Stability of channels at a scalloplike Cu₆Sn₅ layer in solder interconnections

The thermodynamic stability of the solder channels at a scalloplike Cu₆Sn₅ layer formed between Sn-containing solders and Cu substrate was evaluated by studying the penetration behavior of the liquid solders into the grain boundaries of a Cu₆Sn₅ substrate. The orientational relationship between the grains of the Cu₆Sn₅ layer formed during reflow soldering was also analyzed using the electron backscattered diffraction technique. The results showed that liquid solders penetrate into the grain boundaries at an order of faster speed than the growth rate of the layer, which provided a direct evidence of thermodynamic stability of the channel.