A Novel Approach to Assembly and Interconnection for Micromachines.

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Current fabrication technology for microelectronics or micromachines is based on the surface micromachining techniques for the basic processing steps of silicon-LSI technology. However, fabrication of real intelligent microsystems requires not only substantial progresses in the micromachining technology but also the ability to integrate and assemble the microcomponents to get a requisite three-dimensional structure. The main drawback of the conventional bonding methods is their rather high process temperatures which exclude the use of less heat-resisting components or preprocessed devices.In this study we obtained a newly developed microassembly apparatus, in which microcomponents can be positioned precisely and bonded to each other via the SAB method at room temperature. The microassembly apparatus consists of two UHV chambers, one of which is used for the feed-through of the specimens which are mounted on a disc and transferred into the assembly chamber. A specimen is then picked up … More from the disc by a manipulator and held at a desired position above the other specimen which is set on a multi-axial stage of twelve degrees of freedom of motion. The desired bonding positions may be derived the combining operations of the manipulator and the multi-axial stage. Briefly, the manipulator is driven by a SMA (shape memory alloy) spring and the multi-axial stage is operated by eleven stepping motors and three piezo-acturators.The positions of the specimens are monitored by a SEM (scanning electron microscope) which is operated also in UHV conditions. The surface of the specimens to be bonded are then sputter-cleaned by Ar fast atom beam (FAB) irradiation of about 1.5keV for several minutes. After native oxide film on metal surface or contaminated surface layr is removed, they are brought into contact under a slight pressure. Since the FAB source is pumped differentially, the whole processes are going on at an UHV lower than 10^<-7> Pa at this time.We investigated on the microbonding of Sn solder (phi340mum) and Al or Cu plates by means of the SAB method at room temperature. The bond strength of Sn solder to Al or Cu reached as high as 40MPa.These interface structures were investigated by transmission electron microscopy (TEM). At interface between Cu and Sn, there is inter-layr of about 5nm, which is Cu_6Sn_5 intermetallic compound. At interface between Al and Sn, Al and Sn atoms bonded directry without inter-layr and lattice distortion. Less