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Laser-based micro-bonding of VCSELs using arrayed beams from a fiber laser

We demonstrate a laser-based micro-bonding method for Vertical Cavity Surface Emitting Lasers (VCSELs) that enables practically sufficient joint strength, while securing the output power before bonding. VCSELs have great potential for optical interconnects because of their low threshold current and high-speed modulation capability. As for packaging of VCSELs, flip-chip bonding (FCB), among others, has been investigated because it facilitates the coupling of laser emission into fibers and waveguides. Conventional schemes for FCB, however, entail thermo-compressing stages and therefore the thermal and mechanical stresses involved are prone to cause defects in the lasing media, leading to quality defects. To overcome this problem, we have come up with a modified FCB method that can reduce such stress by employing laser irradiation to efficiently heat joints minimizing heat-affected regions. A micro-bonding system used in the experiments has an infrared fiber laser for heating, a diffractive beam splitter for parallel processing, a mounting head, and a slider for precise alignment and translation. VCSEL pads are kept in contact with counter pads on a substrate with AuSn solder placed between them. The split and focused beams by the element are guided to strike the joining points through the substrate, heating and melting the solder to attain a tight joint.