Thermal Cyclic Fatigue Reliability of Printed Hybrid Electronics (PHE)

Additive manufacturing provides a pathway for manufacturing of printed hybrid electronic (PHE) assemblies in novel non-planar (curvilinear and 3D) form factors. In particular, PHEs may combine conventionally manufactured microelectronics components and circuit elements with additively manufactured features. Aerosol jet printing (AJP) is one of the leading additive manufacturing methods for PHEs. It is therefore critical to better understand the reliability aspects of using AJP-based PHEs to fully leverage the possibilities offered by this technology. This paper evaluates the reliability of nano-particle based metallic conductors in aerosol jet printed electronics (AJPE) under temperature cycling (TC) conditions for various substrates and supports the rapidly growing field of PHEs. PHE samples specifically designed and fabricated for this study consisting of substrates made of three different PCB materials (Glass-FR4, Kevlar-polyimide, Ceramic) were cycled to failure between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-40^{\circ} \mathrm{C}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$+125^{\circ} \mathrm{C}$</tex>. Finite element analysis (FEA) was used to quantify the different thermomechanical strain levels experienced by the conductor on the different substrate materials. The corresponding number of temperature cycles to failure were measured from the test and Weibull characteristic life was estimated for each substrate type. Failure analysis revealed that across all three substrates, the transition region connecting the printed traces to copper pads was where most of the failures occurred. The local geometric complexities at the transition region between the printed and conventional elements resulted in localized stressors. The FEA results confirm this strain concentration site. The failure experimental results, when combined with the local thermomechanical strain history at the failure site (estimated by the FEA), give useful insights into the design considerations needed for producing reliable AJPEs.