Deformation Behavior of Asymmetric Direct Laser Interference Patterning Structures on Hot-Dip Tinned Copper

Understanding contact mechanics is essential for optimizing electrical and mechanical interfaces, particularly in systems where surface structuring influences performance. This study investigates the mechanical contact behavior of hot-dip tinned copper surfaces modified via Direct Laser Interference Patterning (DLIP). Asymmetric, line-like microstructures with varying periodicities (2-10 µm) and tilt angles (0°, 15°, 30°) were fabricated on both as-received and aged hot-dip tinned copper substrates. The resulting surfaces were characterized using confocal laser scanning microscopy and subjected to indentation testing under controlled loads. Contact mechanical calculations and finite element simulations were employed to determine critical values for plastic deformation onset and to access the real contact area. Results show that structural periodicity, tilt angle, and material condition significantly affect load-bearing capacity and deformation behavior. Notably, intermediate periodicities (e.g., 7.5 µm) on as-received material at 0° tilt exhibited the highest susceptibility to plastic deformation, while aged samples demonstrated improved mechanical stability due to the harder Cu₆Sn₅ surface layer, which forms directly after coating and grows during aging until it reaches the surface and no residual tin is left. These findings provide valuable insights into the design of structured contact surfaces for electrical applications, highlighting the importance of tailored surface morphology and material selection.