Aerosol Jet Printing for Three Dimensional Interconnects

Electrical connections between IC chips and printed circuit boards are typically accomplished by wire bonding. Although a mature technology, wire bonds have limitations due to increased package size, potential for damage during handling, and parasitic inductance which limits high frequency performance. With conformal interconnects, the electrical connections are printed with nanoparticle inks and then heated form solid conductive wires up the sidewall of die. Many advantages result including low profile, ultra thin connections, and high density packages. Unlike wire bonds, printed interconnects can be geometrically tailored to optimize impedance matching, with resulting frequency performance exceeding 90 GHz. Aerosol Jet® is a non-contact printing approach that when combined with multi-axis motion can print both metals and dielectrics in 3D multilayer geometries. The specific presentation will include results of high density gold interconnects, with 25 µm/25 µm line/space, between silicon bare die and alumina substrate. The first step is to print a dielectric fillet over the vertical die edge and junction with alumina. The fillet serves to insulate the die sidewall and form a mechanical buffer layer to match the thermal expansion of the Si, Alumina, and gold. Polyimide is preferred for its high working temperature (~250C) and capability to withstand thermal cycling to cryogenic temperatures. After curing the PI, nano-gold traces are printed between bond pads of the alumina and I/O on the die surface. The nano-gold can be sintered in an oven at 200C or laser sintered in situ to produce interconnect resistances below 1 Ohm.