Characterization of MEMS-on-tube assembly: reflow bonding of borosilicate glass (Duran®) tubes to silicon substrates

Reflow bonding of borosilicate glass tubes to silicon wafers is a technology which has significant potential for microfluidic applications. The borosilicate glass tubes are designed to be used as an interface and package for wafer-level microfluidic devices. The strength of the resulting package has been tested by pressurizing it to failure. Failure occurred in the glass and the silicon adjacent to the bond, rather than along the bond itself. The bond formed is hermetic. The only leakage when testing the hermeticity of these bonds over a period of 1 month was due to gas diffusion through the glass. An unintended aspect of the heat treatments used for the reflow bonding was surface crystallization of the glass arising from heterogeneous nucleation and growth of cristobalite crystals. The bulk of the borosilicate glass remained unaffected by crystallization. For sufficiently large cristobalite crystals, microcracking occurred on the tube surface. Pressure test results indicated that the microcracking is not detrimental to the viability of this joining technology for microfluidic interconnections.