Optical fiber packaging by lead (Pb)-free solder in V-grooves

Etched V-grooves along the [1 1 0] direction on (0 0 1) surface of Si wafers have been used to achieve high precision alignment between fibers in opto-electronic devices by epoxy-bonding. Nevertheless, the positioning of fibers using epoxy-bonding lacks long-term stability. We developed a novel technology of using metallic solder bonding instead of the organic epoxy-bonding. The challenge is because of the fact that solder does not wet SiO2 surface. To circumvent this problem, electron-beam evaporation was used to deposit a multi-layered metallic coating on the surfaces of fibers and V-grooved chips. Three types of coatings were investigated, and they are Ti/Au, Ti/Cu/Au, and Ti/Ni/Au. These metallic film coatings have good adhesion on the fiber and the V-groove. We utilized a low melting point Pb-free solder, eutectic 43Sn57Bi (in wt.%), with a melting point of 139 °C to bond an array of fibers to V-grooved chips. The mechanical and optical tests illustrated that we can achieve precision alignment of fibers by the soldering method and the bonded structure is stable at room temperature. The metallic solder bonding can be hermetic and it can isolate the optical device from ambient environment.