Intermetallic phase formation in thin solid-liquid diffusion couples

• Published in: Journal of electronic materials 1994-08, Vol.23 (8), p.787-790
• Main Authors: Bartels, F., Morris, J. W., Dalke, G., Gust, W.
• Format: Article
• Language: English
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/BF02651374

Conducting joints with low fabrication temperatures and high thermal stability are useful in modern electronics. The potential use of intermetallic phases in making such joints is discussed. Thin interconnection layers that consist entirely of intermetallic phases were produced by joining planar Cu substrates that were coated with thin films of Sn. Thin layers (1-5 mu m) of intermetallic phases were produced at temperatures slightly above the melting temperature of Sn in a process similar to reflow soldering. Metallography and x-ray analysis were used to characterize the formation mechanism of the intermetallic. Cu dissolved into the liquid Sn by diffusion along narrow channels between grains of the growing Cu sub 6 Sn sub 5 intermetallic phase. Tensile tests were used to measure mechanical properties. The joint strength increased with reaction time. The joint failed in a ductile mode as long as unreacted Sn was present, but fractured along interphase boundaries when the joint was completely intermetallic.