Localised laser joining of glass to silicon with BCB intermediate layer |
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Authors: | Qiang Wu N Lorenz D P Hand |
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Affiliation: | (1) Applied Optics and Photonics Group, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK;(2) Photonics Research Centre, School of Electronic and Communications Engineering, Dublin Institute of Technology, Kevin Street, Dublin 8, Ireland |
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Abstract: | The use of a laser to provide localised heating is an ideal solution to the problem of packaging micro-electro-mechanical-systems
(MEMS) whilst maintaining a low device temperature to avoid changes in temperature-sensitive materials in the device. In this
paper we present localised laser bonding of glass to silicon (normally used as the MEMS substrate) by using a fibre-delivered
high power laser diode array to cure an intermediate layer of the thermosetting polymer Benzocyclobutene (BCB). In our experiments,
we use two techniques to realise localised heating: one is to use an axicon together with a conventional positive lens to
generate a ring focus; the other is to use a scanning focused laser beam. In both cases localised cooling is required to confine
the elevated temperatures to the bonding area. Finite Element (FE) simulation indicates that both techniques should keep the
temperature in the centre of the package to approximately that of the ambient environment (300 K) during the process. However,
experiments show that the temperature in the centre of the package rises to a value of around 500 K, likely due to poor contact
between silicon and cooling sink. Experimentally, we confirmed that either technique can be used to obtain excellent bonding
of glass to silicon with leak rate at a level of 10−10 mbar l s−1, whilst keeping the centre of device at a lower temperature. |
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