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|Scalable hybrid microelectronic-microfluidic integration of highly sensitive biosensors|
|Keywords: Microelectronic-microfluidic packaging, Fan-Out Wafer Level Packaging, Point-of-Care devices|
|The increasing distribution and acceptance of Point-of-Care devices creates the need for disposable highly sensitive biosensor devices. Specialized microelectronic sensor chips combining superior sensitivity compared to paper strips and better miniaturization potential, production scalability and readout simplicity compared to optical systems are emerging from science to application. Packaging of these sensors into a disposable component needs to comprise electronic connection as well as sensor-to-fluid exposure and the respective interfaces to the “macro world”. Reaching feasible costs for such integrated hybrid microelectronic-microfluidic components is possible by saving highly expensive silicon substrate area and place the non-active functionality such as electronic and fluidic wiring onto cheaper substrates. Here we present two packaging technologies addressing different product requirements: On the one hand we developed an adapted Fan-Out Wafer Level Packaging technology to assemble miniaturized active silicon components such as biosensors together with microfluidic functionality. Exemplarily we packaged graphene FETs considering their functionality and the biocompatibility of the process steps. By using microelectronic production equipment and avoiding slow and expensive serial processing, costs for such devices can be ultra-low at high volumes. During the process sequence, the silicon chips are firstly placed face-down on a double sided adhesive tape and are encapsulated by a compression molding process. This leads to a so called “reconfigured polymer wafer” comprising hundreds to thousands of the active chips with an exposed active surface, surrounded by polymer mold compound. The Sensor-IC pads are connected by metallization and lithography processes; forming a redistribution layer (RDL) and are routed onto the non-active backside of the polymer wafer by Through Mold Vias (TMV). There they can be contacted by connectors, sockets or pogo-pins. After electrical routing, the microfluidic element is formed on the flat surface of the polymer wafer by dry resist lamination and lithographic structuring. Finally, the polymer wafer can be diced into fully packaged microelectronic-microfluidic devices. During the processes the delicate active sensor surface is covered with protection layers, which can be removed without residues after packaging. All processes are scalable to typical wafer sizes (Ø 200 mm / 300 mm) and even full PCB panel size (610 x 460 mm²). On the other hand we developed a chip in PCB technology to assemble biosensors with mechanically sensitive structures avoiding the mechanically challenging compression molding process. Exemplarily the process is demonstrated with MEMS considering their functionality, especially their mechanical sensitivity, and the biocompatibility of the process steps. By using microelectronic production equipment, also here cost for such devices can be very low at high volumes. Process flow starts with the milling of cavities slightly larger than the MEMS dies into a PCB, which already carries the electrical wiring. The PCB is attached to a thermal release film and the MEMS are placed into the cavities, the microfluidic side facing towards the adhesive tape. The gap between the chips and the PCB cavity is filled with an adequate flexible adhesive yielding, after release, a PCB-sensor combination with a smooth planar surface for attaching the microfluidic. The 3D printed microfluidic is attached with a laser-cut double-sided adhesive. The electrical connection of the MEMS to the PCB is done with wire bonds protected by a polymer cap on the other (electrical) side. On the PCB they can be contacted by connectors, sockets or pogo-pins. In summary this paper presents the development of two process dedicated flows that allow the packaging of two sensor variants by using microelectronic packaging processes suitable for cost effective medium to high volume manufacturing. Both sensor packaging process variants have been validated by actual sensor embedding and functional testing in cooperation with sensor developers.|
Technical University of Berlin, Berlin, Germany