Jack and all:

There are no purely technical issues.  Good engineering is supposed to
consider cost alternatives and other tradeoffs.

For example, where would you classify the letter by the gentleman from
Daimler Chrysler who reported that SnAgCu alloy is unreliable at high
temperatures and high duty cycles under-hood.  He said they won't depart from
SnPb unless forced.  Shouldn't everyone be able to read that?

Or take Alan Rae's (Cookson) many valuable comments on the economic as well
as performance considerations of lead vs. lead-free.  Would these be banished
to some ghetto where the technicians won't see them?

Or take the comments by the gentleman from TI.  He has read the Jan 2001 NEMI
report that describes IC package moisture sensitivity degradation due to
assembly reflow ramp to 260 degrees C.  He sees great hope for lead-free by
implementation of two measures.
(1) Reducing peak temp to 235 degrees C and (2) Development of new material
sets that won't degrade at high peak temps.

Well, don't we have a right to ask some technical-economic questions?  How
much does the belt have to be slowed to allow for an even gradient across the
assembly?  How much will this affect manufacturing throughput?  Would new
reflow equipment be required? How would the process window be affected? What
additional thermal stresses will the longer dwell time at 235 degrees C place
on silicon, package, other components?  I really would like answers to these
technical-economic questions.

As for development of new "material sets",  it is true that vendors will be
motivated by the chance of business.  But they will be constrained by market
size in an environment of great uncertainty.  So I challenge his "optimism"
on both technical and economic grounds.  They cannot be separated.

Harvey Miller

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