Direct microwelding of dissimilar glass and Kovar alloy without optical contact using femtosecond laser pulses

In the current microwelding process using femtosecond (fs) laser between dissimilar materials, surface polishing and pressure assistance, so-called optical contact, are believed necessary. In this paper, direct welding of soda lime glass and Kovar alloy using a fs laser is investigated to overcome the limit of optical contact. The processing of fs laser welding is comprehensively studied by varying the laser power, welding velocity and the number of welding. The shear joining strength is as high as 2 MPa. The cross-section of glass-Kovar alloy joints, the elemental diffusion and the fracture behavior of welded joints were studied. The results show that the fs laser irradiates the surface of Kovar alloy, micron/nanometer-sized metal particles are generated. These particles perform the role as an adhesive part in the welding process. It is believed that the Si atoms diffuses to Kovar alloy from the glass and partially replaces the Fe2+ ions on the surface of Kovar alloy, indicating that the mixing and interdiffusion of materials have occurred during the welding process. Finally, the welded sample was tested and has excellent water resistance and sealing property. Furthermore, to justify that this method can be applied to other stack ups, the glass-copper, the glass-Al6063 and sapphire-ceramic are also welded together. This work greatly simplifies the fs laser microwelding process and promotes its industrial applications, such as optoelectronic devices, medical devices and MEMS.