Eutectic wafer bonding is being investigated in industry and research due to the possibility to work at relatively low temperature and, at the same time, to obtain a metallic junction that offers greater reliability compared with other materials, such as polymers or glass[1]. In this work, electrodeposition of Sn-Cu alloy suitable for wafer bonding is studied using ethylene glycol as a solvent: this non-aqueous solvent is used for its promising properties, such as a wider electrochemical window in comparison with commercial solutions[2,3]. Several Sn-Cu solutions are tested with different concentrations of the two metal precursors and are characterized electrochemically, by cyclic voltammetry and linear sweep voltammetry. Deposition is performed both in direct and pulsed current mode, and the advantages of the latter are observed. The effects of pulse plating on the microstructure of the deposits are then investigated, by changing parameters as duty cycle, frequency and the shape of the pulses.

Figure 1 (see attachment): SEM morphologies of two samples deposited in direct current (a) and in pulsed current mode (b).

[1] C. C. Lee, C. Y. Wang, and G. S. Matijasevic, “A new bonding technology using gold and tin multilayer composite structures,” IEEE Trans. Compon. Hybrids Manuf. Technol., vol. 14, no. 2, pp. 407–412, Jun. 1991.

[2] H. M. Maltanava, T. N. Vorobyova, and O. N. Vrublevskaya, “Electrodeposition of tin coatings from ethylene glycol and propylene glycol electrolytes,” Surf. Coat. Technol., vol. 254, pp. 388–397, Sep. 2014.

[3] A. P. Abbott, A. I. Alhaji, K. S. Ryder, M. Horne, and T. Rodopoulos, “Electrodeposition of copper–tin alloys using deep eutectic solvents,” Trans. IMF, vol. 94, no. 2, pp. 104–113, Mar. 2016.