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April 1997

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From:
"ddhillma" <[log in to unmask]>
Date:
Thu, 03 Apr 97 17:33:43 cst
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     Hi Jerry -
     
     With the decline of ceramic components and the increase of plastic 
     components with this be an issue again or because of past lessons 
     learned be a non-issue?
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Re: Low-alpha Lead
Author:  [log in to unmask] at ccmgw1
Date:    4/3/97 4:25 PM


Roy Alain said:
     
>I've heard about a need in the packaging industry for lead with low content 
>of alpha-particle emitters.  Apparently, alpha particles may causes soft 
>errors if the lead solder is located "near" the component.  From what I 
>understood, old lead may be used for that application, but there would be a 
>need to secure the long term supply through purification of contemporary 
>source of lead. I had a quick look in the litterature but found very little 
>on this subject.  Can you help me on the followings:
>
>Is there a real need for "low-alpha lead" in the current industry or is it 
>more a research subject ?
     
Probably not a large demand, IMO.
     
>What are the specifications for this products ?  I saw anything from less 
>then 1 to less then 0.001  count/cm2/hre.
     
Don't know. Check issues of _The IBM Journal for R&D_ back to circa 1980.
     
>Have you heard about process other then Laser Separation (see ref. on AVLIS 
>below) that can be used for lead isotope separation ?
     
Heck, no; I flat out missed even the old Laser Separation!
     
>Any information regarding this product would be very welcome  (market, big 
>players, supply, applications, ...).
     
OK, I was once a process engineer for Mostek, trying to solder RAM dice to 
leadframes, so we looked into this long ago...
     
Alpha emitters in lead are present since lead is a decay product of natural 
radioactive elements (I'm sure you knew that).
     
The "soft errors" which you refer to are (were?) a problem with RAM memory 
in the early 1980's. At that time, many RAM's were packaged in ceramic 
DIP's, and the emission from the ceramic material could be shown to cause 
bits to flip on the NMOS structures of RAM dice. IBM and others could 
demonstrate this phenomenon. The most common problems occured with ceramic 
vs. plastic packages.
     
My opinion is that this did indeed occur at some level near the vanishing 
point, but that the entire industry overreacted, such as the IBM PC using 
"by 9" redundancy in their PC memory architecture for many years. This was 
to permit error correction of "soft errors", theroetically. It really did 
not work too well, but that's another story. Some of these resarchers went 
on to write scripts for the X-Files, I think.  ;-)
     
Alpha particles can be stopped by a monolayer of most any solid material 
and thus even when the device is exposed to higher levels of radiation, a 
thin pure die coat inside the device package is protective. Even transfer 
mold compounds of the 80's were subjected to strict refinements to avoid 
the dreaded alpha emission problem.
     
There are natural sources of low alpha lead ore (think the deposits in 
Missouri are some of the best in the world in this regard), and from 
recollection; the best source is from recycled European lead roofing 
material.
     
I have no doubt that there is still some market for low alpha lead. Most of 
the final users would be in the memory or hybrid package business, and I 
would think the solder companies like Cookson or Multicore have some 
interest as suppliers to these users.
     
Perhaps that highly technical wordsmith, Dr. K. Tellefsen would have some 
suggestions for you. That's who I'd ask.
     
     
regards,
     
     
Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com
     
     
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