Frank,

There were two papers given on this topic at the JEDEC Third Annual
International Conference on Lead Free Electronic Components and Assemblies
in San Jose this April:

Reliability of Mixed Pb-free and Pb-alloys in a Rework Scenario

Miloš Dušek, Alan Brewin and Dr Christopher Hunt
Materials Centre, National Physical Laboratory
Teddington, Middlesex, TW11 OLW, UK

The Effects of Trace Amounts of Lead on the Reliability of Six Lead-Free
Solders

Thomas A. Woodrow, Ph.D.
The Boeing Company
Seattle, WA

I am not sure if these papers are freely availabe on the JEDEC web site.

Best regards,
Corfin Industries LLC


Joe Zaccari
Military Programs and Sales Manager

603-893-9900 Office
603-893-6800 Fax
603-498-7854 Mobile


-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Frank
Hacken
Sent: Friday, June 20, 2003 5:33 AM
To: [log in to unmask]
Subject: [LF] backwards compatibility of SnBi


Dear all,


I've been to the lead-free conference in Brussels. There I heard several
contradictions on the application of Bi in lead-free soldering. In an
effort to try to find the real answer I would appreciate any information
about this matter:
In the coming years we will be faced with SnBi finishing and still solder
with SnPb solder during the transition to lead-free. (Maybe we are already
applying this alloy without knowing)

As I understood up till now:

Sn-Cu-Bi Solder
The overall understanding is, that there is no problem in backwards
compatibility with using Sn-Cu-Bi solder. So if the component finish is
SnPb and the solder is Sn-Cu-Bi there is no problem with ternary phases
Sn-Pb-Bi that has a very low melting point (98°C). This would be the case
if there is minimal 20%wt Bi in the solder.
The only concern with Bi in solder is fillet-lifting in wave-soldering. It
is not decided yet if this is acceptable. Joint strength would not be a
problem is the overall feeling ?


Sn-Bi component finishing
Till now I understood that Sn-Bi finishes are not backwards compatible with
SnPb solder. It was said that this could more easily give ternary phases
SnPbBi in especially reflow soldering.
Also is said that it is no problem because the ternary phases are very
small. And it would not be a problem if there is SnBi(5%) on the
components.

My question is :  Is there any investigation done in backwards
compatibility for SnBi component finishing ?
            If so, what percentage Bi in component finishing is the limit ?
            Can anyone confirm that there is no problem with SnBi finished
components with SnPb solder ?

I appreciate any information about this matter !

Kind regards,

Frank.

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