Four-Level Micro-Via Technology (4LµV) for ASIC Integration in Active Flexible Sensor Arrays

Abstract

Systems-in-foil with multi-sensor arrays require extensive wiring with large numbers of data lines. This prevents scalability of the arrays and thus limits the applications. To enable multiplexing and thus reducing the external connections down to few digital data links and a power supply, active circuits in the form of ASICs must be integrated into the foils. However, this requires reliable multilayer wiring of the sensors and contacts for chip integration. As an elegant solution to this, a new manufacturing process for multilayer wiring in polyimide-based sensor foils has been developed that also allows ASIC chips to be soldered. The electrical four-level micro-via connections and the contact pads are generated by galvanic copper deposition after all other process steps, including stacking and curing of polyimide layers, are completed. Compared to layer by layer via technology, the processing time is considerably reduced. Because copper plating of vias and solderable copper contact pads happens as the final step, the risk of copper oxidation during polyimide curing is completely eliminated. The entire fabrication process is demonstrated for six strain sensor nodes connected to a surface-mounted ASIC as a detecting unit for sensing spatially resolved bending states. Each sensor node is a full-bridge configuration consisting of four strain gauges distributed across interconnected layers. The sensor foil allows bending of +/- 120° without damage. This technology can be used in future for all kinds of complex flexible systems-in-foil, in particular for large arrays of sensors.

Development and Investigation of High-Temperature Ultrasonic Measurement Transducers Resistant to Multiple Heating–Cooling Cycles

“…An electroplating solution was made by mixing copper sulfate (150–250 g/L) and sulfuric acid (15–60 g/L). A 1–10 A/dm 2 current ( Figure 2 ) was applied for several minutes depending on the desired thickness [ 23 , 24 , 25 ]. All solutions were made of chemically pure reagents and bi-distilled water.…”

Liquid Metal and Carbon Nanofiber-Based Strain Sensor for Monitoring Gesture, Voice, and Physiological Signals

“…In the digital age of comprehensive health informatics, to realize continuous and real-time data collection throughout the day, lightweight and comfortable wearable sensors are indispensable . Soft and stretchable strain sensors, as one of the important elements in the family of wearable sensors, , have undergone development from traditional wire and/or foil strain gauges − to ultrathin-film-state strain sensors, for the purpose of making them respond simultaneously to the epidermic changes , and realizing precise detection . In addition, numerous contributions have been made to strain sensors by the use of newly developed materials, such as low-dimensional carbon materials, , biomass, , metal nanowires, , MXene fabric, , as well as hydrogels , and composites loaded with nanoconductive fillers, as well as the recently proposed crack-based strain sensors by imitating slit sensilla of arthropods .…”