it was long long time ago (early 90s), some of us (eng. and r&d chaps) were
interested in the same topic.  After realize the limitation in the world
supply of elements, lead free was considered as a difficult goal to acheive
for the near future (approx. 10 years at the time of chat).
  All the elements can be used to replace lead, with the production quantity
and avaliability in the world, are limited.  In, Sb, As, Au are not very
common elements on the earth.... Ag is the one can be widely used as Pb (but
the mechanical properties!).  The price of many elements at current stage
are not that expansive, however, the price is likely to go sky rocket when
the demand heats up. particularly, with those elements only has limited
avaliability on the earth (someone managed to get a world metal production
overview or resource map to get the point cross very effectively, at least
convince me).  At the time, some of us agreed that the best way is to reduce
Pb usage (we some what gave up the Pb free idea, after the discussion got
into the power circuit requirement and reducing feature size, etc.  Pb is
very ductile material.  It is a concern about mechanical properties of fine
pitch joint characteristics, electrical and mechanical, over the temp
range)...Here are few of the 2 cents flying around at the time (non-official):
(1) integrate as many device as possible to the chip level = reduce I/O,
reduce lead usage.  MCM or others method may be useful.
(2) recycle the lead.  Limited Pb usage for 2nd level package (mostly Pb
usage are on the 2nd level package - module to PWB).  problem is that
recycle Pb will be more expansive than the fresh supply of Pb... no
resolution there...
(3) epoxy or other methods (sockets, wire bond, etc.)were discussed.
However, it was believed that conductive epoxy and others may be useful to
commercial (office environment) products, it may be difficult for extream
environment.  (At the time, Z-axis conductive adhesive is limited for LCD
only.  some of the conductive adhesives are still in the early develop
stage.  Surface finishing of the device is the other issue.... You need a
bondable surface....Normally, the device surface finishing are either
solderable, or bondable, but not both...)..Supply of the bondable surface
device is very limited at the time.

Things changed a lot since the discussion we had long long time ago... With
many conductive adhesives and alloys on the market now, it may be look
rather different (promising) than a group of us sat down had few drinks.
Sorry to say that, at the time of discussion, Pb free things were not look
very promising even after few drinks.  Hopefully, the UK chaps will give us
some good news, such as some ground breaking technology advances. (every 3
to 5 years is so called a "generation"... I feel very old).

jk

At 11:11 AM 3/19/99 EST, you wrote:
>In a message dated 3/19/99 6:08:10 AM Pacific Standard Time, [log in to unmask]
>writes:
>
><< Something which has been conspicuous by its absence on the IPCs web site.
>
>Neil Atkinson
>Quality Manager
>Stadium Group plc
>England
>
>I said it once before and I'll say it again, I feel that somebody stands to
>make a lot of money from all of us eliminating our usage of lead, what else
>can it be?
>
>This is just my opinion...
>
> -Steve Gregory- >>
>
>...and just as conpicuous is the lack of argument to my opinion...really makes
>you wonder doesn't it?
>
>-Steve Gregory-
>
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