Characterizations of laser transmission welding of glass and copper using nanosecond pulsed laser

In this study, we conducted an investigation into the heterogeneous bonding process of glass and copper using a nanosecond pulsed laser for laser transmission welding. Our research focused on examining various processing parameters and the influence of focal plane positions on bonding quality. To evaluate weld strength, we employed both pull-tensile separation force (PTSF) and shear-tensile separation force (STSF) measurements. The analysis of fracture and separation results encompassed detailed examinations of weld morphology, microstructure, elemental composition, and phase configuration. The results revealed that increasing the laser welding energy initially enhanced the weld strength until it reached a saturation point. This saturation point was attributed to the formation of voids or cracks, leading to residual stress within the weld zone due to non-uniform hot spots in the molten area during processing. Among the different focal plane positions tested, positioning it below the glass/copper interface yielded the highest weld strength. The maximum achieved bond strength was above 10 MPa, demonstrating the feasibility of cost-effective pulsed laser welding for copper-to-glass applications. Moreover, the weld strength obtained using STSF surpassed that of PTSF. This discrepancy arises from the fact that PTSF separation led to fractures at the weld seam-glass boundary, leaving the weld seam on the copper plate. In contrast, STSF resulted in separation along the weld-copper interface, leaving the weld seam on the glass sheet. In-depth analysis through SEM and EDS elucidated that Cu and SiO₂ underwent intra-mixing and inter-particle diffusion in the molten pool during welding. HR-TEM and SAED observations unveiled the presence of polycrystalline copper nanoparticles, copper oxides, and an amorphous Cu–O-Si region at the weld interface. This amorphous region significantly contributed to the robust bonding between copper and glass.