Thermal–Mechanical Reliability of Strain Sensors Created Using Additive/Subtractive Hybrid Fabrication Process

In this study, six serpentine resistive strain sensors are manufactured on two cantilevers made of FR-4 (Flame Retardant 4) with dimensions of 25 mm × 140 mm. Three strain sensors are printed on each substrate using particle-free EI 615 silver ink. The method of fabrication is hybrid in nature and consists of aerosol jet (AJ) printing a layer of conductive material and selectively sintering certain regions before removing the non-sintered material with 1-dodecene solvent. The gauges on one cantilever are coated with a 10 µm dielectric layer using Norland Electronic Adhesives (NEA) 121, which serves as the passivation layer, while the three gauges on the other cantilever are left exposed. The samples are subjected to two standard thermal–mechanical loading conditions: namely, a vibration test according to the MIL-STD-883 method 2007 Cond A and a high-temperature soak test according to the Mil-Std-883 method 1008 Cond B. The reliability of the devices is quantified by assessing the percent change in their resistances and gauge factors (GF) between tests. The percent change is then used to ascribe a reliability metric to the gauges.