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Rare-earth additions to lead-free electronic solders

  • C. M. L. Wu
  • Y. W. Wong
Article

Abstract

The research in lead(Pb)-free solder alloy has been a popular topic in recent years, and has led to commercially available Pb-free alloys. Further research in certain properties to improve aspects such as manufacturability and long term reliability in many Pb-free alloys are currently undertaken. It was found by researchers that popular Pb-free solders such as Sn–Ag, Sn–Cu, Sn–Zn and Sn–Ag–Cu had improved their properties by doping with trace amounts of rare earth (RE) elements. The improvements include better wettability, creep strength and tensile strength. In particular, the increase in creep rupture time in Sn–Ag–Cu–RE was 7 times, when the RE elements were primarily Ce and La. Apart from these studies, other studies have also shown that the addition of RE elements to existing Pb-free could make it solderable to substrates such as semiconductors and optical materials. This paper summarizes the effect of RE elements on the microstructure, mechanical properties and wetting behavior of certain Pb-free solder alloys. It also demonstrates that the addition of RE elements would improve the reliability of the interconnections in electronic packaging. For example, when Pb-free-RE alloys were used as solder balls in a ball grid array (BGA) package, the intermetallic compound layer thickness and the amount of interfacial reaction were reduced.

Keywords

Rare Earth Solder Joint Solder Alloy Stress Exponent Solder Ball 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

The work described in this report was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, P. R. China [Project No. CityU 1026/04P].

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Copyright information

© Springer Science+Business Media, LLC 2006

Authors and Affiliations

  1. 1.Department of Physics and Materials ScienceCity University of Hong KongHong Kong SARP.R. China

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