By Chris Riso
The advent of 5G has brought on requirements for higher operating frequencies, thus creating a demand for radio-frequency (RF) components which must meet high performance standards, while complying with the miniaturization trend of current-day circuit design. RF components (such as inductors) often require complex non-planar geometries such as conical-helices and toroids. As a result, additive manufacturing (AM) techniques offer ideal approaches for fabricating such miniaturized 3D components that can also satisfy performance goals.
Due to the intricacy and novelty of the interactions between ink materials, 3D geometries and print processes used, AM RF electronics face tremendous challenges, specifically in regard to reliability and durability. AM can also be used as an on-site repair method, to increase availability and extend the life-cycle of complex RF electronics during extend missions in remote locations. In this presentation, the repairability of simple RF circuitry is first demonstrated. The baseline test coupons are microstrips and coplanar waveguides where ‘damage’ is intentionally introduced into error-seeded specimens and then repair methods are developed through AM techniques. The repaired coupons undergo thermal cycling for reliability assessment concurrent with ‘pristine’ (undamaged) baseline samples, to validate the performance of the repaired samples. Next, the repair of a complex 3D micro solenoid inductor, fabricated on a 5-axis Aerosol Jet printer, is presented. This complex 3D device has multiple vulnerable areas that are prone to failure due to stress concentrations caused by the component architecture.
In fact, one of the fabricated test specimens was found to have failed shortly after fabrication. AM repairs were able to restore the complex structure to the original RF performance, both in the interconnects as well as on the curvilinear core. Reliability of these AM repairs are investigated by exploring the effect of accelerated thermal cycling tests on the RF performance. RF performance of these test specimens are modeled before and after AM repairs, using multi-physics finite element analysis (FEA) of the electromagnetic performance and the thermo-mechanical stress fields. The end goal is to quantify the effect of thermal cycling damage accumulation and to combine the test results with modeling insights to formulate acceleration factors that can estimate the expected life-cycle reliability.