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Carol Handwerker - Research

Pb-Free Solders: Manufacturing and Reliability

In 1999, the European Union banned the use of Pb in electronics and electrical equipment offered for sale in the EU as of July 1, 2006. For the worldwide electronics industry this means that Pb-Sn eutectic solder can no longer be used to assembly components together into functional circuit boards. All products offered for sale as of that date must be assembled with Pb-free solder. A new international standard Pb-free solder alloy has been chosen based on the Sn-Ag-Cu system and many of the basic manufacturing and reliability issues associated with Sn-Ag-Cu have been resolved. However, Many application-specific issues require research to resolve, particularly for high reliability applications such as military, aerospace, medical device, and automotive electronics. Four current areas of Pb-free solder research are (1) Interdiffusion and phase transformations as circuit boards materials and components interact with Pb-free solders during high temperature circuit board assembly; (2) Manufacturing and reliability issues as Pb-free and Sn-Pb technologies are mixed during the transition to Pb-free assemblies; (3) The role of grain growth and stress relaxation on Sn-whisker formation in Pb-free thin films, a possible source of failure and short circuiting in Pb-free electronic assemblies, and (4) The relationship between performance in accelerated thermal cycling tests and reliability for specific applications. These four areas are of significant interest to the microelectronics industry and substantial collaboration with industrial partners is possible.

The EU Directive for the Reduction of Hazardous Substances (RoHS) leaves open the possibility that materials in addition to Pb, Cd, and Hg may be banned in the future for environmental reasons. A major gap in engineering and design knowledge is a clear methodology for assessing the life cycle environmental cost for particular technologies and products. Without such an agreed-upon methodology and some rational case studies, environmental decisions will continue to be made based on poor assessments, leading in some cases to unintended environmental consequences. Purdue University, through the Signature Area of Global Sustainable Industrial Systems, could play a significant role in integration of materials life cycle analysis into design, and in the promulgation of such concepts into manufacturing. The microelectronics industry has begun to address the question of how to define sustainability for the global manufacturing supply chains and global life cycles inherent in microelectronics.

Selected Publications

  • Experimental and thermodynamic assessment of Sn-Ag-Cu solder alloys, Moon, K. W., Boettinger, W.J.; Kattner, U.R.; Biancaniello, F.S.; Handwerker, C.A., Journal of Electronic Materials 29 [10] 1122-1136 (2000).
  • The effect of Pb contamination on the solidification behavior of Sn-Bi solders, Moon K.W., Boettinger, W.J., Kattner, U.R., Handwerker, C.A., Lee, D.J., Journal of Electronic Materials, 30 [1] 45-52 (2001).
  • Calculation of phase equilibria in candidate solder alloys, Kattner, U.R., Handwerker, C.A., Zeitschrift fur Metallkunde 92 (7) 740-746 (2001).
  • Reliability of Pb-Free Solders, C. A. Handwerker, D. A. Noctor, and G. Whitten, Environment-Friendly Electronics: Lead-Free Solders, Ed. Jennie S. Hwang, Electrochemical Publications, Isle of Man, British Isles, 2001, 566-589.
  • Mechanism of fillet lifting in Sn-Bi alloys, Boettinger, W.J., Handwerker, C.A., Newbury, B., Pan, T.Y., Nicholson, J.M., Journal of Electronic Materials, 31 (5) 545-550 (2002).
  • Recommended Practice Guide: Test Procedures for Developing Solder Data, Ed. T. A. Siewert and C.A. Handwerker, NIST Special Publication (SP), February 2003.
  • Major International Lead (Pb)-Free Solder Studies, C. A. Handwerker, K. Suganuma, E. de Kluizenar, and F. R. Gayle, Issues and Implementation of Pb Free Technology in Microelectronics, Eds. K. Puttlitz and K. Stalter, McGraw Hill/IEEE, 2004. Lead-free Solder Alloys: NEMI Recommendation (Cover Article), E. Bradley, C. Handwerker, J. Sohn, Circuits Assembly, January 2003.
  • NEMI Lead-Free Assembly Project: Comparison Between PbSn and SnAgCu Reliability and Microstructures, Carol Handwerker, Jasbir Bath, Elizabeth Benedetto, Edwin Bradley, Ron Gedney, Tom Siewert, Polina Snugovsky, John Sohn, Proceedings of Surface Mount Technology International, Chicago, September, 2003.
  • NEMI's Characterization of Lead-Free Alloy Applicable to Today's Commercially Available Alloys, A. Rae and C.A. Handwerker, Circuits Assembly, Vol. 15 [4] April 2004, p 20-25.
  • Materials Science Concepts in Lead-Free Soldering, C. A. Handwerker, U. R. Kattner, and K-W Moon, Pb-Free Soldering in Electronics – Science, Technology, and Environmental Impact, Ed. K. Suganuma, Marcel Dekker, 2004.
  • Transition Issues in the Conversion to Pb-Free Solder, C.A. Handwerker, Circuits Assembly, Vol. 16 [4] March 2005.