Advances in laser based joining processes of micro-devices using localised heating

Abstract

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...