normal recipe for chemical reactions.  I think that 
> translated to IC failure rate back in the old days.  Is that still correct?  
> Has modern quality control tracked down and eliminated most of the 
> temperature dependent failure mechanisms?

Hal,

The old standby is MIL-HDBK-217F:

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=53939

It is quaint, but they based it on years of experience. They did a lot of 
testing of the chips and created mathematical models that worked as well as any 
model can, given the clumpiness of failures.

P.5-13 gives the temperature failure rate multiplier for ECL chips:

25C  0.10
45C  0.27
55C  0.42
65C  0.63
75C  0.94
85C  1.4
95C  1.9

So my off-the-cuff guess of failures doubling for every 10C rise is not too wrong.

--David Forbes, Tucson