Solid-state microchip laser bonding by a low temperature epoxy-free and flux-less process

Epoxy free bonding is decisive to improve reliability of optoelectronic devices using active components such as laser diode. Therefore soldering is usually preferred as bonding technology but it often needs components metallizing, heating over 140°C and liquid or gas fluxing which may let some corrosive residues. Thus soldering cannot be widely used on optical microchip components. Working on solid-state microchip laser bonding in a project called NANOPACK supported by the French research ministry, we have developed low temperature epoxy free bonding technology. The microchip laser is bonded onto a submount by thermocompression at low temperature and moderate relative pressure using an indium foil to form the adhesive joint. This technology uses both a unique property of indium to wet and to bond to certain non-metallics such as glass, quartz, and various metallic oxides, and fluxless soldering of indium with gold by solid-state interdiffusion bonding or solid-liquid interdiffusion bonding. This way, mean bond strength about 300 g/mm² has been obtained for 2 mg chip with very good resistance to thermal aging. This epoxy free technology offers a real alternative for bonding non-metallic components which cannot stand usual soldering processes. Moreover, as it is a fluxless process, this technology is very attractive to hermetically seal lids under controlled atmosphere.