Authored By:
Abhilaash Ajith Kumar, Werner Hügel, Ph.D.
Robert Bosch GmbH
Schwieberdingen, Germany
Summary
Ever increasing need for miniaturization and high-density electronics, leads to higher intermetallic (IMC) phase/solder ratio affecting the ductility of the solder joint. The diffusion behavior and growth of intermetallic (IMC) phases of Cu-Sn system is studied through isothermal aging over wide range of temperature from 398K to 473K. Cu-Sn binary couples, prepared by electroplating Sn over bulk Cu, are aged at 398K, 423K, 453K and 473K for various times to investigate the microstructural development and growth kinetics of the IMC phases.
In-house developed algorithm was used to detect and quantify the Cu6Sn5 and Cu3Sn morphology from electron microscopy images. Considering the narrow compositional range and interdependent growth/dissolution of the two IMC phases, Wagner’s method is used to evaluate the integrated interdiffusion coefficients based on the measured IMC thicknesses. The activation energies and the diffusion constants of the Cu6Sn5 and Cu3Sn IMC phases have been calculated from the integrated interdiffusion coefficients.
Conclusions
The following conclusions are obtained from this work regarding the solid-state diffusion in rolled Cu – electroplated Sn system.
- Microstructural investigation revealed the presence of cracks along the grain boundaries of Cu6Sn5 and at the interface between Cu3Sn|Cu6Sn5 at both low and high temperatures after isothermal aging. This can lead to early failure of the solder joint.
- Integrated interdiffusion coefficients and activation energies for Cu6Sn5 and Cu3Sn have been calculated in this study.
- The lower activation energies of Cu6Sn5 and Cu3Sn confirms grain boundary diffusion growth of IMC phases between 398K – 473K.
- Fine grains in rolled Cu substrate enhances relatively the growth of Cu3Sn and results in overall lower total IMC thickness at the interface between Cu and Sn.
Initially Published in the SMTA Proceedings
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