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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