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In recent years various techniques have been developed for the manufacture of microsystems and other miniature optoelectronic devices. One aspect where there remains significant room for improvement is the packaging process. Standard packaging techniques involve heating whole devices to high temperatures, in some cases combined with strong electric fields, preventing the use of temperature-sensitive materials within the package and generating problems in manufacturing processes where a number of thermal process steps are carried out sequentially, when a later heating step can cause parts joined earlier to disassemble. Here we describe the successful application of laser-based joining for the packaging of such devices.

In this paper, we investigate the feasibility of using a laser as the heat source to drive a hermetic joining process based on a glass frit intermediate layer. The laser allows the necessary heat energy to be provided in a localized manner; important either as part of a multistage process, or to allow thermally-sensitive materials to be used inside the package. Our study includes an investigation of the impact of rough and grooved surfaces on the hermeticity and strength of the join, demonstrating the robust nature of the process, and its ability to allow feed-throughs to the center of package. Hermetic sealing is demonstrated, with leak rates of 10−9 mbar l s−1, satisfying the military standard MIL-STD-883G.

In recent years there has been significant interest in the development of new types of Micro-Electro-Mechanical-Systems (MEMS) and related micro-devices but the issue of packaging remains a problem in many cases, and is indeed a particular challenge for their commercialisation. Current hermetic bonding techniques involve heating the whole device to high temperatures, in some cases combined with strong electric fields. This prevents the use of temperature-sensitive materials within the package polymer and magnetic materials). We have therefore been developing alternative solutions based on the use of a laser as a truly localised heat source to drive an intermediate layer bonding process. In this paper we describe laser-based packaging of silicon to glass - materials commonly used in MEMS fabrication - on a wafer-level, where multiple devices are packaged on a single silicon wafer. The bonding is achieved by using a Benzocyclobutene intermediate layer. Previously we have demonstrated bonding of a simplified pattern of 5 individual packages on the same chip as a proof of principle. In this work we present packaging of more complex and more closely spaced patterns and the issues involved in such processes when using laser bonding.In recent years there has been significant interest in the development of new types of Micro-Electro-Mechanical-Systems (MEMS) and related micro-devices but the issue of packaging remains a problem in many cases, and is indeed a particular challenge for their commercialisation. Current hermetic bonding techniques involve heating the whole device to high temperatures, in some cases combined with strong electric fields. This prevents the use of temperature-sensitive materials within the package polymer and magnetic materials). We have therefore been developing alternative solutions based on the use of a laser as a truly localised heat source to drive an intermediate layer bonding process. In this paper we describe laser-based packaging of silicon to glass - materials commonly used in MEMS fabrication - on a wafer-level, where multiple devices are packaged on a single silicon wafer. The bonding is achieved by using a Benzocyclobutene intermediate layer. Previously we have demonstrated bonding of a simplified...

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.

In this paper we investigate and compare a laser-driven joining process with two different illumination conditions: (i) high speed scanning of a focused beam and (ii) reasonably uniform “flood illumination” of the whole sample. It is shown that the scanning beam not only avoids illuminating the central part of the device, but also provides more uniform heating of the area to be bonded than laser “flood illumination”. We demonstrate bonding of three different packages: (i) LCC (Leadless chip carrier) packages, (ii) AlN and (iii) LTCC (Low temperature co-fired ceramic) substrates to “top-hat” packages, using a scanned beam from a fibre-delivered high power laser diode array to cure an intermediate layer of glass frit. Standard leak testing demonstrates that all those samples have excellent hermetic sealing with leak rates at the level of 10−9 atm·cc/s.In this paper we investigate and compare a laser-driven joining process with two different illumination conditions: (i) high speed scanning of a focused beam and (ii) reasonably uniform “flood illumination” of the whole sample. It is shown that the scanning beam not only avoids illuminating the central part of the device, but also provides more uniform heating of the area to be bonded than laser “flood illumination”. We demonstrate bonding of three different packages: (i) LCC (Leadless chip carrier) packages, (ii) AlN and (iii) LTCC (Low temperature co-fired ceramic) substrates to “top-hat” packages, using a scanned beam from a fibre-delivered high power laser diode array to cure an intermediate layer of glass frit. Standard leak testing demonstrates that all those samples have excellent hermetic sealing with leak rates at the level of 10−9 atm·cc/s.

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.

One of the remaining issues in the fabrication of micro-devices, including MEMS, is the packaging process. Standard techniques involve heating the whole device to high temperatures, preventing the use of temperature-sensitive materials within the package (e.g. polymer and magnetic materials) and generating problems in manufacturing processes where a number of thermal process steps are carried out in sequence, when a later heating step can cause parts joined earlier to disassemble. In our previous studies we demonstrated that it is feasible to combine the benefits of intermediate layer bonding and laser heating to achieve packaging processes where the required high temperatures are highly localised. Previously only single chip packaging was presented and therefore in this paper we demonstrate solutions to the issues involved in laser-based wafer-level packaging, where many devices are packaged on a single silicon wafer. In this case our example is a silicon-glass package using a Benzocyclobutene intermediate layer – materials commonly used in MEMS fabrication. We also report on developments for packages requiring a moderate vacuum with long-term stability. Here a glass-frit based process using localised laser heating is described.One of the remaining issues in the fabrication of micro-devices, including MEMS, is the packaging process. Standard techniques involve heating the whole device to high temperatures, preventing the use of temperature-sensitive materials within the package (e.g. polymer and magnetic materials) and generating problems in manufacturing processes where a number of thermal process steps are carried out in sequence, when a later heating step can cause parts joined earlier to disassemble. In our previous studies we demonstrated that it is feasible to combine the benefits of intermediate layer bonding and laser heating to achieve packaging processes where the required high temperatures are highly localised. Previously only single chip packaging was presented and therefore in this paper we demonstrate solutions to the issues involved in laser-based wafer-level packaging, where many devices are packaged on a single silicon wafer. In this case our example is a silicon-glass package using a Benzocyclobutene intermedia...