Coarsening kinetics of Ni3Sn4 scallops during interfacial reaction between liquid eutectic solders and Cu/Ni/Pd metallization

The thickening and radial growth kinetics of Ni3Sn4 scallops formed during interfacial reaction between liquid eutectic solders and electroplated Ni/Pd metallization scheme on Cu substrate is studied. Selective etching of solder revealed three-dimensional morphology, and the dynamical phenomena,such as faceting, competitive growth, and coalescence of Ni3Sn4 scallops during interfacial reaction. The growth kinetics of the N3Sn4 scallops in the submicron length scale was analyzed using an Arrhenius-type of equation. Both kinetics exhibited nonparabolic behavior with the time exponent greater than three. The thickening of the Ni3Sn4 layer during interfacial reaction was accompanied by the concomitant coarsening of the scallops. The coarsening kinetics during early stages of interfacial reaction was characterized by (i) a temporal law with the time exponent greater than three, (ii) a decrease in the average number of scallops per unit volume with reaction time, and (iii) an increase in the standard deviation of the normalized size distribution with reaction time. The temporal laws for growth kinetics are discussed in terms of the effects of characteristic microstructural length scale and the existing coarsening theories. Among the coarsening theories, both the temporal law and the characteristics of radial size distributions were found to be consistent with the predictions of a recent Monte Carlo simulation of liquid-phase sintering in a two-phase system where the volume fraction of the second phase was very high. (C) 2000 American Institute of Physics. [S0021-8979(00)08923-4].