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Fraunhofer Group for Microelectronics

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10.03.2010 Category: Fraunhofer ENAS, Technology, Issue 38

Reactive bonding solves temperature problems

Microelectronic and micromechanical systems are being packaged ever closer together as part of system integration. This leads to more and more problems during manufacturing process, because high joining pressures and differences in temperature can damage very sensitive devices. Researchers at Fraunhofer ENAS have now found a solution: A new process makes it possible to join parts together at room temperature.

 

High joining pressures and temperature differences during manufacture cause thermomechanical stress. This can damage or even destroy temperature-sensitive materials and integrated electronics. Different materials undergo thermal expansion at different rates, which generates great stress within the systems. For this reason, new low-temperature wafer-level bonding processes, which operate at temperatures below 300 °C, are becoming increasingly important.

A hot idea

Local heating of the joining parts is a very promising method of working at low processing temperatures. This new technology, which uses an internal heat source for joining, is known as “reactive bonding.” It is based on the use of reactive multilayer systems, mostly in connection with additional layers. The heat needed for the joining process is generated by a self-propagating chemical reaction within the system. To catalyze the reaction, all that is needed is a single low-energy impulse, such as that produced by a laser. The most important advantage of this technology is that the heat generated is localized to the bonding interface. This ensures that the components are not exposed to high temperatures over a large area. The technology also offers new ways of joining temperature-sensitive materials with different thermal expansion coefficients, such as metals and polymers, without causing thermal damage. The components are joined at room temperature and, if necessary, a hermetically sealed joint can be produced – temperature problems in joining processes have become a thing of the past.

From nano to micro

The Fraunhofer Research Institution for Electronic Nano Systems ENAS focuses ist research work not only on the use of commercially available reactive films, but also on an application for joining whole wafers. The researchers have succeeded in joining different MEMS and in depositing layered systems with individual layer thicknesses in the range of a few nanometers directly onto wafers. The micro- and nanostructures of the systems were then characterized and evaluated in cooperation with the Fraunhofer Institute for Mechanics of Materials IWM in Halle. The results show that temperature-sensitive microsystems – such as a silicon infrared emitter on a TO base – can be joined based on the nanoscale reactive multilayer system. Furthermore, the systems that were deposited directly displayed the possibility of initiating a reaction in very thin layer systems. This reaction could be used to generate the heat for the joining process. This opens up many potential applications for this wafer-level bonding process.

Contact:

Maik Wiemer
Phone +49 371 45001-233
maik.wiemer(at)enas.fraunhofer.de
Fraunhofer Institute for Electronic Nanosystems ENAS
Technologie-Campus 3
09126 Chemnitz
Germany
www.enas.fraunhofer.de