Journal of Electronic Materials

, Volume 37, Issue 1, pp 102–109 | Cite as

Mechanical Size Effects in Miniaturized Lead-Free Solder Joints

  • Peter Zimprich
  • Usman Saeed
  • Agnieszka Betzwar-Kotas
  • Brigitte Weiss
  • Herbert Ipser
Open Access
Article

Future reliability and quality control of microelectronics will greatly depend on a detailed understanding of the complex mechanical and thermal properties of miniaturized lead-free solder joints. Therefore, the question of the occurrence of size effects or dimensionally induced constraints, which could change the mechanical properties of solder joints in small dimensions dramatically, has become the focus of investigation. In this study we investigated the influence of decreasing gap size on the tensile, shear, and stress relaxation behavior of solder joints to investigate the occurrence of size effects and dimensionally induced constraints, which could change the mechanical properties of solder joints significantly in micrometer dimensions. Residual stresses might remain in the solder joints during high-temperature dwell in thermomechanical fatigue. Model solder joints (Sn3.5Ag/Cu) of rectangular shape with gap sizes varying between 25 μm and 850 μm were prepared by reflow soldering to achieve near-industrial soldering processing. Scanning electron microscopy was used for analyzing the microstructure and the complex modes of fracture and crack propagation in the solder interconnect. The observed tensile behavior can be interpreted in terms of an existing theory for brazed joints to complement finite-element analysis that is usually used for a description of these phenomena.

Keywords

Lead-free solder joints mechanical size effects mechanical constraints tensile test shear test stress relaxation reliability 

Notes

Acknowledgements

This research is a contribution to the European COST Action 531. Financial support from the Austrian Science Foundation (FWF) under Project No. P-17346 is gratefully acknowledged. The authors thank D. Vogel and A. Gollhardt of the Institute for Microintegration and Reliability (IZM Berlin) for their support using the SEM for fracture monitoring, data interpretation, and helpful discussions; they also thank Ms. A. Ziering for the preparation of the solder joints.

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Copyright information

© TMS 2007

Authors and Affiliations

  • Peter Zimprich
    • 1
  • Usman Saeed
    • 2
  • Agnieszka Betzwar-Kotas
    • 1
  • Brigitte Weiss
    • 1
  • Herbert Ipser
    • 2
  1. 1.Faculty of PhysicsUniversity of ViennaViennaAustria
  2. 2.Department of Inorganic Chemistry-Materials ChemistryUniversity of ViennaViennaAustria

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