Structure-property relationships of Au films electrodeposited on Ni
- PDF / 2,384,681 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 21 Downloads / 170 Views
P2.8.1
Structure-property relationships of Au films electrodeposited on Ni C. San Marchi, N.R. Moody, M.J. Cordill**, G. Lucadamo, J.J. Kelly, T. Headley*, N. Yang Sandia National Laboratories, Livermore, CA 94550 *Sandia National Laboratories, Albuquerque, NM 87185 **University of Minnesota, Minneapolis MN 55455 Thin gold films and coatings on metal have long constituted an important technology for the microelectronics industry and will continue to be important for microdevices such as contact springs. The properties of these materials may be highly processing dependent, particularly when the gold is deposited by electrochemical means. In this study, we characterize gold electrodeposited on Ni substrates from two bath chemistries: hard Au sulfite with proprietary hardening additive and soft Au cyanide. TEM and SEM show that the bath chemistry alters the microstructure and the resulting surface of the electrodeposits. Nanoindentation techniques were used to determine the elastic and plastic properties of the Au electrodeposits as a function of the specifics of processing. Soft Au electrodeposits have a grain size of on the order of 300 nm and a hardness of about 1 GPa. Hard Au electrodeposits produced from the sulfite bath feature grain sizes as small as 30 nm, some twinning, and fine porosity uniformly distributed both within the grains and at grain boundaries. The hardness is about 2 GPa, approaching the hardest values reported for sputtered gold films. The effect of the hardening agent on the microstructure of electrodeposits from the Au sulfite bath was also investigated and found to significantly refine the grain size at concentrations of at least 4 mL/L, although little additional refinement was found at higher concentrations. INTRODUCTION Au electrodeposits are ubiquitous in the microelectronics industry serving numerous technical needs [1-2]. Pure or soft Au deposits are used for their high electrical conductivity, for corrosion resistance and for joining. Soft gold easily deforms, as the name implies, and while useful for bonding and joining, for contact applications hard gold is preferred for improved wear resistance. Hard gold is typically achieved with the addition of transition metal complexes and result in very fine-grained microstructures. Paradoxically, the fine grain size results in a fast diffusional conduit for transporting the transition metals to the free surface where they oxidize and increase electrical contact resistance. As localized heating is common in electrical contacts, especially at high current densities, thermal stability is an important consideration for transition metal-hardened Au electrodeposits and for thin Au electrodeposits on transition metals [3]. In this study, the microstructure and basic mechanical properties (modulus and hardness) of Au electrodeposits from Au cyanide and Au sulfite bath chemistries are compared. In addition, the effect of a proprietary hardening additive on the character of the Au sulfite electrodeposits is investigated. EXPERIMENTAL DETAILS Two basic
Data Loading...
