King-Ning Tu talks with
ScienceWatch.com and answers a few questions about
this month's Fast Moving Front in the field of Materials
Article: Six cases of reliability study of Pb-free
solder joints in electronic packaging
Journal: MAT SCI ENG R, 38 (2): 55-105 JUN 14 2002
Addresses: Univ Calif Los Angeles, Dept Mat Sci & Engn,
Los Angeles, CA 90095 USA.
Univ Calif Los Angeles, Dept Mat Sci & Engn, Los
Angeles, CA 90095 USA.
Why do you think your paper is highly
The report is about failures in Pb-free solder joints used in electronic
consumer products. Because there is a ban on using Pb-based solders by the
Congress of the EU, the electronics industry has had to apply Pb-free
solders to their products without undertaking enough study about
reliability. A high rate of failure is found, for example, due to
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Due to the trend in miniaturization and the increase in functionality, the
reliability of solder joint in microelectronic devices is of concern, even
for wireless and handheld consumer electronic products. A new discovery is
that the current crowding in flip-chip solder joints has induced a fast and
new mode of failure that was not known before. The methodology used to
study electromigration in flip-chip technology is presented, with knowledge
and analysis provided.
Would you summarize the significance of your paper in
While Pb-free solder has been used in plumbing, until recently, it had not
been found in electronic consumer products. Our paper reports on what are
the yield and reliability problems when Pb-free solder is being used in
electronic consumer products.
How did you become involved in this research and were
there any particular problems encountered along the way?
I have worked on solder materials for over 40 years, finishing my Ph.D.
thesis on Pb-Sn alloys in 1968. Since then, I have remained keenly
interested in solder alloys and their applications.
Where do you see your research leading in the
The trend in the electronics industry is toward the use of smaller and
smaller solder joints. The reliability problems will become more serious
and they will not easily go away. I shall try to bring more scientific
understanding to the problem in electronic packaging technology.
Do you foresee any social or political implications for your
Since Pb-based solder is toxic to health, our research on Pb-free solder
will benefit society.
King-Ning Tu, Ph.D.
Department of Materials Science and Engineering
University of California, Los Angeles
Los Angeles, CA, USA
Keywords: Pb-free solder joints, Pb-free solder, flip-chip
solder joints, electromigration, flip-chip technology flip-chip solder
joints, Pb-Sn alloys