Dear Christopher,

This project by Lucent Technologies raises a few questions that I would like
discussed on the leadfree forum:

Pure Tin
It is claimed in a news release from Lucent Technologies on April 28, 1999
that Murray Hill has developed a new electroplating process for pure tin
that inhibits whisker growth. From the technical work I have read about
whiskers the cause is attributed to internal stress in the tin deposit. This
is normally overcome by reflowing the deposit, however, in the case of
forming components after plating the resultant internal stress can lead to
whisker formation.
I have also read an alarming report from the Department of Health, Education
and Welfare issued on March 14, 1986 dealing with failure of pacemakers due
to tin whiskers.
Has the risk of whiskering of pure tin been overcome?
I assume from Lucent's new project that pure tin is not acceptable.


Viable alternatives to tin-lead electroplating solutions.
Lucent talk about developing viable processes for electroplating tin-silver
and tin-bismuth solder as a drop-in replacement for tin-lead solder.
As far as I am aware tin-silver will most likely involve cyanide chemistry
which is hardly environmentally friendly. The alloy fails the EPA test
designed to simulate waste disposal and groundwater contact. The price of
silver is significantly higher than lead.
Tin-bismuth, there are two concerns over the use of tin-bismuth, the first
is the availability of bismuth, the second is the reaction of lead with
bismuth which forms a brittle intermetallic. It is going to be very
difficult to ensure that all components are leadfree.
The only obvious alternative is tin-copper, which although it has a high
melting point it is lower than pure tin. The advantages are that the
chemistry should still be based on methane sulphonic acid and therefore
there should be little plant modification required. The cost are reasonably
comparable to tin-lead solder. The down side is that this is most alloy
composition vary with the applied current density, it therefore may be
impossible to control the process.

My final comment is that the European Commissions draft proposal allows for
the use of lead as an alloying element in steel, aluminium and copper. In
the case of copper there can be 4% lead by weight, why is this not also
applied to solder?
The electroplating of a 95/5 Sn/Pb solder would be by far the simplest route
to lead reduction. The original reason for leadfree solder was to eliminate
lead from tin cans, this was suggested by the Organisation for Economic
Co-operation and Development back in 1990, they did not consider solder used
in electronics a risk as the quantity of lead used was not significant.

I look forward to receiving comments on the above points.

Best regards,

David Gowlett
Technical Director
Palmer Plating Ltd



-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Christopher
Jorgensen
Sent: 14 October 1999 18:10
To: [log in to unmask]
Subject: [LF] ATP Lead-Free Solder Project


Lucent's Electroplating and Chemicals Services (EC&S) is sponsoring a
project to
develop commercially viable electrochemical processes to enable the use of
tin-silver
and tin-bismuth as drop-in replacements for lead-based solders. The project
is being
done with the support of the Advanced Technology Program (ATP) of the
National
Institute for Standards and Technology (NIST).


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