A new interconnection technique has been developed that allows versatile multiple strand connections between microsensors, sensor arrays, and chips designed for wire bonding. The new technique has been termed 'microflex interconnects' (MFI).Conventional wire bonding technique is commonly restricted to planar interconnects with a limited degree of freedom for placing microsystem components. The MFI technique has overcome this limitation by interconnecting microsystem components through custom designed flexible foils with embedded metallized conductors. The MFI foils may also serve as circuit substrates. This basic foil material is polyimide (Du Pont PI 2611)(1) or BCB2 which are patterned photolithographically. Platinum, gold or either conductive metals are sputtered or evaporated on the foil and patterned using lift-off technique. Several metallization layers can be embedded in the material. Pitch and shape of the MFI contact pads correspond to the one of the chips to be interconnected. A via hole is placed in the center of the MFI contact pads. MFI pads and chip pads are adjusted. Metal balls or wedges generate the electrical and mechanical contact through the vias between the chips and the MFI substrate. An commercial wire bonder is the only equipment needed to perform, the MFI method.The MFI technique was applied to bond standard CMOS integrated circuit (IC) bond pads with a width of 30 mu m and a pitch of 70 mu m to a 10 mu m thick MFI foil. The integration density of the MFI technique correspond to one of the flip-chip technology(3). Special advantages of the MFI technique are three-dimensional interconnects, the flexibility in design and shape, and easy visual inspection of alignment qualities. The MFI method is also suited for biomedical applications because all materials used are biocompatible.
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