PurposeThe purpose of this paper is to review traditional hermeticity test methods when applied to typical micro‐electro‐mechanical systems (MEMS) cavity volumes and to propose potential solutions.Design/methodology/approachStandards for traditional testing have been applied to typical MEMS cavity volumes and the resulting issues of range and sensitivity discussed. In situ test structures have been designed and fabricated with access to the internal cavities to allow characterisation of the structures as a function of pressure.FindingsThe ultra low leak rates necessary to guarantee hermeticity of MEMS cannot be measured using traditional methods. Optical test methods are possible although in situ test structures currently provide the greatest sensitivity. A portfolio of test techniques is required to allow accurate hermeticity testing of MEMS.Research limitations/implicationsThis paper provides a starting point for further investigation into several methods of MEMS hermeticity testing.Originality/valueThis paper provides a review of the limitations of traditional testing and proposals for future testing as the trend towards smaller volume packaging continues.

Glass frit packaging is a simple and robust method used for hermetic sealing of micro-devices. Conventional glass frit packaging processes rely on furnace heating where the entire package is heated to elevated temperatures, hence restricting the use of temperature-sensitive materials inside the package and generating problems in multi-stage packaging processes. The use of a laser as an alternative heat source offers the possibility of highly localized heating where the heat-input can be restricted to the joining area only. In this paper the clear benefits of combining glass frit packaging and localized laser heating are demonstrated. Two novel laser-based glass frit packaging processes for sealing of leadless chip carrier (LCC) packages in both air and vacuum have been developed. Full hermetic seals according to MIL-STD-883G are achieved in high yield processes where the temperature in the centre of the device is kept at least 230 °C below the temperature in the joining region.

This paper presents the limitations of the helium leak test when applied to typical MEMS packages. A novel closed-form expression is presented which allows the determination of the minimum cavity volume package that can be accurately tested using the helium leak test method in conjunction with a standard gross leak test. This expression can be used to find optimum test parameters for packages with cavity volumes greater than 2.6 9 10 -3 cm 3 . Hermeticity testing using FTIR and Raman spectroscopy are considered as potential methods to overcome the limitations of the helium leak test method.

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