[time-nuts] New frequency standard, Mercury better than Cesium?

[Brooke Clarke]

Hi Chuck:

I think it will take 4 to 6 years for the tin whiskers to grow to the 
point of shorting out IC packages, relays, etc.  That's why NASA has 
reactivated the work they have done on whisker growth.  See:  
http://nepp.nasa.gov/whisker/
It seems that they do not have a good theoretical handle on what causes 
whisker growth  (or what stops it) and so the "qualification" tests that 
manufacturers are trying to use will most likely not work.  NASA says 
the only way to know is to see if you can grow whiskers on every lot of 
tin plated parts, or better use lead to kill the whisker growth.

Have Fun,

Brooke Clarke

-- 
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Chuck Harris wrote:

>Hi Said,
>
>I'm inclined to believe that a fairly short period of time after
>the world goes lead free with electronics, there are going to be
>disastrous numbers of failures.  Basically, the electronics industry
>is being asked to forget all of the advances it has made in manufacturing,
>and production, and reinvent the wheel, in a big way.  I can only hope
>that sanity will return, and RoHS will be modified to something more realistic.
>
>Just consider the amount of lead in a car battery, and consider how
>one improperly discarded car battery will introduce more lead into the
>environment than several metric tons of improperly discarded electronic
>equipment.
>
>As to China, they are already ready to make things any way you want
>to pay them to.
>
>-Chuck
>
>SAIDJACK at aol.com wrote:
>  
>
>>Hi Chuck,
>> 
>>yes, all test equipment is excempt from RoHS, until between 2009 -  2011. 
>>Europe is not sure how long they will keep this exemption in  effect.
>> 
>>There are so many legacy products that are vital to the industry and that  
>>will not be re-designed that I think the exemptions will continue beyond  that.
>> 
>>Doing Lead-free has many reliability issues, let me just mention shorts  
>>caused by tin-whiskers, and the problems of visually identifying a cold-solder  
>>joint... The assembly houses I have talked to hate doing lead free work for  
>>critical, expensive items.
>> 
>>How much test equipment ends in a land fill? Probably not too much due to  
>>all of the gold used in it, the collectors' value etc.
>> 
>>Also, who is going to test all the products for compliance? It's probably  
>>very easy to get away with not complying. I would guess this will happen to a  
>>lot of products made in China...
>> 
>>bye,
>>Said
>> 
>> 
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