Characterization of hermetic wafer-level Cu-Sn SLID bonding

• Published in: 2012 4th Electronic System-Integration Technology Conference pp. 1 - 7
• Main Authors: van de Wiel, H. J., Vardoy, A-S. B., Hayes, G., Fischer, H. R., Lapadatu, A., Taklo, M. M. V.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.09.2012
• ISBN: 1467346454; 9781467346450
• DOI: 10.1109/ESTC.2012.6542150

A flux-less copper-tin (Cu-Sn) solid-liquid inter-diffusion (SLID) bonding process, providing a cost-effective hermetic vacuum sealing at wafer-level, has been investigated. Observations have been made indicating that the storage time of Cu-Sn plated wafers before bonding is critical with regard to voiding. Growth of the intermediately formed intermetallic compound (IMC), Cu 6 Sn 5 , was investigated as a possible cause. Room temperature aging of Cu-Sn plated wafers prior to bonding was performed as well as annealing of un-bonded Cu-Sn plated wafers. The presence of large Cu 6 Sn 5 and Cu 3 Sn crystallites which nearly depleted the Sn was observed by optical microscopy after annealing. If large Cu 6 Sn 5 grains from opposite contact planes meet at the bond interface, voids are predicted to be formed during the subsequent stages of liquid inter-diffusion and solidification. Implications on the Cu-Sn bonding strategy based on the results are presented.