Mechanical behavior of lead-free solder materials for advanced
automotive microelectronic packaging
P. Vinci and Michael R. Notis
Environmental concerns have led to a move toward lead-free solders for
electronic packaging. At the same time, as package and board packing
density increase to accommodate ever-decreasing size requirements,
increased power density and use conditions (such as in automotive
under-the-hood applications) call for substrate materials and assembly
designs that provide for better thermal management. Both of these
issues impose serious design and manufacturing issues upon the
production of advanced electronic devices and assemblies. The choice of
substrates, metallurgical coatings and solders has major effects on
thermal matching and resulting creep-fatigue behavior, stability of
microstructures, and the formation of reaction products at
metallurgical interfaces. The purpose of this investigation is
therefore to examine the compatibility of new lead-free solders, such
as Sn-Ag-Cu and SN-Ag-Bi based alloys, with new package and board
materials; and consequently, to investigate assembly requirements and
Shown on the left is an SEM micrograph of nanoindentations
in a lead-free solder alloy. The micron marker in the upper left is 10
micrometers long. The indents were made at room temperature.
The same indents as imaged directly by the Hysitron
Triboscope indenter tip. Material pileup can be clearly seen
surrounding each indent.
- investigate nature and kinetics of reactions between selected
solders and chip/substrate metallurgies
- characterize mechanical behavior at the local level
(nanoindentation) and the global level (shear testing) to relate
microstructure to performance
- study oxide formation at soldering temperatures and the
interaction of the fluxes during soldering using surface sensitive
techniques such as X-ray Photoelectron Spectroscopy
- Mechanical properties in Sn-Ag-Cu and other lead-free systems
have been characterized using a single, consistent technique:
- Several of the intermetallic compounds usually blamed for brittle
failure are actually fairly ductile at small scales.
- An indentation size effect has been identified for certain
- Reaction kinetics for Sn-Ag-Cu, Sn-Cu, and Sn-Ag alloys have been
- R.R. Chromik, R.P. Vinci, S.L. Allen and M.R. Notis,
Nanoindentation Measurements on Cu-Sn and Ag-Sn Intermetallics Formed
in Pb-Free Solder Joints, J. Mater. Res., 18 (9), 2003, p. 2251.
- S.L. Allen, M.R. Notis, R.R. Chromik, R.P. Vinci, Microstructural
evolution in lead-free solder alloys. Part I: Cast Sn-Ag-Cu eutectic,
J. Mater. Res., 19, 2004, pp. 1417-1424.
- S.L. Allen, M.R. Notis, R.R. Chromik, R.P. Vinci, D.J. Lewis, R.
Schaefer, Microstructural evolution in lead-free solder alloys. Part
II: Directionally solidified eutectic Sn-Ag-Cu, Sn-Cu and Sn-Ag alloys,
J. Mater. Res., 19, 2004, pp. 1425-1431.
- R.R. Chromik, R.P. Vinci and M.R. Notis, “Application of the
Nanoindentation Technique for Characterization of Intermetallics in
Pb-Free Solder Joints”, Proceedings of IMAPS Optoelectronics Conference
and Workshop, September 2004, Technical publication available at
- R.R. Chromik, D.-N. Wang, A. Shugar, L. Limata, M.R. Notis, and
R.P. Vinci, Mechanical Properties of Intermetallic Compounds in the
Au-Sn System, J. Mater. Res., 20 (8), 2005, pp. 2161-2172.
Portions of this work were performed collaboratively by
University, Penn State University, and the Visteon Corporation.
Support for Lehigh has been provided by:
The views and
conclusions contained in this document are those of the authors and
should not be interpreted as representing the official policies, either
expressed or implied, of the Army Research Office, Army Research
Laboratory, or the U.S. Government.
- the Pennsylvania Department of Community and
Economic Development, Contract No. 20-906-0015
- the U.S. Army Research Office
and U.S. Army Research Laboratory,
Cooperative Agreement Number DAAD19-02-2-0030.
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Last updated: August 2, 2005