Joe,

I think it is impossible to give a blanket statement about lead free
component compatibility with lead based solder.  You do not give a use  condition or
expected life for your assemblies, but based on your address, I you  are
possibly in the military.

Your question is similar to the re-work problem now facing many RoHS exempt
industries, including the military - what to do with lead free parts now
coming  in to repair legacy electronics.

Several of us, including Carol Handwerker now at Purdue University, are
involved in a study to help the military decide on re-work procedures. A
tremendous amount of study of the problems has already gone on by great  organizations
such as JCAA-JGPP aging aircraft, CALCE, and iNEMI.

A short summary of compatibility seems to be - what stress will the solder
joint be under in the expected useful life of the assembly?  Of course,  this
varies with the component, joint size, compliant lead, etc.

Low stress joints - through hole with lots of volume, compliant lead
devices, etc seem to have wide latitude to mix component and board finishes with
different pastes including lead free.

High stress joints - BGAs especially high ball count, ceramic components
with different TCEs from the board, and (heaven forbid) flip chips with almost
no solder volume, are quite sensitive to mixed constructions.

All of this activity seems to be gelling into consensus recommendations,
just as all of us settle into living in the electronics manufacturing world with
RoHS regulations.

Denny Fritz
SAIC, Inc.


*************************
In a message dated 8/9/2006 10:04:52 A.M. Eastern Daylight Time,
[log in to unmask] writes:

As  everyone knows, many smt components now have Pb-free finishes such  as
NiPdAu by TI that can still be soldered using leaded solder. Would  someone
please let me know where I can find a cross reference matrix, etc.  showing
the various backward compatible Pb-free finishes that work with  leaded
solder and any issues!




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