Formation and growth of interfacial intermetallic layers in eutectic Sn-Ag solder and its composite solder joints

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Single shear lap joints were made by soldering two Cu substrates with eutectic Sn-Ag solder, and its composite solders containing FeSn/FeSn2 or Ni3Sn2 intermetallic particles introduced by an in-situ method. Ageing of solder joints was performed at 70, 100, 120, 150, 180 °C for 1400 h. The growth of the interfacial intermetallic compound (IMC) layers was characterized assuming diffusion-controlled growth kinetics. Effects of such FeSn/FeSn2 and Ni3Sn4 particulates on the IMC layer growth rate were extensively characterized. Composite solder joints in the fabricated condition formed thinner IMC layers compared to the corresponding non-composite solder joints. The Cu6Sn5 IMC layer grew faster at temperatures above 120 °C (T/T m=0.8), while growing slower at temperatures below 120 °C in composite solder joints. In-situ introduced FeSn/FeSn2 and Ni3Sn4 particle reinforcements in composite solder joints proved effective in reducing the overall growth of the interfacial Cu6Sn5 IMC layer only at lower temperatures. Composite solder joints exhibited slower growth of the Cu3Sn layer during ageing at all temperatures used in this study. Two different regions having different activation energies depending on the temperature were identified for the growth of Cu6Sn5 and Cu3Sn IMC layers. © 2000 Kluwer Academic Publishers