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Zn-rich CuxZn(1−x) alloy films (60–88 at% Zn) are grown in a pyrophosphate-based bath via potentiostatic deposition as a precursor for the synthesis of nanoporous Cu. Voltammetric studies show a selective negative shift in the reduction potential of Cu after its complexation with pyrophosphate, allowing for co-reduction of Cu and Zn at similar potential ranges. Anodic stripping characterization reveals a distinct three-stage alloy dissolution behavior that enables the estimation of the alloys’ compositions. Moreover, a systematic study has been done to determine the optimal conditions for Cu–Zn electrodeposition routines at current efficiency of 63%–73% with precise control over the elemental composition and morphology of the alloy. Scanning electron micrographs reveal highly crystalline and uniform alloy deposits, while energy dispersive X-ray spectroscopy results suggest tunability of the alloys’ elemental composition by simple adjustment of the precursor Cu2+:Zn2+ ratio in the deposition bath at the optimized potential of −2.0 V vs MSE. CuxZn(1−x) alloys of similar elemental composition and morphological quality were also electrodeposited on Cu and glassy carbon substrates. Finally, X-ray diffraction patterns of the electrodeposited alloys reveal the presence of CuZn5 and Cu5Zn8 intermetallic compounds that represent brass alloys in the composition range of interest.

Conspectus Nanostructured copper-based materials have emerged as a new generation of robust architectures for realizing high-performing and reliable interconnection in modern electronic packaging. As opposed to traditional interconnects, nanostructured materials offer better compliance during the packaging assembly process. Due to the high surface area-to-volume ratio of nanomaterials, they also enable joint formation by sintering through thermal compression at much lower temperatures compared to bulk counterparts. Nanoporous Cu (np-Cu) films have been employed in electronic packaging as materials that facilitate a chip-to-substrate interconnection, realized by a Cu-on-Cu bonding after sintering. In this Account, we discuss the use of self-supported np-Cu films for low-temperature joint formation. The novelty of this work comes from the incorporation of tin (Sn) into the np-Cu structure, thus ensuring lower sintering temperatures with a goal of producing Cu–Sn intermetallic alloy-based joints between two Cu substrates. The incorporation of Sn is done using an all-electrochemical bottom-up approach that involves the conformal coating of fine-structured np-Cu (initially formed by dealloying of Cu–Zn alloys) with a thin layer of Sn. This Account provides insight on existing technologies for using nanostructured films as materials for interconnects as well as the optimization studies for the Sn-coating processes as a new alternative approach. The applicability of the synthesized Cu–Sn nanomaterials for low-temperature joint formation is also discussed. To realize this new approach, the Sn-coating process is administered by a galvanic pulse plating technique, which is optimized to preserve the porosity in the structure with a Cu/Sn atomic ratio that allows for the formation of the Cu6Sn5 intermetallic compound (IMC). Nanomaterials obtained using this approach are subjected to joint formation by sintering at temperatures between 300 and 200 °C under 20 MPa pressure in forming gas atmosphere. Cross-section characterization of the formed joints postsintering reveals densified bonds with minimal porosity that consist predominantly of the Cu3Sn IMC. Furthermore, these joints are less prone to structural inconsistencies compared to existing joints formed using purely np-Cu. The results presented in this Account provide a glimpse into a facile and cost-effective approach for synthesizing nanostructured Cu–Sn films and illustrate their applicability as new interconnect materials.

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