Die Attach and Thermal Cycling of Additively Manufactured Quad Flat No Lead Die Daisy Chain on Curved Alumina Substrate

Integration of electronic components into aerospace platforms offers the unique challenges of limited and constrained volumes. Utilizing non-planar surfaces allows for a drastic increase in the area available for electronics integration. Additive manufacturing (AM) can meet this need by working with a variety of substrate geometries to produce non-planar circuits capable of operating in harsh space environments. Here we demonstrate the use of aerosol jet printing (AJP) and dispense printing to integrate passive traces of a daisy chain to a silicon-based quad flat no lead (QFN) die onto curved 96% purity alumina substrates. Adhesion of multiple material interfaces was tested to determine the compatibility of different components. AJP was used to fabricate all traces and bond pads using silver-based ink. Assembly was completed by depositing a conductive epoxy to attach the die. Samples were placed in an environmental chamber and cycled between –55°C and 125°C for 10 cycles as per MIL-STD-883, M1010, Condition B. Afterwards, the change in resistance was measured for all lines in the fabricated daisy chain. All interfaces provided strong adhesion since the failure mode of most interfaces was adhesive failure and not cohesive failure between the deposited layers and substrate. The only interface which experienced consistent cohesive failure was the conductor on the dielectric pad. Despite the failure mode, this material was selected as the adhesive force was still acceptable. Two samples fabricated on convex and concave alumina substrates were subjected to thermal cycling to study the effect of temperature variation on the assembly, and the results found that no variance in the lines resistance exceeded a ±10% change in resistance. Overall, the devices performed well with changes in resistance being better mitigated by thicker conductive layers. The additive manufacturing techniques demonstrated in this work enhance the electronic industry by improving performance and reliability while simultaneously reducing the material cost and waste.