Fluxless optical fiber attachment for hermetic MOEMS applications

Fluxless soldering is desirable for the hermetic packaging of micro-optoelectromechanical (MOEMS) systems, especially those used in harsh environments, or those that require very long shelf-life. An example of such a microsystem is a safe & arm (S&A) MEMS device that requires reliable operation over 20 to 30 years. For this application, degradation and out-gassing of the organic materials, such as those contained in fluxes and epoxies could result in the contamination and stiction of the moving microparts. In this paper we present simulation and experimental results of using a diode laser to attach and seal fiber optic feed-throughs to a kovar carrier package. In order to obtain reliable fluxless solder joints, certain environmental conditions namely, an inert and/or reducing gas environment needs to be present during the process. In addition, the solder and substrate surfaces must be sufficiently free of oxides and organic contaminants. Acceptable process parameters such as the laser power density, spot size, and duration, package geometry have been determined both experimentally and through simulation. It has been established that oxygen levels less than 0.04% (400 ppm) obtained inside a glove-box obtained using inert gas (100% N2 or 95%N2, 5% H2) is necessary to achieve adequate joints.