Electrochemical Copper Deposition on Nanoscale-Sculptured Aluminum for Mechanically Stable Joints with Optimal Electrical and Heat Transport Properties

Abstract

Copper is a material with a very high conductivity per volume; therefore it is widely used in the industry for nearly every electric application. However, with respect to weight aluminum (due to its low density of 2.7 g/cm3) shows a significantly higher electrical conductivity than copper. For many lightweight applications, aluminum would be the preferred material, but it lacks for good technical solutions for forming easy to apply, corrosion resistant, highly conductive contacts to (other) metals, especially to copper. Many of these problems are related to the native aluminum oxide coating on all aluminum surfaces in contact to air. State of the art solutions for electrical contacting aluminum surfaces require high temperatures and/or high pressure, thus making them expensive and typically damage the surface near microstructure of the aluminum. In this abstract, we will discuss details of a room temperature technique, which allows for a mechanically stable, corrosion resistant, galvanic copper deposition on aluminum surfaces with extremely high interface conductivity for heat as well as for electrical current. This allows the application of standard bonding technologies for copper (e.g. soldering or using conductive glues) onto aluminum as a conducting material. The copper deposition technique contains three steps: 1. A special surface preparation, i.e. nanoscale-sculpturing (cf. [1]) which creates a low corrosive aluminum surface structure full of mechanical hooks, composed of 100 crystallographic facets. 2. A preconditioning step before galvanostatic copper deposition. 3. Galvanic copper deposition controlling the nucleation of copper islands within the hooking structure and the morphology of the growing copper layer. Due to the nanoscale-sculpturing, the deposited copper is mechanically stable bonded to the aluminum surface. Dependent on the demands for subsequent bonding applications, the galvanic copper deposition must be adjusted; e.g. for gluing, large parts of the hook like structure from the underlying aluminum surface should still exist after a thin layer of copper is deposited. In contrast, for soldering application, a robust and thick layer of copper is needed. How the nanoscale-sculpturing and the galvanic copper deposition can be adjusted to various application will be discussed in detail. [1] Baytekin-Gerngross, M., Gerngross, M., Carstensen, J. and Adelung, R. (2016). Making metal surfaces strong, resistant, and multifunctional by nanoscale-sculpturing. Nanoscale Horizons, 1(6), pp.467-472.