Design and Fabrication of Micro and Nano Surface Structures for Enhancing Adhesion Strength of Metal-Polymer Interface Using Femtosecond Laser Treatment

Abstract

Micro- and nano-scale structures on material surfaces are an effective and practical way to increase adhesion strength. In this study, the effects of micro-and nanostructures on the adhesion strength between copper and an encapsulating mold compound were investigated. The shape of the microgrooves on the copper surface was designed based on fracture mechanics theory, and the effect of laser-induced periodic structure surface (LIPSS) formation on the microgroove was investigated using finite element analyses. The designed surface profiles were fabricated using femtosecond laser treatments, and the adhesion strength between copper and the EMC was evaluated using button shear tests. The obtained results show that, by forming a deep microgroove, the adhesion between the copper and the EMC was improved owing to the anchor effect. However, it was found that there was a limitation in the aspect ratio between the pitch and depth of the microgroove for enhancing the adhesion strength. The formation of LIPSSs on the mountaintop of the microgroove was very effective, because LIPSSs suppressed the shear deformation of the EMC and interface delamination. Based on these findings, combining micro- and nano-scale surface structure formation with femtosecond laser treatments is an effective and eco-friendly method for improving adhesion strength.

Keywords: Micro and nano surface structures, Surface treatment, Adhesion strength, laser, LIPSS, Copper