Joining of Transparent Substrates Through a Combination of Laser-Induced Forward Transfer and Laser Micro-Welding

Abstract Transparent materials like glass are widely used in consumer electronics, optoelectronic devices, electrical insulation, and lab-on-a-chip devices due to their superior physical and chemical stability and high optical transparency. In recent years, significant effort has been directed toward achieving high-precision laser-based joining of optically transparent materials. Due to the laser's poor absorption in transparent glass substrates, thin-film absorptivity coatings are typically used to enhance absorption and facilitate welding. However, this reduces the optical transparency of the processed zone. To avoid this, we selectively coated two quartz substrates with an absorptive film via laser-induced forward transfer (LIFT) and then welded them using the same laser source. This enabled the successful welding of the two quartz plates while maintaining the transparency of the unprocessed zone. Initially, the substrate was spin-coated with copper nano ink, serving as a transfer layer(donor). A pulsed laser beam was directed perpendicularly onto the donor, which precisely transferred a layer of material to a specific location on the surface beneath it (the receiver). The donor was then replaced with a fresh, uncoated quartz substrate. The laser was scanned over the previously transferred zone. High laser fluence caused the melting of the interface and enabled successful welding. The shear strength test also shows an excellent shear strength of 57.04 MPa ± 7.19 MPa. Thus, a combination of LIFT and laser micro-welding techniques provides a low-cost, practical solution for precise, selective laser welding of transparent materials.