Chain Length Dependence of SAMs-Assisted Copper Thermocompression Bonding
Direct metal thermocompression bonding is one of the key approaches used in creating interconnections in many heterogeneous devices. It has been reported that by coating a monolayer of alkanethiols on metallic surfaces such as gold or copper prior to bonding, the bonding temperature required for forming joints can be significantly reduced. In this paper, room temperature copper bonding is demonstrated successfully with the help of the organic monolayers. We also found that all alkanethiol- coated copper (CnH2n+1SH, at n = 6, 11, 18) exhibited superior bond strength (>25MPa) compared to that of the uncoated copper (<23MPa) at bonding temperatures from 25°C to 80°C. Further investigation shows that bond strength of copper joints increases with alkanethiol chain length (C18>C11>C6), which contradicts our previous finding in gold. We attribute this discrepancy to the difference in hardness between the two substrates.
Selin Teo, A. Q. Liu, H. Li and B. Tarik
L. Jia et al., "Chain Length Dependence of SAMs-Assisted Copper Thermocompression Bonding", Advanced Materials Research, Vol. 74, pp. 291-294, 2009