Characterization of the reaction process in diffusion-soldered Cu/In-48Sn/Cu joints

SOMMADOSSI S., GUST W., MITTEMEIJER E.J.

MATERIALS CHEMISTRY AND PHYSICS

Año: 2002 vol. 77 p. 924 - 929

0254-0584

This work describes a Pb-free solder alternative for the interconnection technology and its implementation in a diffusion soldering technique: In–48 at.% Sn solder (eutectic alloy), with a melting point of 120 ºC. The system proposed has the advantages of both traditional soldering and diffusion bonding, i.e., good joint filling, high service temperature, and good mechanical properties. The diffusion reaction processes in Cu/In–48 at.% Sn/Cu joints were investigated between 180 and 400 .C. Electron microprobe analysis revealed the presence of one or two intermetallic layers in the interconnection zone: a layer of the η phase below 200 .C, and layers of the η and ζ phases above 200ºC. The η and ζ phases form through a solid–liquid and a solid–solid diffusion reaction, respectively. Below 200ºC the η phase exhibits two different morphologies: large coarse grains at the η /(originally liquid)In–48 at.% Sn interface and a fine-grained region at the Cu/η interface. The thickness of the ζ layer shows a constant growth rate (linear growth) at constant temperature. The temperature dependence of the growth rate constant of the ζ layer is described by an Arrhenius relationship with an activation energy equal to 121 kJ/mol and a pre-exponential factor of about 57 m/s.