The formation and growth characteristics of intermetallic compounds (IMC) at the interfaces in nanoscale and microscale thickness Cu-Sn-Cu sandwich structure (with different solder layer thicknesses of 130nm, 400nm and 1.5µm) during reflow soldering and aging were studied. The sandwich structure samples were fabricated by electro-plating, and followed by reflow and aging process. It was found that solder layers (Sn layers) might be totally consumed in the soldering and aging process when the thickness is sub-micron. For samples with solder layers of 130nm, we could even hardly find any evidence of the existence of Cu6Sn5 in the assoldered samples. For samples with solder layers of 400nm, both Cu6Sn5 phase and Cu3Sn phase were detected in the assoldered samples, and Sn as well as Cu6Sn5 was consumed in the aging period. When solder layer reached 1.5µm, Cu3Sn nucleated during aging but not the reflow process. Yet the overall thickness of IMC growth of these samples could not be described by the reported empirical parabolic curve of binary Cu-Sn couple's IMC growth, since the sub-micron solder layer was totally consumed by the growth of IMCs.