Temperature and thickness-dependent silver hillock generation mechanism and surface morphology nature of direct plated silver layers onto copper substrates

This study delves into the formation of hillocks on Ag surfaces, particularly those resulting from heat-induced processes. We investigate the Ag hillock generation mechanisms in direct Ag plating layers on copper (Cu) substrates, employing a combination of experimental and numerical approaches for comprehensive quantification. In the Ag layer system directly plated on Cu, the strain inside the grain system significantly increases as the temperature increases, but the energy level of the system drops due to the relaxation of the internal strain starting from a certain critical temperature. Namely, the Ag hillock growth mechanisms on Ag plated Cu substrate originated from the microstructural development with thermomechanical behaviors. Nevertheless, the Ag layer directly plated on Cu suffered Ag-Cu diffusion through the grain boundary due to heat, which contaminated the Ag plating surface. Hillock formation is possible even in an Ag layer directly plated on a Cu substrate, but Ag-Cu diffusion may be a factor that inhibits the development and growth of Ag hillocks. In this study, the major feature of the Ag hillock formation on the direct Ag layer plated on Cu substrate was systematically clarified in terms of the microstructures and mechanics of materials . • Possibility of hillock occurrence on the surface of Ag plated directly on Cu without a barrier. • Ag plating thickness and temperature dependence on hillock growth in Ag plating. • Identification of hillock formation mechanism in Ag plating that is different from sputtered Ag thin film.