A new interconnection technique for the attachment of sensors

For many applications, absolutely flat sensor surfaces are needed to bring the sensor's active structure into intimate contact with a specimen surface. To fulfil this requirement, a new interconnection technique is presented. It is based on funnel-shaped holes drilled into the substrate using a laser. After plating the contact pads with a solderable metallization, the funnel mouth serves as a reservoir for solder or conductive adhesive. This method allows formation of robust contacts between wires leaded-in from the rear side of the sensor substrate, rather than towering above its active surface. In this paper, we demonstrate the application of this method to the manufacturing of human skin moisture sensors. The laser drilling process, photolithography, thin film sputtering and etching techniques are described in detail with respect to peculiarities related to the funnel surfaces. In our case, the active sensor surface consists of a pair of comb-shaped molybdenum electrodes for the skin moisture measurement, and a molybdenum meander track for the measurement of the skin temperature. A good interconnection system was obtained with a solderable metallization system consisting of a double layer of NiCr-Au deposited on a base layer of Mo.