Compact modular assembly and packaging of multi-substrate microsystems (WIMS cube).

Abstract

This research has developed a new approach for the assembly of microsystems consisting of multiple substrates containing circuits, sensors, and actuators in a reworkable and modular fashion. The microsystem dice are placed inside a cube (the WIMS -Wireless Integrated Microsystems- Cube). They are therefore self-aligned and stacked on top of one another, and are separated using non-conducting elastomer layers. Electrical/fluidic signal transfer between dice is achieved in one of two ways. The first method uses rows of integrated active flexible cables that are attached to the cube walls and actuated during assembly, row-by-row, to connect to the dice. The second method uses passive flexible cables integrated with separate connector dice that are interleaved between device dice inside the cube. In both methods, flexible cables make pressure contacts to microsystem dice, thus forming a mechanical connect/disconnect system for electrical/fluidic signals. A new actuation mechanism based on thermomagnetic effect was discovered and used for active flexible cables. In this actuation method, deflection caused by electromagnetic actuation can be increased by utilizing the softening of the cables due to heating. Thus, large deflections can be obtained at lower current levels. Thermomagnetically actuated 1mm x 1.3mm cables deflected 820-905mum with two stable positions in a 0.1T magnetic field and with a maximum power of 41.9mW. The stress characterization of the deposited layers and optimization of the residual stress of the stack of layers were also conducted in order to achieve flexible cables with desired bending characteristics. A process for forming a complete Cube with integrated electrical/fluidic connector cables and for assembling the entire microsystem was developed and WIMS Cube prototypes that are 5mm and 10mm on a side were fabricated using silicon technology to demonstrate the feasibility of this approach. The fabricated WIMS Cubes with integrated Parylene cables were tested for reliable pressure-contact electrical connections. Electrical contact resistances as low as 4.2O and 1.9O were achieved per passive electrical connectors and per two pressure-contact connections of active flexible cables, respectively. Reliability was demonstrated by electrically connecting and disconnecting the passive flexible cables ∼10 times. Tests on fluidic connectors were not performed.