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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