AEROSOL JET AND INKJET PRINTING OF ELECTRICAL INTERCONNECTS FOR DIE LEVEL PACKAGING OF CUSTOM MEMS DEVICES

In this study we propose an alternative, lowcost packaging method using both inkjet and aerosol jet printing to fabricate functional interconnects for custom die-level packages assembled on Printed Circuit Boards (PCB). Our process involves manufacturing of the stacked structure with insulating and conducting layers, fabricated using inkjet, and aerosol jet printing, respectively. In the first part of the study, we characterized UV adhesive deposition on the standard resin coated PCB, with the help of a Nordson EFD Pico Pulse drop on demand inkjet printer. This was done in order to acquire the optimal parameters necessary for the fabrication of an insulating layer with a thickness around 100 mu m. In the second part of our study, we developed precise printing of silver conducting lines using OPTOMEC Decathlon, an aerosol jet printer, which enables realization of structures with features as small as 50 microns on non-planar surfaces. The insulating part of the MEMS/PCB structure serves as a ramp ensuring continuity of the aerosol jet printed connection between the PCB and Si die. A 1 cm x 1 cm Si chip with custom MEMS microrobot was used to demonstrate the feasibility and flexibility of our approach in practice. After the fabrication, our interconnects were evaluated for conductivity and repeatability. The packaging and inspection process was carried out using our unique robotic system, Nexus, which integrates additive manufacturing, robotic transport, and metrology. Nexus allowed precision control during printing and transition between the main steps of manufacturing process: material deposition, curing, sintering, and microscope inspection. The results show that we successfully fabricated printed interconnects between copper PCB pads and Si die cleanroom fabricated gold pads, whereas electrical characterization revealed resistances in the range 1 Omega - 10 Omega. Our approach can be utilized in manufacturing of electrical interconnects for custom devices on different substrates including traditional and flexible PCBs. Furthermore, applied printing techniques enable the use of other insulating or conducting inks and formation of the structures of custom geometries at wide range of scale - 20 mu m to 1 mm.